Role of Multidetector Computed Tomographic Angiography In Evaluation of Renovascular Hypertension

Abstract

Contrast enhanced multidetector computed tomographic angiography (MDCTA) is fast, reliable and non-invasive modality which provides accurate anatomic images of the renal arteries with multi-detector-row helical scanners permitting acquisition of isotropic datasets that enable the reconstruction of high resolution images in any plane. Advantages compared to DSA include less invasiveness, faster acquisitions, and multiplanar imaging. As with conventional angiography, the disadvantages of this technique are its ionizing radiation and its use of nephrotoxic contrast material. The recent introduction of MDCT has considerably shortened acquisition times of increasingly large volumes with excellent spatial resolution, which allows for high quality multi planar and volume rendered reconstructions, reduced contrast material, with excellent depiction of small vessels, including accessory arteries and segmental branches without opacification of the renal veins MDCT can yield high quality vascular images that can be reconstructed in two and three dimensional angiograms. Not only the number, size, course and relationships of the renal vessels can be easily demonstrated by using real-time interactive editing of these reconstructions, but also CT can identify calcifications, post-stenotic dilatation and parenchymal abnormalities such as infarction and atrophy The increased speed of scanning and faster CT table speeds allow more imaging details with a single injection of intravenous iodinated contrast material. It also improved the visualization of distal renal arteries and has led to improved contrast efficiency and decreased radiation exposure. Single breath-hold image detection is a significant improvement with MDCT compared to the longer breath holds required for SDCT (single detector computed tomography).

Careful selection of CT scanning protocols is needed to keep the radiation exposure ‘As Low As Reasonably Achievable’ (ALARA). ALARA principle emphasizes the need to perform justifiable CT scans with the minimum radiation dose necessary to meet clinical and diagnostic objectives MDCT uses a smaller amount of contrast material than single slice CT. CTA was performed without any major side effects, results of serum creatinine levels 3 months' post CTA were analyzed and showed no clinically important increase greater than 0.1 mg/dL. Normal results from MDCTA virtually rule out renal artery stenosis. Both maximum intensity projection (MIP) and volume-rendering techniques are useful and complementary in CT evaluation of renal artery stenosis. Secondary signs include post stenotic dilatation, renal atrophy, and decreased cortical enhancement. A threshold of 800 mm2 for cortical area and 8 mm for mean cortical thickness seen on CT can be useful morphologic markers of atherosclerotic renal disease.