Lower-extremity CTA

Lower-extremity CTA has evolved into an accurate, robust, and widely available test for noninvasive imaging of the peripheral arterial tree, for a wide range of clinical indications congenital abnormalities (e.g., popliteal entrapment syndrome), vascular (iatrogenic and non-... 

The purpose of this chapter is to review the practical aspects of state-of-the-art lower-extremity CTA in its role as a treatment-planning tool for patients with PAOD. Taking full advantage of the capabilities of lower-extremity CTA in this role requires integration of acquisition and contrast medium injection parameters, with knowledge of therapeutic options and the ability to vi-... 

Lower-extremity CTA can be performed with all currently available MDCT scanners. No special hardware is required. Because of the slightly thicker sections (2.5-3 mm) usually obtained with four-channel MDCT (4 X 2.5 mm), evaluation of crural and pedal arteries is slightly limited, notably if calcifications are present. The technical limitations of four-channel MDCT are only clinically problematic in a small subset of patients, such as individuals with critical limb ischemia who have no or mild inflow and femoropopliteal disease, and who have diseased and calcified infrapopliteal vessels. In the majority of patients—notably those with intermittent claudication where interventions are limited to aboveknee arteries—even four-channel MDCT can provide all the therapeutically relevant information (Heijen-brok-Kal et al. 2007 Rubin et al. 2001 Ofer et al. 2003 Martin et al. 2003 Ota et al. 2004 Catalano et al. 2004). 

The technique of contrast medium injection always needs to be adapted to the scanner capabilities, but in the setting of lower-extremity CTA, also to the contrast medium flow dynamics. In patients with PAOD, the intravascular propagation of an intravenously injected contrast medium bolus may be substantially delayed within the dieseased lower extremity arterial tree. We have observed that the aortopopliteal bolus transit speed may be as slow as 30mm/s (Fleischmann and... 

The delayed flow dynamics in a diseased arterial tree therefore prohibit the use of the maximum scanning speed that is available with modern CT scanners. Our strategy for an integrated 64-channel lower-extremity CTA acquisition and injection protocol therefore uses an intentionally slow acquisition time of 40 s in all patients, which is combined with a 35-s injection duration in all patients (Table 25.2). Note, that the injection duration can be 5 s shorter than the scan time, because the scan follows the bolus down the peripheral arte-... 

Table 25.3. Standard set of postprocessed images for lower-extremity CTA (DICOM series)...

Fig. 25.5. Lower-extremity CTA in a 84-year-old woman with biiateral calf claudication, left greater than right. MIP shows significant caicifications in the right common femoral artery ([CPA] arrow) and in the proximai SPA arrowhead), as well as in the biiaterai distai SPA/popliteai arteries, respectively. Note, that the calcifications do not allow evaluation for the presence/ degree of arteriai stenoses. MpCPRs in anteroposterior and right anterior obiique views cieariy demonstrate the extent of...

The presence of the PMMA or PET lowers the criticd concentration of the CTA. For example, a 19.6/1.2/70.2 (w/w/w) ternary solution of CTA, PMMA and TFA-CH2CI2 (6 4 v/v) and an 18.6/1.2/80.2 ternary solution of CTA, PET and TFA-CH2Q2 (6 4 v/v) were biphasic when viewed under crossed polars. Each solution appeared to be one ph but a small isotrq>ic phase may have been present, a required an extremely long time to separate due to the high viscosity of the anisotropic matrix. 

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