VIENNA - With digital subtraction angiography on the wane, a variety of newer techniques are elbowing for respect in the evaluation of atherosclerosis and stenosis. Ultrasound is showing unique strengths in plaque characterization within vessel walls. Multislice CT is doing an excellent job of evaluating vessel morphology, especially when calcium doesn't get in the way, and radiologists appreciate its ability to pick up unsuspected pathology.
Meanwhile MR angiography, an emerging favorite at ECR 2002, just keeps getting better. In a presentation in today's scientific sessions, Dr. J. G. Houston, a radiologist with Ninewells Hospital and Medical School in Dundee, UK, discussed the role of MRA-imaged blood flow changes as a predictor of disease.
"We know that in patients with significant stenosis, greater than 60%, a certain high percentage progress to perfusion in two years," Houston said. "What we don't know are which ones will progress, and that's really what this talk is about."
Houston and colleagues have been looking at blood flow patterns and the fluid dynamics of stenosis in an effort to predict the progression of renal artery stenosis and renal failure.
"It may not be known widely that although it's accepted that blood flow in arteries is linear and laminar, in other words it goes straight down, there is increasing evidence that that's not strictly the case," he said. "In young people in particular who are not diseased the flow pattern is linear, and laminar, and spiral too."
There are simple methods of looking at it, he said, such as in angioscopy of the popliteal arteries, where one can get the impression that a rotation in blood flow is occurring. In MR angiography using a marking technique, the flow into the plane is visualized as white, and the flow out is black, enabling consistent detection of secondary blood flow patterns which could indicate progressive stenosis.
"The aim of this work has been to establish a relationship between spiral aortic blood flow patterns and renal function in relation to renal artery stenosis," Houston said.
The study evaluated 86 patients with chronic renal failure who were imaged using a standard 3-D contrast-enhanced MR angiography technique.
Three-dimensional MRA images were acquired on a 1.5-tesla Siemens Medical Solutions Symphony scanner. Images were acquired in the oblique coronal plane (TR 4.0, TE 1.65 msec, slice thickness 1 to 1.2 mm). ECG gating at 75% of R-R was used, and each scan took approximately 7 minutes. Postprocessing was performed with Siemens' standard software package and with Voxar software. The software was used to create MIPs and MPRs used to detect the spiral flow.
Renal artery stenoses were characterized as unilateral or bilateral, and characterized as mild (<60%) or severe (>60%). Renal function was followed up between 9 and 12 months post-imaging. A quarter of the patients were also hypertensive, and 32% were diabetic.
According to the results, 33 patients (20 male and 13 female) showed significant renal artery stenosis of >60% at the time of imaging. Fourteen of the patients demonstrated aortic spiral blood flow and 19 did not.
During follow-up 16 (48%) patients had significant short-term deterioration in renal function, with a mean creatinine rise of 55 mmol/l. Only 4 of the 14 patients with spiral flow detected at MRA showed deteriorated renal function at follow-up, with a mean creatinine rise of 55 mmol/l. Patients in whom spiral flow had not been detected fared worse. Among these patients, 12 of 19 (63%) showed a significant deterioration in renal function, with a mean creatinine rise of 102 mmol/l. The rising creatinine in the two groups was significantly different (p=0.048).
Thus, patients with spiral flow deteriorated less over the follow-up period than those in whom spiral flow could not be detected, Houston said. The prevalence of spiral flow was affected by severity of arterial stenosis. The assessment of spiral flow with MRI is feasible in clinical practice, Houston concluded.
"Spiral flow is associated with a lack of disease, and a lack of spiral flow is associated with severity of renal impairment progression as measured by renal artery stenosis. We believe it may be a factor in renal impairment progression in patients with ARVD (atherosclerotic renovascular disease)," he said.
By Eric Barnes
AuntMinnie.com staff writer
March 2, 2002
Related Reading
ICA imaging differentiates total versus near total occlusion, January 8, 2002
MRI, MRCP and 3-D MRA separate pancreatitis from cancer, November 26, 2001
Contrast-enhanced MR angiography effective for evaluating cervical vessels, October 10, 2001
AngioSURF rides new wave in MR angiography, April 11, 2001
Renal MRA studies change treatment plans, March 7, 2001
Copyright © 2002 AuntMinnie.com
