Standardized volume rendering for magnetic resonance angiography measurements in the abdominal aorta

Abstract

Purpose: To compare three methods for standardizing volume rendering technique (VRT) protocols by studying aortic diameter measurements in magnetic resonance angiography (MRA) datasets. Material and Methods: Datasets from 20 patients previously examined with gadolinium-enhanced MRA and with digital subtraction angiography (DSA) for abdominal aortic aneurysm were retrospectively evaluated by three independent readers. The MRA datasets were viewed using VRT with three different standardized transfer functions: the percentile method (Pc-VRT), the maximum-likelihood method (ML-VRT), and the partial range histogram method (PRH-VRT). The aortic diameters obtained with these three methods were compared with freely chosen VRT parameters (F-VRT) and with maximum intensity projection (MIP) concerning inter-reader variability and agreement with the reference method DSA. Results: F-VRT parameters and PRH-VRT gave significantly higher diameter values than DSA, whereas Pc-VRT gave significantly lower values than DSA. The highest interobserver variability was found for F-VRT parameters and MIP, and the lowest for Pc-VRT and PRH-VRT. All standardized VRT methods were significantly superior to both MIP and F-VRT in this respect. The agreement with DSA was best for PRH-VRT, which was the only method with a mean error below 1 mm and which also had the narrowest limits of agreement (95% of cases between 2.1 mm below and 3.1 mm above DSA). Conclusion: All the standardized VRT methods compare favorably with MIP and VRT with freely selected parameters as regards interobserver variability. The partial range histogram method, although systematically overestimating vessel diameters, gives results closest to those of DSA.

MR imaging of aortic coarctation

“…The arrival of contrast material is controlled with real-time imaging (care bolus technique). In patients with GFR <30 ml/min×1.73 m 2 , time-of-flight and phase-contrast sequences can be used, even though image quality is lower and veins are also visualized [47].…”

“…L'acquisizione avviene in apnea, senza sincronizzazione elettrocardiografica, con controllo visuale dell'arrivo del MdC mediante imaging in tempo reale (tecnica care bolus). In caso di GFR <30 ml/min×1,73 m 2 è possibile impiegare sequenze angiografiche senza MdC (time of flight e phase contrast) ottenendo però immagini di qualità inferiore comprendenti anche i vasi venosi [47].…”

Interactive definition of transfer functions in volume rendering based on image markers

“…To overcome this problem, Lundstroem et al [16] utilize partial range histograms to improve tissue classification based on traditional one-dimensional (1D) TFs and add a second dimension to the TF that represents a classification certainty related the shape of specific tissue and its proximity to other tissues. A clinical study demonstrated sufficient accuracy of the approach based on partial range histograms for the assessment of abdominal aortic aneurysms in MR angiography datasets [17]. Lundström et al [18] focuses on 1D TFs but utilizes an alpha histogram that considers spatial coherence to propose useful TF settings.…”