Gadodiamide administration causes spurious hypocalcemia, particularly at doses of 0.2 mmol/kg or higher and in patients with renal insufficiency.
For time-resolved background-subtracted contrast-enhanced magnetic resonance angiography, the bright and sparse arterial signal allows unique identification of contrast bolus arrival in the arteries. This article presents an automatic filtering algorithm using such arterial characterization for selecting arterial phase images and mask images to generate an optimal summary arteriogram. A paired double-blinded comparison demonstrated that this automatic algorithm is as effective as the manual process.Magn Contrast-enhanced magnetic resonance angiography (CEMRA) has become a routine clinical tool for pretreatment mapping of vasculature (1). Among data acquisition techniques for CEMRA, the time-resolved strategy offers a very useful option for many situations because of the elimination of the cumbersome timing of imaging to the contrast bolus arrival (2-13). The time-resolved CEMRA generates time series images in a manner similar to fluoroscopic X-ray angiography, where image postprocessing has been used frequently to improve vasculature display (14,15). For example, from the time-series images all mask images and arterial phase images can be summoned into one image of greater vascular detail with high signal-tonoise ratio (SNR) that is particularly useful for presentation in a surgical operation room where video display may not be available. Linear filtering techniques such as the matched filters can be used to produce a summation image (15,16) and have been attempted in time-resolved or dynamic CEMRA to generate a summary arteriogram (17-21). In practice, the major challenge for summarizing time series images is to identify the contrast bolus arrival and to avoid motion-corrupted mask images and arterial phase images that propagate severe motion artifacts into the final summation image (21). So far, this avoidance of motioncorrupted images and selection of optimal arterial phase and mask images for summation have been performed through a tedious manual procedure (21).Here we report an algorithm that can fully automate the linear filtering process, i.e., to select the set of arterial phase images and the set of mask images such that the subtracted image from the former to the latter is of the best quality. We describe in detail 1) how to quantify the notion of "image quality," and 2) how to effectively select the mask and arterial phase images based on the quantified measure of quality. POSTPROCESSING TECHNIQUES Problem StatementOur approach is basically an automated version of linear filtering that selects a mask image set and an arterial phase image set to generate a linear filtered image. For a given time series of images (I n , n ϭ 1ϳ n max , n max ϭ 35 -40, the total number of images in the time series), indexed by x and y, we want to select the mask image set (M) and the arterial phase image set (A), such that the subtracted or filtered image (S h ) is of "best quality," where S h is given by:where ͉M͉ and ͉A͉ are the number of mask images and arterial phase images, respectively. Note that all the arithmetic ...
The authors report the case of a 54-year-old man with intermittent claudication secondary to adventitial cystic disease of the popliteal artery. This uncommon cause of claudication is discussed along with its diagnostic features.A 54-year-old man with no risk factors for vascular disease presented with the diagnosis of unilateral intermittent claudication in his right calf region with absent foot pulses. His claudication had worsened during the course of the last 6 months, with an absolute claudication distance of approximately four blocks (equivalent to approximately 320 m). He denied knee discomfort and had sustained no recent injury to his knees. There was no occupational history suggestive of repetitive trauma to the knee. Axial magnetic resonance imaging (MRI) of the right knee showed proton density (Panel A) and fat-saturated (Panel B) T2-weighted images revealing cysts in the wall of the popliteal artery with luminal narrowing (see arrows). Gadoliniumenhanced 2D projection MR angiography con rmed the presence of a 50% diameter stenosis. Panels C and D are coronal and sagittal images, respectively, showing smooth tapering of the vessel lumen (see arrows) caused by concentric compression. The vessel above and below the focal stenosis is widely patent without evidence of thrombus formation or atherosclerotic disease.The condition of cystic medial necrosis of the knee predominantly affects males (sex ratio 15:1) in their fourth and fth decades. The popliteal artery tends to be the most common location (. 90%), followed by the femoral and external iliac arteries (9%), and rarely arteries in the upper extremity. The enlargement of cyst(s) in the artery wall results in progressive unilateral claudication and additionally may cause ischemic neuropathy-like symptoms such as paresthesia and burning pain in the lower extremity. MR techniques offer the advantage of providing angiographic information on lumen encroachment as well as data on the actual size and location of the cysts and are therefore advantageous in the diagnosis of this condition.
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