Chapter 6 tion and method of fat-suppression techniques differ between studies. These differences, combined with the fact that most studies included only limited numbers of patients, make it difficult to determine the most optimal MRA protocol. In general, a higher spatial resolution will improve the sensitivity for detecting perforator branches at the cost of longer acquisition times and lower image quality (increased noise-levels). Blood pool contrast agents can be used for steady-state imaging to acquire high-resolution images with excellent signal-to-noise ratios. However, these agents suffer from limited availability and are relatively expensive compared to conventional extra- cellular contrast agents. Acquisition times are longer compared to first-pass imaging sequences using conventional contrast agents. Higher field strength generally provides better signal-to-noise ratios and improved image quality. MRI scanners with field strengths of 3 Tesla or above are less widely available than 1.5 Tesla scanners. In addition, homo- genous fat suppression is much more difficult to obtain at higher field strengths, which could result in unwanted image artifacts or decrease in vessel-to-back- ground contrast ratios, as the perforator branches are located within the subcutaneous abdominal fat. To optimize contrast between the perforator branches and surrounding fat tissue, fat suppression can be very useful. Fat suppression requires a homogenous magnetic field, and is negatively influ- enced by patient movement (breathing and bowel movements), resulting in longer acquisition times. Given these variables, the most suitable MRA sequence to evaluate the perforator branches for each institution will depend on the local availability of MRI hardware, contrast agents and the allowed acquisition time. As an example, the imaging in our institution is in general performed using 15 mL gadobutrol 1.0 mmol/mL (Gadovist®, Bayer Healthcare Pharma- ceuticals), administered through the antecubital vein. An automatic injector is used, ensuring a constant flow rate of 1.5 mL/sec, followed by a saline flush. The field strength of our scanner is 1.5 Tesla and a four-channel SENSE body coil is used for imaging. After the necessary survery and reference scans, we perform several sequences which are listed below. The sequence para- meters of the sequences used in our hospital are also provided. Although these might differ between vendors and field strengths, we think they can serve as a basis for introducing this kind of MR imaging in the reader’s own department. Firstly, the transverse, balanced, T1-weighted FFE is performed, which has a field-of-view of 400x400 mm, and a slice thickness of 6 mm. Voxel size is 1.32 x 1.32 mm. Remaining scan parameters for this sequence are: TE 1.80 ms, TR 3.6 ms, fli p angle 65 degrees (fig 6.5). 95
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