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Focus on Imaging |
1 From the Departments of Radiology (M.H.S.) and Medicine (G.S.), Vanderbilt University Medical Center, 21st Ave and Garland St, Nashville, TN 37232. Received February 21, 2001; accepted February 27. Address correspondence to M.H.S. (e-mail: marta.schulman@mcmail.vanderbilt.edu).
Index terms: Focus on Imaging • Kidney, CT, 81.1211 • Kidney, MR, 81.1214 • Kidney, US, 81.1298
EDITOR’S NOTE: The first Focus on Imaging article was entitled "Focus on Imaging at the American Heart Association Annual Meeting" (Radiology 2000; 216:323–324). Our readers are referred to this publication for information regarding the type of material that will be published in this section of the Journal.
Anthony V. Proto, MD, Editor
The American Society of Nephrology (ASN) held its 33rd annual meeting in Toronto, Ontario, Canada, October 11–16, 2000. The meeting was a conjoined congress of the ASN and the International Society of Nephrology and, as such, hosted a large international attendance. The meeting was attended by over 11,000 registrants; of these, approximately 9,000 were medical personnel and approximately 2,000 were exhibitors or other supporting staff. Nearly 6,000 attendees were U.S. residents, while the remainder represented an international community of 89 countries, from American Samoa to Taiwan.
The ASN consists of approximately 7,500 members from over 65 countries, indicating the international representation of the specialty within the society. Of the members, 91% hold MD degrees, 13% hold PhD degrees, and 7% hold both. More than 70% have an academic appointment, 66% conduct clinical research, and 47% are involved in basic laboratory research. Adult nephrologists compose 86% of the membership, and 71% describe adult nephrology as their primary specialty. The ASN holds several postgraduate education and self-assessment programs in conjunction with the National Kidney Foundation and supports various awards, including the Homer W. Smith Award, the John P. Peters Award, and the Research Scholar and Young Investigators Award, to recognize excellence in the field. The ASN supports career enhancement and research fellowships to promote ongoing investigations in the specialty.
The congress consisted of several sections. Review and hands-on courses were held during the first 2 days of the meeting. The scientific program included abstracts on ongoing research by the membership, as well as didactic lectures by experts in their fields. The premises accommodated large spaces for both scientific exhibits and corporate exhibitors, who displayed state-of-the-art clinical equipment. Featured among these were several ultrasonography (US) machines, including handheld models that are particularly useful in vascular access procedures such as insertion of central catheters. Also prominently featured were various units that calculate volume flow through dialysis shunts by using dilutional principles and Doppler US signals under conditions of variable flow. Digital mobile radiographic imaging systems were also featured among the exhibits by corporate vendors.
Of a total of 3,964 scientific abstracts, approximately 80 addressed some aspects of imaging techniques. The predominant modality was US, with a smaller role played by computed tomography (CT) and magnetic resonance (MR) imaging.
US Imaging
US was featured prominently in all aspects of the congress. A 2-day curriculum course outlined the basics of US as applied to renal imaging, renal biopsy, and vascular access evaluation and featured a hands-on component for participants. One course addressed new imaging techniques in nephrology. During the section on US, the role of the modality was discussed with regard to determination of various causes of acute and chronic renal failure, renal artery stenosis, renal vein thrombosis, and the role of the resistive index in native and transplanted kidneys.
In the scientific presentations, many topics were discussed, outlining US as it applies to the evaluation of the kidney in health, disease, and secondary conditions that accompany renal disease. Approximately 15 presentations dealt with the evaluation of vascular access with various Doppler US techniques designed to determine access flow as an indicator of access patency. Results reported in the majority of these presentations corroborated the accuracy of dilution techniques and the high correlation between blood flow of less than 500 mL/min and subsequent access failure. Other presentations compared the accuracy of color Doppler US techniques, variable flow techniques, and glucose infusion techniques in the assessment of access volume flow.
In approximately nine presentations, US was used to demonstrate findings suggestive of peripheral vascular disease in patients with renal failure of various causes and under various forms of treatment in both children and adults. These studies focused on plaque formation in the carotid and lower limb arteries, as well as on evaluation of endothelial function. Endothelial dysfunction has been implicated in the accelerated development of atherosclerosis and is assessed by determining a normal increase in the diameter of the brachial artery in response to ischemia, but not to nitroglycerin, as the inciting stimulus.
In a small number of papers, presenters evaluated Doppler US indices and velocity values in the evaluation of patients with renal artery stenosis before and after surgery. Several abstracts included discussion of morphometric renal data as an indicator of renal abnormalities: autosomal-dominant polycystic renal disease at differing genetic loci, renal size and shape vis-à-vis body size, and acute tubular necrosis versus prerenal azotemia. One group of investigators developed a computerized model of renal echogenicity to quantify differences with respect to the liver as a reflection of medical renal disease. Bone US, broadband US attenuation, and speed of sound were also discussed in the context of quantifying bone mineralization in patients treated with hemodialysis, as correlated with parathyroid hormone, alkaline phosphate, and vitamin D levels. Finally, the role of US in invasive procedures, including renal biopsy with US guidance by the nephrologist, and the various complications of biopsy with US and CT guidance were also part of this diverse group of presentations involving US.
CT Imaging
The use of CT was comprehensively described in the course on new imaging techniques in nephrology. The advantages of CT urography over intravenous pyelography were described, including the superiority of CT with regard to detection of urolithiasis, detection and characterization of renal masses, and, with volumetric acquisition, ability to obtain delayed images and coronal reconstructions that permit examination of the urothelium and essentially eliminate the need for conventional radiographic excretory urography.
Several presentations involving the use of CT converged on the detection of coronary artery calcifications in patients with end-stage renal disease and the correlation of calcifications with the duration of dialysis and the presence of carotid plaque. CT compared favorably with US in the detection of pyelonephritis and its complications in another study.
Helical contrast agent–enhanced CT was found to be equal to or better than angiography for the preoperative evaluation of noncadaver donor kidneys. Contrast-enhanced CT was used to assess renal perfusion in a hypercholesterolemic animal model. Renal biopsy with CT guidance was not found to offer any increase in safety margin over conventional biopsy with US guidance. CT was also discussed as a sensitive method to detect mesenteric ischemia in patients undergoing dialysis who have abdominal pain; the case-control study investigators found a preponderance of right-sided colonic and cecal involvement in these cases and described a link between expediency of diagnosis and patient outcome.
MR Imaging
The course on new imaging techniques described the utility of MR imaging, defined in terms of both anatomic depiction and angiographic evaluation of the kidneys and related abdominal vascular structures, including the inferior vena cava and aorta. The discussant described the various MR pulse sequences and angiographic techniques and demonstrated examples of the utility of the modality in demonstrating aortic pathologic conditions such as aneurysms and dissections, renal vascular conditions such as renal artery stenosis, and vascular conditions that develop in renal transplants.
Presenters described the utility of MR imaging in assessing renal cortical volume, which was then extrapolated to determine the number of glomeruli as calculated with preceding biopsy specimens from transplanted kidneys. Cardiac output and ventricular mass measurements were also obtained in patients being treated with hemodialysis and in healthy control subjects. MR imaging was also performed in young patients with autosomal-dominant polycystic kidney disease and was used to determine that renal blood flow is decreased in these patients, as correlated with renal volume, creatinine clearance, and blood pressure. MR imaging, with heavy T2 weighting, was also found to be more sensitive than US for the detection of autosomal-dominant kidney disease, which is of particular importance in the screening of living related donors in these patients.
Synopsis of New Imaging Approaches
US is being applied to the detection of cardiovascular disease by means of evaluation of carotid and peripheral vessels and assessment of endothelial function under various clinical and experimental conditions. Acoustic impedance and sound velocity are being used in the noninvasive determination of bone mineral content. Quantitative volume flow through various types of hemodialysis access shunts is being evaluated as a determinant of impending access failure and the need for preemptive intervention. Volumetric CT and MR imaging are being applied in the assessment of renal perfusion and quantification of cortical and glomerular mass.
Summary
Although a relatively minor focus of the meeting, imaging techniques—particularly US—found an important niche in the diagnostic and therapeutic armamentarium of the clinical nephrologist. Increasingly, these techniques are being applied in experimental protocols to assess the in vivo effects of chronic renal failure and its multisystemic consequences.
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