Imaging

SCOTTSDALE, ARIZ. — Duplex ultrasound with contrast enhancement delivered by continuous infusion shows promise in the detection of endoleaks following endovascular aneurysm repair, Dr. Ruth L. Bush said at an international congress on endovascular interventions sponsored by the Arizona Heart Institute.

“Our early results strongly suggest that contrast enhancement with a continuous infusion technique could be used as a primary diagnostic imaging modality for follow-up endograft surveillance,” possibly replacing CT as the standard for graft surveillance, said Dr. Bush of the Baylor College of Medicine, Houston.

Following endovascular aneurysm repair (EVAR), patients must be assessed periodically for sac size, stent-graft integrity, and endoleaks. CT is a fine imaging modality for this surveillance, but at the cost of substantial doses of ionizing radiation and exposure to iodinated contrast media, which can be nephrotoxic. Furthermore, CT scanning is expensive. According to some reports, more than 65% of postoperative costs following EVAR are related to CT scanning.

Unfortunately, color duplex ultrasound has been shown to have a lower sensitivity and a lower positive predictive value than CT has in this surveillance. Delivery of contrast enhancement in a bolus improves echogenicity and can even detect slow endoleaks that are not visible in CT. But the disadvantage of this technique is that bolus injection of the contrast medium allows for only a short scanning time—less than 10 minutes—so multiple injections are usually necessary. The contrast is provided by microbubbles, which must be small enough to pass through the pulmonary capillaries. The various gas microbubble contrast media are generally considered safe and to have low toxicity. However, it has proven difficult to maintain these microbubbles in the systemic circulation.

Some of these problems are avoided by continuous infusion of the contrast medium. Dr. Bush uses a syringe filled with contrast medium and normal saline and infuses the mixture at the rate of 4 cc/min to extend the scanning time to 20 minutes or more.

In a preliminary study in 20 patients, contrast-enhanced ultrasound found one type 1 endoleak and nine type 2 endoleaks. In those same patients, color duplex ultrasound found one type 1 endoleak and only four type 2 endoleaks, and CT found one type 1 endoleak and six type 2 endoleaks.

The patients' body type affected scanning time. The investigators noted a direct relationship between scanning time and body mass index.

And it's important to control scanning parameters carefully. For one thing, the syringe holding the contrast medium needs to be agitated continually to avoid breakdown of the microbubbles.

And it's necessary to optimize the harmonic imaging on the ultrasound machines, decrease the mechanical index and the compression, and adjust the focal zone to be below the aorta.

“All of this was done in an attempt to maintain the integrity of the microbubbles,” Dr. Bush said. “If you have a mechanical index turned up too high or the compression and the focal zone adjusted [imperfectly], the microbubbles would shatter and you won't get a good result.”

The learning curve for this technique is about 10–15 patients, she said.

Delivery of contrast enhancement in a bolus can even detect slow endoleaks that are not visible in CT. DR. BUSH

SCOTTSDALE, ARIZ. — Duplex ultrasound with contrast enhancement delivered by continuous infusion shows promise in the detection of endoleaks following endovascular aneurysm repair, Dr. Ruth L. Bush said at an international congress on endovascular interventions sponsored by the Arizona Heart Institute.

“Our early results strongly suggest that contrast enhancement with a continuous infusion technique could be used as a primary diagnostic imaging modality for follow-up endograft surveillance,” possibly replacing CT as the standard for graft surveillance, said Dr. Bush of the Baylor College of Medicine, Houston.

Following endovascular aneurysm repair (EVAR), patients must be assessed periodically for sac size, stent-graft integrity, and endoleaks. CT is a fine imaging modality for this surveillance, but at the cost of substantial doses of ionizing radiation and exposure to iodinated contrast media, which can be nephrotoxic. Furthermore, CT scanning is expensive. According to some reports, more than 65% of postoperative costs following EVAR are related to CT scanning.

Unfortunately, color duplex ultrasound has been shown to have a lower sensitivity and a lower positive predictive value than CT has in this surveillance. Delivery of contrast enhancement in a bolus improves echogenicity and can even detect slow endoleaks that are not visible in CT. But the disadvantage of this technique is that bolus injection of the contrast medium allows for only a short scanning time—less than 10 minutes—so multiple injections are usually necessary. The contrast is provided by microbubbles, which must be small enough to pass through the pulmonary capillaries. The various gas microbubble contrast media are generally considered safe and to have low toxicity. However, it has proven difficult to maintain these microbubbles in the systemic circulation.

Some of these problems are avoided by continuous infusion of the contrast medium. Dr. Bush uses a syringe filled with contrast medium and normal saline and infuses the mixture at the rate of 4 cc/min to extend the scanning time to 20 minutes or more.

In a preliminary study in 20 patients, contrast-enhanced ultrasound found one type 1 endoleak and nine type 2 endoleaks. In those same patients, color duplex ultrasound found one type 1 endoleak and only four type 2 endoleaks, and CT found one type 1 endoleak and six type 2 endoleaks.

The patients' body type affected scanning time. The investigators noted a direct relationship between scanning time and body mass index.

And it's important to control scanning parameters carefully. For one thing, the syringe holding the contrast medium needs to be agitated continually to avoid breakdown of the microbubbles.

And it's necessary to optimize the harmonic imaging on the ultrasound machines, decrease the mechanical index and the compression, and adjust the focal zone to be below the aorta.

“All of this was done in an attempt to maintain the integrity of the microbubbles,” Dr. Bush said. “If you have a mechanical index turned up too high or the compression and the focal zone adjusted [imperfectly], the microbubbles would shatter and you won't get a good result.”

The learning curve for this technique is about 10–15 patients, she said.

Delivery of contrast enhancement in a bolus can even detect slow endoleaks that are not visible in CT. DR. BUSH

SCOTTSDALE, ARIZ. — Duplex ultrasound with contrast enhancement delivered by continuous infusion shows promise in the detection of endoleaks following endovascular aneurysm repair, Dr. Ruth L. Bush said at an international congress on endovascular interventions sponsored by the Arizona Heart Institute.

“Our early results strongly suggest that contrast enhancement with a continuous infusion technique could be used as a primary diagnostic imaging modality for follow-up endograft surveillance,” possibly replacing CT as the standard for graft surveillance, said Dr. Bush of the Baylor College of Medicine, Houston.

Following endovascular aneurysm repair (EVAR), patients must be assessed periodically for sac size, stent-graft integrity, and endoleaks. CT is a fine imaging modality for this surveillance, but at the cost of substantial doses of ionizing radiation and exposure to iodinated contrast media, which can be nephrotoxic. Furthermore, CT scanning is expensive. According to some reports, more than 65% of postoperative costs following EVAR are related to CT scanning.

Unfortunately, color duplex ultrasound has been shown to have a lower sensitivity and a lower positive predictive value than CT has in this surveillance. Delivery of contrast enhancement in a bolus improves echogenicity and can even detect slow endoleaks that are not visible in CT. But the disadvantage of this technique is that bolus injection of the contrast medium allows for only a short scanning time—less than 10 minutes—so multiple injections are usually necessary. The contrast is provided by microbubbles, which must be small enough to pass through the pulmonary capillaries. The various gas microbubble contrast media are generally considered safe and to have low toxicity. However, it has proven difficult to maintain these microbubbles in the systemic circulation.

Some of these problems are avoided by continuous infusion of the contrast medium. Dr. Bush uses a syringe filled with contrast medium and normal saline and infuses the mixture at the rate of 4 cc/min to extend the scanning time to 20 minutes or more.

In a preliminary study in 20 patients, contrast-enhanced ultrasound found one type 1 endoleak and nine type 2 endoleaks. In those same patients, color duplex ultrasound found one type 1 endoleak and only four type 2 endoleaks, and CT found one type 1 endoleak and six type 2 endoleaks.

The patients' body type affected scanning time. The investigators noted a direct relationship between scanning time and body mass index.

And it's important to control scanning parameters carefully. For one thing, the syringe holding the contrast medium needs to be agitated continually to avoid breakdown of the microbubbles.

And it's necessary to optimize the harmonic imaging on the ultrasound machines, decrease the mechanical index and the compression, and adjust the focal zone to be below the aorta.

“All of this was done in an attempt to maintain the integrity of the microbubbles,” Dr. Bush said. “If you have a mechanical index turned up too high or the compression and the focal zone adjusted [imperfectly], the microbubbles would shatter and you won't get a good result.”

The learning curve for this technique is about 10–15 patients, she said.

Delivery of contrast enhancement in a bolus can even detect slow endoleaks that are not visible in CT. DR. BUSH

ORLANDO — Echocardiography overestimates the true prevalence of primary pulmonary hypertension in hemodialysis patients with end-stage renal disease, according to a study presented at a meeting sponsored by the National Kidney Foundation.

For this reason, hemodialysis patients with echocardiographic evidence of pulmonary artery hypertension (PAH) should undergo right heart catheterization for confirmation, Dr. Ifeanyi Isaiah and colleagues, of Temple University, Philadelphia, wrote in a poster.

The reported prevalence of PAH in hemodialysis patients ranges from 27% to 40%, but these numbers are based on studies that relied exclusively on echocardiographic estimates of pulmonary arterial pressures to make the diagnosis.

The more accurate way of making the diagnosis is with right heart catheterization, Dr. Isaiah and colleagues wrote.

To establish the true prevalence of PAH in this population, the investigators conducted a retrospective, observational analysis of all echocardiographic and right heart catheterization studies done in their outpatient hemodialysis unit from January 2000 to December 2006.

Of the 502 patients included in the analysis, the majority (439 patients, or 87.5%) had undergone echocardiography. Pulmonary arterial pressure greater than 40 mm Hg, suggesting the presence ofPAH, was documented in 127 of the echocardiography patients (28.9%).

Data for right heart catheterization, which were available for 22 of these 127 patients, showed that 11 (50%) of them had elevated pulmonary arterial pressure.

Although the results showed that pulmonary hypertension may be overestimated, the study also “confirms a higher prevalence of pulmonary hypertension in end-stage renal disease patients receiving hemodialysis than [in] the general population,” the investigators wrote.

In addition to providing a more accurate diagnosis of PAH in hemodialysis patients, right heart catheterization is valuable in distinguishing those patients whose elevated pulmonary pressure results from heart failure from those who have isolated PAH with no heart failure, they added.

ORLANDO — Echocardiography overestimates the true prevalence of primary pulmonary hypertension in hemodialysis patients with end-stage renal disease, according to a study presented at a meeting sponsored by the National Kidney Foundation.

For this reason, hemodialysis patients with echocardiographic evidence of pulmonary artery hypertension (PAH) should undergo right heart catheterization for confirmation, Dr. Ifeanyi Isaiah and colleagues, of Temple University, Philadelphia, wrote in a poster.

The reported prevalence of PAH in hemodialysis patients ranges from 27% to 40%, but these numbers are based on studies that relied exclusively on echocardiographic estimates of pulmonary arterial pressures to make the diagnosis.

The more accurate way of making the diagnosis is with right heart catheterization, Dr. Isaiah and colleagues wrote.

To establish the true prevalence of PAH in this population, the investigators conducted a retrospective, observational analysis of all echocardiographic and right heart catheterization studies done in their outpatient hemodialysis unit from January 2000 to December 2006.

Of the 502 patients included in the analysis, the majority (439 patients, or 87.5%) had undergone echocardiography. Pulmonary arterial pressure greater than 40 mm Hg, suggesting the presence ofPAH, was documented in 127 of the echocardiography patients (28.9%).

Data for right heart catheterization, which were available for 22 of these 127 patients, showed that 11 (50%) of them had elevated pulmonary arterial pressure.

Although the results showed that pulmonary hypertension may be overestimated, the study also “confirms a higher prevalence of pulmonary hypertension in end-stage renal disease patients receiving hemodialysis than [in] the general population,” the investigators wrote.

In addition to providing a more accurate diagnosis of PAH in hemodialysis patients, right heart catheterization is valuable in distinguishing those patients whose elevated pulmonary pressure results from heart failure from those who have isolated PAH with no heart failure, they added.

ORLANDO — Echocardiography overestimates the true prevalence of primary pulmonary hypertension in hemodialysis patients with end-stage renal disease, according to a study presented at a meeting sponsored by the National Kidney Foundation.

For this reason, hemodialysis patients with echocardiographic evidence of pulmonary artery hypertension (PAH) should undergo right heart catheterization for confirmation, Dr. Ifeanyi Isaiah and colleagues, of Temple University, Philadelphia, wrote in a poster.

The reported prevalence of PAH in hemodialysis patients ranges from 27% to 40%, but these numbers are based on studies that relied exclusively on echocardiographic estimates of pulmonary arterial pressures to make the diagnosis.

The more accurate way of making the diagnosis is with right heart catheterization, Dr. Isaiah and colleagues wrote.

To establish the true prevalence of PAH in this population, the investigators conducted a retrospective, observational analysis of all echocardiographic and right heart catheterization studies done in their outpatient hemodialysis unit from January 2000 to December 2006.

Of the 502 patients included in the analysis, the majority (439 patients, or 87.5%) had undergone echocardiography. Pulmonary arterial pressure greater than 40 mm Hg, suggesting the presence ofPAH, was documented in 127 of the echocardiography patients (28.9%).

Data for right heart catheterization, which were available for 22 of these 127 patients, showed that 11 (50%) of them had elevated pulmonary arterial pressure.

Although the results showed that pulmonary hypertension may be overestimated, the study also “confirms a higher prevalence of pulmonary hypertension in end-stage renal disease patients receiving hemodialysis than [in] the general population,” the investigators wrote.

In addition to providing a more accurate diagnosis of PAH in hemodialysis patients, right heart catheterization is valuable in distinguishing those patients whose elevated pulmonary pressure results from heart failure from those who have isolated PAH with no heart failure, they added.

NEW ORLEANS — Periprocedural intravenous hydration with sodium bicarbonate is no more effective than normal saline for prevention of contrast-induced nephropathy in patients undergoing coronary angiography, Dr. Somjot S. Brar reported at a conference sponsored by the American College of Cardiology.

He presented a single-center randomized trial in 353 patients undergoing coronary angiography, all with at least moderate kidney dysfunction, defined as a baseline glomerular filtration rate (GFR) of 60 mL/min per 1.73 m

The primary end point—contrast-induced nephropathy (CIN) as defined by a 25% or greater decline in GFR within 4 days—occurred in 13.6% of the sodium bicarbonate group and 13.5% on normal saline, the most commonly used hydration fluid in clinical practice, said Dr. Brar of Kaiser Permanente Medical Center, Los Angeles.

The secondary end point—at least a 25% increase in creatinine—occurred in 16.3% on sodium bicarbonate and 15.4% on 0.9% sodium chloride. No patient subgroup fared significantly better on sodium bicarbonatein in the trial, sponsored by Kaiser Permanente. Half of patients in each study arm received Mucomyst (acetylcysteine); their outcomes were similar to those who didn't.

The incidence of CIN ranged from less than 1% in patients with only one CIN risk factor to 37% in those with six or more. The known CIN risk factors are a low GFR, age greater than 75, diabetes, hypertension, a history of heart failure, anemia, inpatient status, a contrast volume in excess of 150 mL, and female gender, he added.

Fully 47% of patients who developed CIN had persistent kidney dysfunction, compared with baseline at 2–8 weeks post procedure. Thirty-day all-cause mortality was 2.0% in the sodium bicarbonate group and 1.3% with sodium chloride. One patient in the saline arm went on dialysis within 30 days.

“One of the fundamental problems we have in treating CIN is while we can identify patients at risk for it we obviously don't have any effective way to reduce their risk. Having rates of CIN of up to 37% is clearly unacceptable and something needs to be done for these patients,” Dr. Brar said at the conference, also sponsored by the Society for Cardiovascular Angiography and Interventions.

Ultrafiltration has been proposed as a possible solution. However, it's quite expensive and not widely available. “Perhaps the answer will be intraarterial administration of a pharmacologic agent, where infusion directly into the kidneys might be more effective. I think there are still some possibilities to test,” he said.

For now, the best evidence for prevention of CIN remains “hydration, hydration, hydration—and the best fluid we have evidence for is normal saline,” according to Dr. Brar.

The theory behind using sodium bicarbonate was it would address both mechanisms involved in CIN. The sodium would attenuate contrast-induced renal vasoconstriction, while the bicarbonate would reduce oxidative stress by raising tubular pH.

One prior randomized trial in which sodium bicarbonate outperformed normal saline in preventing CIN. But that study included patients undergoing a variety of procedures, while the Kaiser study involved a single uniform intervention.

It's also possible that other investigators didn't follow patients long enough to pick up all cases of CIN.

“We had 10 patients in the sodium bicarbonate group who didn't meet criteria for CIN on day 1 or 2 but did on day 3 or 4. This raises the possibility in my mind that with sodium bicarbonate we may delay onset of CIN as opposed to preventing it,” he said.

'Having rates of CIN of up to 37% is clearly unacceptable and something needs to be done for these patients.' DR. BRAR

NEW ORLEANS — Periprocedural intravenous hydration with sodium bicarbonate is no more effective than normal saline for prevention of contrast-induced nephropathy in patients undergoing coronary angiography, Dr. Somjot S. Brar reported at a conference sponsored by the American College of Cardiology.

He presented a single-center randomized trial in 353 patients undergoing coronary angiography, all with at least moderate kidney dysfunction, defined as a baseline glomerular filtration rate (GFR) of 60 mL/min per 1.73 m

The primary end point—contrast-induced nephropathy (CIN) as defined by a 25% or greater decline in GFR within 4 days—occurred in 13.6% of the sodium bicarbonate group and 13.5% on normal saline, the most commonly used hydration fluid in clinical practice, said Dr. Brar of Kaiser Permanente Medical Center, Los Angeles.

The secondary end point—at least a 25% increase in creatinine—occurred in 16.3% on sodium bicarbonate and 15.4% on 0.9% sodium chloride. No patient subgroup fared significantly better on sodium bicarbonatein in the trial, sponsored by Kaiser Permanente. Half of patients in each study arm received Mucomyst (acetylcysteine); their outcomes were similar to those who didn't.

The incidence of CIN ranged from less than 1% in patients with only one CIN risk factor to 37% in those with six or more. The known CIN risk factors are a low GFR, age greater than 75, diabetes, hypertension, a history of heart failure, anemia, inpatient status, a contrast volume in excess of 150 mL, and female gender, he added.

Fully 47% of patients who developed CIN had persistent kidney dysfunction, compared with baseline at 2–8 weeks post procedure. Thirty-day all-cause mortality was 2.0% in the sodium bicarbonate group and 1.3% with sodium chloride. One patient in the saline arm went on dialysis within 30 days.

“One of the fundamental problems we have in treating CIN is while we can identify patients at risk for it we obviously don't have any effective way to reduce their risk. Having rates of CIN of up to 37% is clearly unacceptable and something needs to be done for these patients,” Dr. Brar said at the conference, also sponsored by the Society for Cardiovascular Angiography and Interventions.

Ultrafiltration has been proposed as a possible solution. However, it's quite expensive and not widely available. “Perhaps the answer will be intraarterial administration of a pharmacologic agent, where infusion directly into the kidneys might be more effective. I think there are still some possibilities to test,” he said.

For now, the best evidence for prevention of CIN remains “hydration, hydration, hydration—and the best fluid we have evidence for is normal saline,” according to Dr. Brar.

The theory behind using sodium bicarbonate was it would address both mechanisms involved in CIN. The sodium would attenuate contrast-induced renal vasoconstriction, while the bicarbonate would reduce oxidative stress by raising tubular pH.

One prior randomized trial in which sodium bicarbonate outperformed normal saline in preventing CIN. But that study included patients undergoing a variety of procedures, while the Kaiser study involved a single uniform intervention.

It's also possible that other investigators didn't follow patients long enough to pick up all cases of CIN.

“We had 10 patients in the sodium bicarbonate group who didn't meet criteria for CIN on day 1 or 2 but did on day 3 or 4. This raises the possibility in my mind that with sodium bicarbonate we may delay onset of CIN as opposed to preventing it,” he said.

'Having rates of CIN of up to 37% is clearly unacceptable and something needs to be done for these patients.' DR. BRAR

NEW ORLEANS — Periprocedural intravenous hydration with sodium bicarbonate is no more effective than normal saline for prevention of contrast-induced nephropathy in patients undergoing coronary angiography, Dr. Somjot S. Brar reported at a conference sponsored by the American College of Cardiology.

He presented a single-center randomized trial in 353 patients undergoing coronary angiography, all with at least moderate kidney dysfunction, defined as a baseline glomerular filtration rate (GFR) of 60 mL/min per 1.73 m

The primary end point—contrast-induced nephropathy (CIN) as defined by a 25% or greater decline in GFR within 4 days—occurred in 13.6% of the sodium bicarbonate group and 13.5% on normal saline, the most commonly used hydration fluid in clinical practice, said Dr. Brar of Kaiser Permanente Medical Center, Los Angeles.

The secondary end point—at least a 25% increase in creatinine—occurred in 16.3% on sodium bicarbonate and 15.4% on 0.9% sodium chloride. No patient subgroup fared significantly better on sodium bicarbonatein in the trial, sponsored by Kaiser Permanente. Half of patients in each study arm received Mucomyst (acetylcysteine); their outcomes were similar to those who didn't.

The incidence of CIN ranged from less than 1% in patients with only one CIN risk factor to 37% in those with six or more. The known CIN risk factors are a low GFR, age greater than 75, diabetes, hypertension, a history of heart failure, anemia, inpatient status, a contrast volume in excess of 150 mL, and female gender, he added.

Fully 47% of patients who developed CIN had persistent kidney dysfunction, compared with baseline at 2–8 weeks post procedure. Thirty-day all-cause mortality was 2.0% in the sodium bicarbonate group and 1.3% with sodium chloride. One patient in the saline arm went on dialysis within 30 days.

“One of the fundamental problems we have in treating CIN is while we can identify patients at risk for it we obviously don't have any effective way to reduce their risk. Having rates of CIN of up to 37% is clearly unacceptable and something needs to be done for these patients,” Dr. Brar said at the conference, also sponsored by the Society for Cardiovascular Angiography and Interventions.

Ultrafiltration has been proposed as a possible solution. However, it's quite expensive and not widely available. “Perhaps the answer will be intraarterial administration of a pharmacologic agent, where infusion directly into the kidneys might be more effective. I think there are still some possibilities to test,” he said.

For now, the best evidence for prevention of CIN remains “hydration, hydration, hydration—and the best fluid we have evidence for is normal saline,” according to Dr. Brar.

The theory behind using sodium bicarbonate was it would address both mechanisms involved in CIN. The sodium would attenuate contrast-induced renal vasoconstriction, while the bicarbonate would reduce oxidative stress by raising tubular pH.

One prior randomized trial in which sodium bicarbonate outperformed normal saline in preventing CIN. But that study included patients undergoing a variety of procedures, while the Kaiser study involved a single uniform intervention.

It's also possible that other investigators didn't follow patients long enough to pick up all cases of CIN.

“We had 10 patients in the sodium bicarbonate group who didn't meet criteria for CIN on day 1 or 2 but did on day 3 or 4. This raises the possibility in my mind that with sodium bicarbonate we may delay onset of CIN as opposed to preventing it,” he said.

'Having rates of CIN of up to 37% is clearly unacceptable and something needs to be done for these patients.' DR. BRAR

TAMPA — Dual-energy x-ray absorptiometry is an excellent method to measure and monitor body composition changes in obese patients undergoing weight loss and to assess body composition in athletes, Dr. Mary K. Oates reported at the annual meeting of the International Society for Clinical Densitometry.

Although this application is not reimbursable by medical insurance, many patients concerned about fitness and weight loss are willing to pay out of pocket to have a direct measurement of their percent lean mass and percent fat, said Dr. Oates, who is board certified in physical medicine and rehabilitation and has private clinics in Santa Maria and Pismo Beach, Calif.

Unlike other methods for assessing body composition, dual-energy x-ray absorptiometry (DXA) “can give you regional values, not just total body fat,” she said. “Olympic athletes and professional athletes want to know, How much muscle do I have in my leg? How much muscle did my injured quarterback lose in his throwing arm after his injury?” DXA also provides a dramatic total body image of the skeleton and soft tissue.

DXA is being used by the Green Bay Packers pro football team and at the U.S. Olympic Training Center in Colorado Springs to provide benchmarks for performance enhancement, she said.

Most methods that have been widely used to estimate body composition are indirect. Epidemiology studies usually rely on measurement of waist and hip circumferences and calculation of waist:hip ratio, as well as body mass index. Determination of BMI is often used to define obesity, although BMI does not account for percent body fat. A nonobese, muscular individual may have a BMI score in the obese range.

Digital scales use bioelectrical impedance analysis to estimate percent body fat. Another indirect method that is widely used in health clubs is skin-fold measurement, in which calipers measure the skin at the back of the upper arms or the stomach ("pinch test").

Calculation of total body fat is based on the assumption that the amount of subcutaneous fat is proportional to the total body fat.

“It is assumed that about one-third of the total fat is located subcutaneously, but we all know that it varies with sex, age, ethnicity, and individual fat distribution,” Dr. Oates said.

The “dunk tank” has traditionally been considered the most accurate way to determine body composition, although it is technically difficult for the subject to perform. The Bod Pod is similar to the “dunk tank” but is based on air displacement, rather than water displacement.

In contrast, DXA directly measures fat mass, lean mass, and bone mineral content, and calculates the percentages of fat mass and lean mass. One limitation of DXA is the inability to measure the fat or lean composition of pixels that contain bone, although composition can be estimated from the adjacent pixels.

Different DXA machines have various limits on patient thickness and weight, and most models can't accommodate obese patients who weigh 300 pounds or more, so it's necessary to do a right-sided scan, then double the results to get whole-body estimates, Dr. Oates said. The new Lunar iDXA by GE has a larger table size and weight capacity that allows direct full-body measurement of patients up to 450 pounds and up to 6 feet 5 inches in height.

Individuals who have undergone body fat assessment by another method may be reluctant to accept the DXA results: The percentage of fat may generally be a little higher with DXA than with other methods. “I think that's because we are really measuring three compartments—we are measuring fat, we are measuring muscle, we are measuring bone,” said Dr. Oates, a medical consultant to GE Healthcare Lunar. “The other methods are just estimating from body density.”

To demonstrate the usefulness of DXA in monitoring body composition changes, Dr. Oates offered to work with the producers of “The Biggest Loser,” an NBC television reality show in which morbidly obese contestants compete to lose weight through aggressive diet and exercise. DXA provided a graphic visual image of the weight loss and changes in percent body fat of the contestants.

DXA scans can be a powerful motivational tool for patients in weight-loss programs. One advantage of DXA in monitoring weight loss is illustrated by the case of a contestant whose apparent fat loss was greater than the 30-pound weight loss indicated by the scales.

DXA results showed that he had gained 16.5 pounds of muscle. “Muscle weighs more than fat,” Dr. Oates said. “We now can see the breakdown of total weight loss.” The contestant eventually went from 39% body fat to 5.8% body fat.

DXA scans show a 105-kg woman with 53% total body fat before aggressive diet and exercise program (left) and after the program at 57 kg, with 18% total body fat (right). Photos courtesy Dr. Robert Huizenga/Dr. Mary K. Oates

TAMPA — Dual-energy x-ray absorptiometry is an excellent method to measure and monitor body composition changes in obese patients undergoing weight loss and to assess body composition in athletes, Dr. Mary K. Oates reported at the annual meeting of the International Society for Clinical Densitometry.

Although this application is not reimbursable by medical insurance, many patients concerned about fitness and weight loss are willing to pay out of pocket to have a direct measurement of their percent lean mass and percent fat, said Dr. Oates, who is board certified in physical medicine and rehabilitation and has private clinics in Santa Maria and Pismo Beach, Calif.

Unlike other methods for assessing body composition, dual-energy x-ray absorptiometry (DXA) “can give you regional values, not just total body fat,” she said. “Olympic athletes and professional athletes want to know, How much muscle do I have in my leg? How much muscle did my injured quarterback lose in his throwing arm after his injury?” DXA also provides a dramatic total body image of the skeleton and soft tissue.

DXA is being used by the Green Bay Packers pro football team and at the U.S. Olympic Training Center in Colorado Springs to provide benchmarks for performance enhancement, she said.

Most methods that have been widely used to estimate body composition are indirect. Epidemiology studies usually rely on measurement of waist and hip circumferences and calculation of waist:hip ratio, as well as body mass index. Determination of BMI is often used to define obesity, although BMI does not account for percent body fat. A nonobese, muscular individual may have a BMI score in the obese range.

Digital scales use bioelectrical impedance analysis to estimate percent body fat. Another indirect method that is widely used in health clubs is skin-fold measurement, in which calipers measure the skin at the back of the upper arms or the stomach ("pinch test").

Calculation of total body fat is based on the assumption that the amount of subcutaneous fat is proportional to the total body fat.

“It is assumed that about one-third of the total fat is located subcutaneously, but we all know that it varies with sex, age, ethnicity, and individual fat distribution,” Dr. Oates said.

The “dunk tank” has traditionally been considered the most accurate way to determine body composition, although it is technically difficult for the subject to perform. The Bod Pod is similar to the “dunk tank” but is based on air displacement, rather than water displacement.

In contrast, DXA directly measures fat mass, lean mass, and bone mineral content, and calculates the percentages of fat mass and lean mass. One limitation of DXA is the inability to measure the fat or lean composition of pixels that contain bone, although composition can be estimated from the adjacent pixels.

Different DXA machines have various limits on patient thickness and weight, and most models can't accommodate obese patients who weigh 300 pounds or more, so it's necessary to do a right-sided scan, then double the results to get whole-body estimates, Dr. Oates said. The new Lunar iDXA by GE has a larger table size and weight capacity that allows direct full-body measurement of patients up to 450 pounds and up to 6 feet 5 inches in height.

Individuals who have undergone body fat assessment by another method may be reluctant to accept the DXA results: The percentage of fat may generally be a little higher with DXA than with other methods. “I think that's because we are really measuring three compartments—we are measuring fat, we are measuring muscle, we are measuring bone,” said Dr. Oates, a medical consultant to GE Healthcare Lunar. “The other methods are just estimating from body density.”

To demonstrate the usefulness of DXA in monitoring body composition changes, Dr. Oates offered to work with the producers of “The Biggest Loser,” an NBC television reality show in which morbidly obese contestants compete to lose weight through aggressive diet and exercise. DXA provided a graphic visual image of the weight loss and changes in percent body fat of the contestants.

DXA scans can be a powerful motivational tool for patients in weight-loss programs. One advantage of DXA in monitoring weight loss is illustrated by the case of a contestant whose apparent fat loss was greater than the 30-pound weight loss indicated by the scales.

DXA results showed that he had gained 16.5 pounds of muscle. “Muscle weighs more than fat,” Dr. Oates said. “We now can see the breakdown of total weight loss.” The contestant eventually went from 39% body fat to 5.8% body fat.

DXA scans show a 105-kg woman with 53% total body fat before aggressive diet and exercise program (left) and after the program at 57 kg, with 18% total body fat (right). Photos courtesy Dr. Robert Huizenga/Dr. Mary K. Oates

TAMPA — Dual-energy x-ray absorptiometry is an excellent method to measure and monitor body composition changes in obese patients undergoing weight loss and to assess body composition in athletes, Dr. Mary K. Oates reported at the annual meeting of the International Society for Clinical Densitometry.

Although this application is not reimbursable by medical insurance, many patients concerned about fitness and weight loss are willing to pay out of pocket to have a direct measurement of their percent lean mass and percent fat, said Dr. Oates, who is board certified in physical medicine and rehabilitation and has private clinics in Santa Maria and Pismo Beach, Calif.

Unlike other methods for assessing body composition, dual-energy x-ray absorptiometry (DXA) “can give you regional values, not just total body fat,” she said. “Olympic athletes and professional athletes want to know, How much muscle do I have in my leg? How much muscle did my injured quarterback lose in his throwing arm after his injury?” DXA also provides a dramatic total body image of the skeleton and soft tissue.

DXA is being used by the Green Bay Packers pro football team and at the U.S. Olympic Training Center in Colorado Springs to provide benchmarks for performance enhancement, she said.

Most methods that have been widely used to estimate body composition are indirect. Epidemiology studies usually rely on measurement of waist and hip circumferences and calculation of waist:hip ratio, as well as body mass index. Determination of BMI is often used to define obesity, although BMI does not account for percent body fat. A nonobese, muscular individual may have a BMI score in the obese range.

Digital scales use bioelectrical impedance analysis to estimate percent body fat. Another indirect method that is widely used in health clubs is skin-fold measurement, in which calipers measure the skin at the back of the upper arms or the stomach ("pinch test").

Calculation of total body fat is based on the assumption that the amount of subcutaneous fat is proportional to the total body fat.

“It is assumed that about one-third of the total fat is located subcutaneously, but we all know that it varies with sex, age, ethnicity, and individual fat distribution,” Dr. Oates said.

The “dunk tank” has traditionally been considered the most accurate way to determine body composition, although it is technically difficult for the subject to perform. The Bod Pod is similar to the “dunk tank” but is based on air displacement, rather than water displacement.

In contrast, DXA directly measures fat mass, lean mass, and bone mineral content, and calculates the percentages of fat mass and lean mass. One limitation of DXA is the inability to measure the fat or lean composition of pixels that contain bone, although composition can be estimated from the adjacent pixels.

Different DXA machines have various limits on patient thickness and weight, and most models can't accommodate obese patients who weigh 300 pounds or more, so it's necessary to do a right-sided scan, then double the results to get whole-body estimates, Dr. Oates said. The new Lunar iDXA by GE has a larger table size and weight capacity that allows direct full-body measurement of patients up to 450 pounds and up to 6 feet 5 inches in height.

Individuals who have undergone body fat assessment by another method may be reluctant to accept the DXA results: The percentage of fat may generally be a little higher with DXA than with other methods. “I think that's because we are really measuring three compartments—we are measuring fat, we are measuring muscle, we are measuring bone,” said Dr. Oates, a medical consultant to GE Healthcare Lunar. “The other methods are just estimating from body density.”

To demonstrate the usefulness of DXA in monitoring body composition changes, Dr. Oates offered to work with the producers of “The Biggest Loser,” an NBC television reality show in which morbidly obese contestants compete to lose weight through aggressive diet and exercise. DXA provided a graphic visual image of the weight loss and changes in percent body fat of the contestants.

DXA scans can be a powerful motivational tool for patients in weight-loss programs. One advantage of DXA in monitoring weight loss is illustrated by the case of a contestant whose apparent fat loss was greater than the 30-pound weight loss indicated by the scales.

DXA results showed that he had gained 16.5 pounds of muscle. “Muscle weighs more than fat,” Dr. Oates said. “We now can see the breakdown of total weight loss.” The contestant eventually went from 39% body fat to 5.8% body fat.

DXA scans show a 105-kg woman with 53% total body fat before aggressive diet and exercise program (left) and after the program at 57 kg, with 18% total body fat (right). Photos courtesy Dr. Robert Huizenga/Dr. Mary K. Oates

SAN DIEGO — An old medical myth—that patients who are allergic to seafood are at risk of adverse reactions to radiologic contrast media—persists even among cardiologists, despite having been thoroughly debunked, Dr. Andrew D. Beaty reported at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.

In a survey of 231 specialists at six academic medical centers, 69% of the physicians admitted asking patients about seafood allergy before radiologic procedures using contrast media. Of those surveyed, 37% of the physicians admitted withholding contrast media or premedicating seafood-allergic patients with corticosteroids or antihistamines before the procedure.

Many studies over the past 30 years have failed to find any special relationship between seafood allergy and adverse reactions to radiologic contrast media (RCM). According to some, atopic patients in general may have a fourfold to fivefold increased risk of adverse events in response to RCM. However, the baseline rate of these events is so low that even if these studies were to be confirmed in larger populations, less than 1% of atopic patients would be affected.

About 10 million procedures using RCM are conducted every year in the United States. Life-threatening reactions occur in about 0.2% of patients receiving high-osmolarity contrast media and 0.04% of those getting low-osmolarity contrast media.

The origin of the seafood allergy myth is unknown. But Dr. Beaty, of St. Louis University, has traced it at least as far as a 1975 paper in the American Journal of Roentgenology that stated that 15% of patients who experienced adverse reactions to RCM reported having seafood allergy (Am. J. Roentgenol. Radium Ther. Nucl. Med. 1975;124:145–52). The authors of that study hypothesized that the iodine in seafood cross-reacted with the iodine in RCM. They never verified those patient reports, however, and similar percentages of patients with adverse reactions in their study reported allergies to other common foods such as milk and eggs.

Since then, it has been determined that seafood allergy is mediated by immunoglobulin E (IgE) antibodies to proteins in meat, with iodine playing no role. Furthermore, IgE does not mediate severe RCM reactions. The combination of these two findings effectively discounts the hypothesis of iodine cross-reactivity.

For his study, Dr. Beaty and his colleagues mailed anonymous questionnaires to 231 faculty members at six prominent academic medical centers in the Midwest. Of the individuals queried, 49% responded.

The survey consisted of eight brief questions, but only two of them related to seafood allergy and RCM. The other six were intended as distractors.

The first seafood-related question was, “Do you or someone on your behalf inquire about a history of seafood or shellfish allergy prior to administration of contrast media?” Sixty-five percent of the radiologists and 89% of the cardiologists answered, “Yes.”

The second question was, “Would you withhold RCM administration or recommend pretreatment with corticosteroids and/or antihistamines based on a history of seafood or shellfish allergy?” Thirty-five percent of the radiologists and 50% of the cardiologists answered, “Yes.”

While 69% of the total respondents said that they would ask patients about seafood allergy, only 37% said that they would change management based on that information. That suggests that about 32% would ask the question even if the answer would not affect patient management.

Merely asking that question may serve to perpetuate the myth among patients, Dr. Beaty said. He pointed to a separate study indicating that 65% of patients with seafood allergy had either read or been told by their physician to avoid RCM, and 92% believed that iodine in seafood was responsible for their allergy (Allergy Asthma Proc. 2005;26:468–9).

Several physicians in the audience rose to describe their experiences with this medical myth. One described a radiologic technician who received an official reprimand for failing to ask a patient about seafood allergy. Another physician said that at his institution no allergic patients were allowed to receive RCM unless they were premedicated.

A third physician said that at his institution, the computer system automatically categorized every patient with a seafood allergy as being sensitive to RCM, and every patient who was sensitive to RCM as having a seafood allergy. That has now been changed, but patients who were seen before the change will have that erroneous information persist in their records until someone changes it manually.

Half of the cardiologists in the survey said that they would withhold RCM or pretreat patients with seafood allergies. Lynda Banzi/Elsevier Global Medical News

SAN DIEGO — An old medical myth—that patients who are allergic to seafood are at risk of adverse reactions to radiologic contrast media—persists even among cardiologists, despite having been thoroughly debunked, Dr. Andrew D. Beaty reported at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.

In a survey of 231 specialists at six academic medical centers, 69% of the physicians admitted asking patients about seafood allergy before radiologic procedures using contrast media. Of those surveyed, 37% of the physicians admitted withholding contrast media or premedicating seafood-allergic patients with corticosteroids or antihistamines before the procedure.

Many studies over the past 30 years have failed to find any special relationship between seafood allergy and adverse reactions to radiologic contrast media (RCM). According to some, atopic patients in general may have a fourfold to fivefold increased risk of adverse events in response to RCM. However, the baseline rate of these events is so low that even if these studies were to be confirmed in larger populations, less than 1% of atopic patients would be affected.

About 10 million procedures using RCM are conducted every year in the United States. Life-threatening reactions occur in about 0.2% of patients receiving high-osmolarity contrast media and 0.04% of those getting low-osmolarity contrast media.

The origin of the seafood allergy myth is unknown. But Dr. Beaty, of St. Louis University, has traced it at least as far as a 1975 paper in the American Journal of Roentgenology that stated that 15% of patients who experienced adverse reactions to RCM reported having seafood allergy (Am. J. Roentgenol. Radium Ther. Nucl. Med. 1975;124:145–52). The authors of that study hypothesized that the iodine in seafood cross-reacted with the iodine in RCM. They never verified those patient reports, however, and similar percentages of patients with adverse reactions in their study reported allergies to other common foods such as milk and eggs.

Since then, it has been determined that seafood allergy is mediated by immunoglobulin E (IgE) antibodies to proteins in meat, with iodine playing no role. Furthermore, IgE does not mediate severe RCM reactions. The combination of these two findings effectively discounts the hypothesis of iodine cross-reactivity.

For his study, Dr. Beaty and his colleagues mailed anonymous questionnaires to 231 faculty members at six prominent academic medical centers in the Midwest. Of the individuals queried, 49% responded.

The survey consisted of eight brief questions, but only two of them related to seafood allergy and RCM. The other six were intended as distractors.

The first seafood-related question was, “Do you or someone on your behalf inquire about a history of seafood or shellfish allergy prior to administration of contrast media?” Sixty-five percent of the radiologists and 89% of the cardiologists answered, “Yes.”

The second question was, “Would you withhold RCM administration or recommend pretreatment with corticosteroids and/or antihistamines based on a history of seafood or shellfish allergy?” Thirty-five percent of the radiologists and 50% of the cardiologists answered, “Yes.”

While 69% of the total respondents said that they would ask patients about seafood allergy, only 37% said that they would change management based on that information. That suggests that about 32% would ask the question even if the answer would not affect patient management.

Merely asking that question may serve to perpetuate the myth among patients, Dr. Beaty said. He pointed to a separate study indicating that 65% of patients with seafood allergy had either read or been told by their physician to avoid RCM, and 92% believed that iodine in seafood was responsible for their allergy (Allergy Asthma Proc. 2005;26:468–9).

Several physicians in the audience rose to describe their experiences with this medical myth. One described a radiologic technician who received an official reprimand for failing to ask a patient about seafood allergy. Another physician said that at his institution no allergic patients were allowed to receive RCM unless they were premedicated.

A third physician said that at his institution, the computer system automatically categorized every patient with a seafood allergy as being sensitive to RCM, and every patient who was sensitive to RCM as having a seafood allergy. That has now been changed, but patients who were seen before the change will have that erroneous information persist in their records until someone changes it manually.

Half of the cardiologists in the survey said that they would withhold RCM or pretreat patients with seafood allergies. Lynda Banzi/Elsevier Global Medical News

SAN DIEGO — An old medical myth—that patients who are allergic to seafood are at risk of adverse reactions to radiologic contrast media—persists even among cardiologists, despite having been thoroughly debunked, Dr. Andrew D. Beaty reported at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.

In a survey of 231 specialists at six academic medical centers, 69% of the physicians admitted asking patients about seafood allergy before radiologic procedures using contrast media. Of those surveyed, 37% of the physicians admitted withholding contrast media or premedicating seafood-allergic patients with corticosteroids or antihistamines before the procedure.

Many studies over the past 30 years have failed to find any special relationship between seafood allergy and adverse reactions to radiologic contrast media (RCM). According to some, atopic patients in general may have a fourfold to fivefold increased risk of adverse events in response to RCM. However, the baseline rate of these events is so low that even if these studies were to be confirmed in larger populations, less than 1% of atopic patients would be affected.

About 10 million procedures using RCM are conducted every year in the United States. Life-threatening reactions occur in about 0.2% of patients receiving high-osmolarity contrast media and 0.04% of those getting low-osmolarity contrast media.

The origin of the seafood allergy myth is unknown. But Dr. Beaty, of St. Louis University, has traced it at least as far as a 1975 paper in the American Journal of Roentgenology that stated that 15% of patients who experienced adverse reactions to RCM reported having seafood allergy (Am. J. Roentgenol. Radium Ther. Nucl. Med. 1975;124:145–52). The authors of that study hypothesized that the iodine in seafood cross-reacted with the iodine in RCM. They never verified those patient reports, however, and similar percentages of patients with adverse reactions in their study reported allergies to other common foods such as milk and eggs.

Since then, it has been determined that seafood allergy is mediated by immunoglobulin E (IgE) antibodies to proteins in meat, with iodine playing no role. Furthermore, IgE does not mediate severe RCM reactions. The combination of these two findings effectively discounts the hypothesis of iodine cross-reactivity.

For his study, Dr. Beaty and his colleagues mailed anonymous questionnaires to 231 faculty members at six prominent academic medical centers in the Midwest. Of the individuals queried, 49% responded.

The survey consisted of eight brief questions, but only two of them related to seafood allergy and RCM. The other six were intended as distractors.

The first seafood-related question was, “Do you or someone on your behalf inquire about a history of seafood or shellfish allergy prior to administration of contrast media?” Sixty-five percent of the radiologists and 89% of the cardiologists answered, “Yes.”

The second question was, “Would you withhold RCM administration or recommend pretreatment with corticosteroids and/or antihistamines based on a history of seafood or shellfish allergy?” Thirty-five percent of the radiologists and 50% of the cardiologists answered, “Yes.”

While 69% of the total respondents said that they would ask patients about seafood allergy, only 37% said that they would change management based on that information. That suggests that about 32% would ask the question even if the answer would not affect patient management.

Merely asking that question may serve to perpetuate the myth among patients, Dr. Beaty said. He pointed to a separate study indicating that 65% of patients with seafood allergy had either read or been told by their physician to avoid RCM, and 92% believed that iodine in seafood was responsible for their allergy (Allergy Asthma Proc. 2005;26:468–9).

Several physicians in the audience rose to describe their experiences with this medical myth. One described a radiologic technician who received an official reprimand for failing to ask a patient about seafood allergy. Another physician said that at his institution no allergic patients were allowed to receive RCM unless they were premedicated.

A third physician said that at his institution, the computer system automatically categorized every patient with a seafood allergy as being sensitive to RCM, and every patient who was sensitive to RCM as having a seafood allergy. That has now been changed, but patients who were seen before the change will have that erroneous information persist in their records until someone changes it manually.

Half of the cardiologists in the survey said that they would withhold RCM or pretreat patients with seafood allergies. Lynda Banzi/Elsevier Global Medical News