Doppler ultrasound offers a convenient way for practitioners to do bedside imaging on patients with acute renal failure, without having to take blood or urine samples, according to Japanese researchers.
In a study published in the April 2000 issue of the American Journal of Kidney Diseases, internal medicine specialists from Osaka University used Doppler ultrasound to differentiate between acute tubular necrosis (ATN) and pre-renal azotemia.
"Urinary diagnostic indices, including urinary sodium, fractional excretion of sodium (FENa) and renal failure index (RFI) ... often cannot be used in acute renal failure (ARF) when patients have complete anuria, after diuretic use, or after hemodialysis. A rapid and reliable discrimination index between ATN and pre-renal azotemia would be highly valuable at the bedside," the authors wrote (AJKD, April 2000, Vol. 35:4, pp. 713-719).
To that end, the group evaluated 40 patients with ARF with Doppler ultrasound. A real-time ultrasound unit with color Doppler and a 3.5-MHz convex-type probe was used to image the intrarenal arteries; pulsed Doppler ultrasound was used to evaluate the blood-flow velocities of segmental arteries. The resistive index (RI) and pulsatility index (PI) were calculated to assess renal vascular resistance.
At the onset of ARF, 16 patients had RI and PI values within the normal range but a FENa measurement of less than 0.4% and an RFI of less than 0.1, indicating pre-renal azotemia. Among the other 24 patients, all but two had RI and PI above the normal range, suggesting increased vascular resistance. With a FENa measurement of greater than 4.7% and RFI that was greater than one, these patients most likely had ATN, the authors stated.
"Doppler ultrasound is a non-invasive way to measure intrarenal blood flow and flow velocity," the paper concluded.
In other radiology news, researchers from the departments of nuclear medicine, pathology, and dermatology at a German institution banded together to evaluate a staging technique for assessing primary cutaneous melanoma in patients with skin cancer. The results of their study appear in the April 2000 issue of the Journal of Investigative Dermatology.
Conducted at Eberhard-Karls University in Tuebingen, the study used a variety of imaging techniques to aid in the detection of submicroscopic melanoma cells in sentinel lymph nodes (J Invest Dermatol, April 2000, Vol.114:4, pp.637-642).
First, a sentinel lymph node biopsy was performed in 116 patients with primary cutaneous melanoma. The patients then were evaluated with lymph node ultrasound, a chest x-ray, abdominal ultrasound, and CT to rule out metastatic melanoma in distant sites.
Cutaneous lymphoscintigraphy was done preoperatively to identify nodal basins at risk for metastatic melanoma. Lymphatic mapping was performed intraoperatively by a hand-held gamma probe to find radiolabeled nodes.
According to the results, sentinel lymph node biopsy and lymphatic mapping was successfully performed in 96% of the patients. Lymph nodes were obtained and analyzed by histopathology. During a 19-month follow-up, 20% of the 116 patients developed recurrent disease. Follow-up examination consisted of an ultrasound exam of the lymph node basins and abdomen, and CT and MRI exams in those patients with possible recurrent metastatic melanoma.
Finally, imaging played a significant role in several studies published in the March 28, 2000 issue of Circulation:
- Using intravascular ultrasound and Doppler flow, cardiologists at Stanford University Medical Center assessed the relationship between coronary remodeling and transplant allograft vasculopathy (TxCAD). They hoped to gain insight into how coronary remodeling affects lumen loss in TxCAD. One artery in each of 27 transplant patients was investigated with simultaneous intravascular ultrasound and flow measurements were taken with a Doppler flow wire. The team concluded that vessel remodeling in TxCAD is greater in eccentric lesions than in concentric lesions (Circulation, March 2000, Vol.101:12, pp.1384-1389).
- French researchers tested the accuracy of color M-mode tissue Doppler imaging to characterize normal, ischemic, and stunned myocardium, as well as assess non-uniform transmural myocardial velocities. In this study conducted at the Hopital Charles Nicolle in Rouen, 13 open-chest dogs underwent left anterior descending coronary artery occlusion followed by reperfusion. M-mode tissue Doppler imaging was obtained from an epicardial short-axis view. The modality was able to depict endocardial velocities, systolic velocities, and segment shortening. The group concluded that tissue Doppler imaging shows promise as a tool for quantifying ischemia-induced, regional, myocardial dysfunction (pp.1390-1395).
- MRI proved successful for the detection of significant coronary artery stenosis in a prospective study done by German cardiologists. The group from the German Heart Institute and Charite at Humboldt University in Berlin imaged 15 patients with single-vessel coronary artery disease, as well as five healthy patients. MR was able to gauge a significant difference in myocardial perfusion reserve between ischemic and normal myocardial segments, with a sensitivity of 90%, a specificity of 83%, and an accuracy of 87%. (pp.1379-1383).
By Shalmali Pal
AuntMinnie.com staff writer
April 24, 2000
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