March 21, 2012
The constraint: Some obese patients are too large to image using even X-ray films of large size. They need multiple cassettes. Photo: AFP
Keen observation and analysis of case sheets of patients proved rewarding for Dr Raul Uppot, a young radiologist at the Massachusetts General Hospital (MGH), in Boston, U.S. He realised that a tiny fraction of patients are denied medical imaging facilities simply because they are bulky. Radiologists could not provide optimum image quality and accurate diagnoses in their cases.
Dr. Uppot and his co-workers reviewed the radiology reports filed between 1989 and 2003 labelled as “limited by body habitus” meaning limited in quality due to the patient’s size. They found that over the 15-year period, the percentage of such reports nearly doubled from 0.10 in 1989 to 0.19 in 2003. It correlated strongly with the increase in obesity in Massachusetts State from 9 per cent in 1991 to 16 per cent in 2001.
He presented the study at the annual meeting of the Radiological Society of North America (RSNA-2004). RSNA appreciated his paper and awarded him the 2004 Research Fellow Trainee Prize of $ 1,000.
Dr Uppot observed that in the 15-year-old retrospective study of radiological exams at MGH, the diagnostic information of 0.15 per cent of the five million studies was limited by the body weight of patients. They did not include patients whose examinations were cancelled because they could not fit on the table.
Obesity adversely impacts on simple x-ray and other life saving procedures such as CT scans, ultrasound and magnetic resonance imaging (MRI).
The issue was so important that the RSNA held a special focus session on “Obesity: The Impact on Radiology” during its Annual convention (RSNA 2005) at Chicago. It continues to be important.
In a recent review in Vascular Medicine (December 2011) Philip C. Hawley of the Grant Medical Centre, Columbus and Miles P. Hawley, The Ohio State University Medical Center, Columbus, recommended further research on both imaging and outcomes in the area.
In Radiology Rounds, a newsletter for Referring Physicians, published by Massachusetts General Hospital, Janet Cochrane Miller noted that fat affects ultrasound images to a greater degree than any other medical imaging modality. At the frequency range normally used (3 to 7 MHz) for abdominal imaging, one cm of fat attenuates 50 per cent of the beam intensity. At lower frequencies attenuation is less; image resolution is also less.
Miller estimated that 20 patients in 1,000 may not get the benefit of ultrasound scans because of excess body weight. Corresponding data for MRI scan is one in 1,000; abdominal CT: 4 in 1,000; chest x-ray: 5 in 1,000.
Some obese patients are too large to image using even x-ray films of large size. They need multiple cassettes. “When they exceed the weight limit for x-ray tables, patients can sometimes be imaged while standing”, Miller wrote.
To a question whether he expects that the issues he raised in the U.S. will be applicable to India, Dr Uppot who is currently assistant professor, Harvard Medical School, clarified that the issues start with ultrasound imaging at 250 pounds.
“Census data in India may need to identify the percentage of Indians who reach more than 250 pounds”, he added.
Relevance to India
“Has he got any suggestions for the Indian medical community? “The Indian medical community should be aware of the issue. In India, as in other Asian and European countries there is great reliance of ultrasound for medical imaging.
Of all the imaging modalities, ultrasound is the most sensitive to obesity. Indians who have excessive subcutaneous fat will present challenges to physicians who rely on ultrasound to make diagnosis”.
To the query on improvements in producing optimal images of obese patients, Dr Uppot stated that “manufacturers of imaging equipment have tried to address the issue by: (1) Increasing weight limits and gantry/bore diameters of their equipment so that patients can fit. (2) Used technology to improve the image quality such as harmonic imaging for ultrasound and (3) and used technology to try to decrease the increased radiation doses for CT in obese patients”.
The Lancet (November 20, 2010) reported that currently in India, almost 1 in 5 men and over 1 in 6 women are overweight. In some urban areas, the rates are as high as 40 per cent. But I do not know of any Indian publication on the difficulties of imaging obese patients.
The medical community in India must appreciate the issues and be prepared to face the challenges of imaging overweight patients
Raja Ramanana fellow, Department of Atomic Energy