Detection of renal artery stenosis by means of captopril renal scintigraphy in patients with multiple renal arteries

Interobserver Reproducibility in the Interpretation of Captopril Renograms From Patients Suspected of Having Renovascular Hypertension

This work was undertaken to identify, in hypertensive patients suspected of having renovascular hypertension (RVH), scintigraphic images and curves whose interpretation could be difficult. The baseline and postcaptopril Tc-99m MAG 3 images and curves from 10 patients clinically suspected of having RVH were retrospectively selected to have a wide sample of images and curves. The data and a multiple-choice questionnaire were presented as a PowerPoint file, which was sent electronically to Belgian nuclear medicine physicians; they had to answer if the images and curves were or were not suggestive of the diagnosis of RVH or if it was impossible to answer. There was near-complete interobserver agreement for normal baseline and postcaptopril data, for unilateral postcaptopril delayed transit and/or impaired uptake. Agreement was not as good for bilateral and symmetrical changes, for mild changes, or in cases of impaired function. This study shows that the analysis by the Internet of interobserver agreement is an easy and rapid method allowing one to identify difficult to interpret pre- and postcaptopril renographic data.

Standard dose Gd-DTPA dynamic MR of renal arteries

Renal MR contrast enhancement depends on the timing of image acquisition. Limited human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) administration to demonstrate renal artery stenosis and renal stent patency compared to conventional angiography as the gold standard. Twenty subjects referred for renal angiography underwent 22 dynamic MR studies, including 7 with renal artery stenting (Palmaz P204 or P201, Johnson & Johnson, Sydney, Australia). All were examined with conventional angiography and after dynamic Gd-DTPA infusion. Coronal MR images of the kidneys were acquired using a GE Signa 1.5-T magnet (General Electric Medical Systems, Milwaukee, WI) (fast spoiled gradient echo [FSPGR]; TE=4.2 msec, TR=68-150 msec, flip angle=75 degrees) 0 to 600 seconds after iv bolus injection of 15 ml of Gd-DTPA during sequential breath-hold acquisitions, 13 to 32 seconds each. All 51 renal arteries (13 stenosed, 38 normal) were detected with dynamic MRI. Severity of renal artery stenosis was classified correctly with an accuracy of 98% (95% confidence interval [CI]: 85-100), yielding 98% specificity and 100% sensitivity. All nine renal stents were visualized with 100% accurate patency documentation. FSPGR MRI with bolus Gd-DTPA administration can provide adequate time and spatial resolution to demonstrate renal artery stenosis.

Can the IVIM model be used for renal perfusion imaging?

OBJECTIVE

Renal perfusion imaging may provide information about the hemodynamic significance of a renal artery stenosis and could improve noninvasive characterization when combined with angiography. It was proposed previously that diffusion sequences could provide useful perfusion indices based on the intravoxel incoherent motion (IVIM) model. Owing to motion artifacts, diffusion imaging has been restricted to relatively immobile organs like the brain. With the availability of single-shot echo-planar imaging (EPI) our purpose was to evaluate the IVIM model in renal perfusion.

METHODS AND MATERIAL

Eight volunteers underwent diffusion-sensitive magnetic resonance (MR) imaging of the kidneys using a spin echo (SE) EPI sequence. The diffusion coefficients determined by a linear regression analysis and fits to the IVIM function were calculated.

RESULTS AND CONCLUSION

Our preliminary experience does not support the possibility of obtaining perfusion information using the IVIM model in the kidneys.

The true clinical significance of renography in nephro-urology

Isotopic renography is a non-invasive technique used routinely by the clinician to provide information about kidney structure and function. Whilst there is no doubt of its value in the accurate measurement of glomerular filtration rate and in the detection of parenchymal abnormalities, its role in the diagnosis of renovascular disease (especially in patients with renal insufficiency), the exclusion of obstruction and the evaluation of the patient with either acute renal failure or renal transplant dysfunction remains unproven. In part, this reflects a failure to standardise protocols and rigorously evaluate diagnostic techniques. Recent developments in ultrasound, computerised X-ray tomography and nuclear magnetic resonance now present the clinician with rival techniques and emphasise the need for the clinical development of isotopic renography.