Selection and evaluation of optimal two‐dimensional CAIPIRINHA kernels applied to time‐resolved three‐dimensional CE‐MRA

Abstract

Purpose To develop and validate a method for choosing the optimal two-dimensional CAIPIRINHA kernel for subtraction contrast-enhanced MR angiography (CE-MRA) and estimate the degree of image quality improvement versus that of some reference acceleration parameter set at R≥8. Methods A metric based on patient-specific coil calibration information was defined for evaluating optimality of CAIPIRINHA kernels as applied to subtraction CE-MRA. Evaluation in retrospective studies using archived coil calibration data from abdomen, calf, foot, and hand CE-MRA exams was accomplished with an evaluation metric comparing the geometry factor (g-factor) histograms. Prospective calf, foot, and hand CE-MRA studies were evaluated with vessel signal-to-noise ratio (SNR). Results Retrospective studies show g-factor improvement for the selected CAIPIRINHA kernels was significant in the feet, moderate in the abdomen, and modest in the calves and hands. Prospective CE-MRA studies using optimal CAIPIRINHA show reduced noise amplification with identical acquisition time in studies of the feet, with minor improvements in the hands and calves. Conclusion A method for selection of the optimal CAIPIRINHA kernel for high (R≥8) acceleration CE-MRA exams given a specific patient and receiver array was demonstrated. CAIPIRINHA optimization appears valuable in accelerated CE-MRA of the feet and to a lesser extent in the abdomen.

Time‐resolved contrast‐enhanced MR angiography with single‐echo Dixon fat suppression

“…Even higher acceleration factors may be possible though the use of CAIPIRINHA‐type sampling (as in Ref. ) and acceleration apportionment which has successfully improved temporal resolution and image quality in time‐subtraction CE‐MRA . Additional performance gains may be achieved in the future by extending this framework and utilizing advanced reconstruction techniques such as nonlinear regularization as in Refs.…”

Recent advances in parallel imaging for MRI

“…Some research has been devoted to choosing an optimal CAIPIRINHA sampling pattern, which depends on scan-specific variables including coil configuration, coil loading, and FOV [122]. Some strategies for determining the best CAIPIRINHA shifts are to create a g-factor map from a low-resolution reference scan or to perform a principal component analysis of the coil sensitivities.…”

Improved receiver arrays and optimized parallel imaging accelerations applied to time-resolved 3D fluoroscopically tracked peripheral runoff CE-MRA

“…Panels (a) and (b) show comparable coronal MIPs from two volunteers, (a) acquired at R = 8 acceleration, and (b) acquired at R = 10 acceleration with a modified CAIPIRINHA undersampling pattern [27], in this case 1 × 10 (7), where this nomenclature represents the R Y × R Z (CAIPIRINHA shift) as described in Ref. [26].…”

“…[8], and also details the improvements afforded by the new receiver coils and parallel imaging technique. Each of three imaging stations (pelvis, thighs, and calves) to be used for fluoroscopic tracking technique was analyzed offline to first determine which strategy, Acceleration Apportionment or optimal CAIPIRINHA, would be utilized for SENSE acceleration optimization, the analysis done using a method described previously [25,27]. For both techniques the optimum acceleration is determined with analysis of the g-factor, a mathematical description of the noise amplification introduced by SENSE acceleration [16], as a predictor of image quality.…”

“…For example, R can be differentially apportioned along the two phase encode directions [25] or alternative undersampling patterns such as Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration (CAIPIRINHA) [26,27] can be applied. It has been shown that optimization of the acceleration apportionment or the CAIPIRINHA sampling pattern can be advantageous for 3D CE-MRA for R ≥ 8 [25,27]. Moreover, the optimization can be performed prior to the actual contrast-enhanced scan and is fast enough to allow practical implementation on a patient-specific basis [25].…”