Modified acquisition strategy for reduced motion artifact in super resolution FSE multislice MRI: Application to prostate

Abstract

Purpose To reduce slice‐to‐slice motion effects in multislice T2‐weighted fast‐spin‐echo ( T2 FSE) imaging, manifest as “scalloping” in reformats, by modification of the acquisition strategy and to show applicability in prostate MRI. Methods T2 FSE images of contiguous or overlapping slices are typically acquired using multiple passes in which each pass is comprised of multiple slices with slice‐to‐slice gaps. Combination of slices from all passes provides the desired sampling. For enhancement of through‐plane resolution with super resolution or for reformatting into other orientations, subtle ≈1 mm motion between passes can cause objectionable “scalloping” artifact. Here we address this by subdivision of each pass into multiple segments. Interleaving of segments from the multiple passes causes all slices to be acquired over substantially the same time, reducing pass‐to‐pass motion effects. This was implemented in acquiring 78 overlapped T2 FSE axial slices and studied in phantoms and in 14 prostate MRI patients. Super‐resolution axial images and sagittal reformats from the original and new segmented acquisitions were evaluated by 3 uroradiologists. Results For all criteria of sagittal reformats, the segmented acquisition was statistically superior to the original. For all sharpness criteria of axial images, although the trend preferred the original acquisition, the difference was not significant. For artifact in axial images, the segmented acquisition was significantly superior. Conclusions For prostate MRI the new segmented acquisition significantly reduces the scalloping motion artifact that can be present in reformats due to long time lags between the acquisition of adjacent or overlapped slices while retaining image sharpness in the acquired axial slices.

Model‐based image reconstruction with wavelet sparsity regularization for through‐plane resolution restoration in T2‐weighted spin‐echo prostate MRI

“…The model‐based WS reconstruction method was evaluated in studies in phantoms and humans, the latter performed under an internal review board–approved protocol for which all participants provided written informed consent. Data acquisition used the 2D‐T2SE k Z ‐multislice (KZM) parameters of the prostate MRI study of Kargar et al 35 (Table 1). The TR, TE, and in‐plane resolution were selected to be consistent with the recommendations of PI‐RADSv2.1 16 .…”

“…The PI‐RADS scores as determined from the companion clinical MRI exams were 3 subjects with PI‐RADS 2, 4 with PI‐RADS 3, 5 with PI‐RADS 4, 1 with PI‐RADS 5, and 3 following focal therapy with no applicable PI‐RADS score. For each study reference, TK and WS‐enforced reconstructed stacks of 1‐mm‐thick images were generated, the former using the TK regularization method of Refs26, 35, and 37, and the latter using the aforementioned λ = 0.00015.…”

“…The $$$ {\Delta}_n $$$ operator set contained 24 shifts (6 × 2 × 2 in slice, phase, and frequency). Six slice shifts were used to match the number of distinct groups of slices as defined by their sampling, 35 and were found to provide superior results compared with symmetric (eg, 3 × 3 × 3) neighborhoods. The slice profile B was measured in previous experiments 35 using the same pulse sequence as used in this work.…”

“…Six slice shifts were used to match the number of distinct groups of slices as defined by their sampling, 35 and were found to provide superior results compared with symmetric (eg, 3 × 3 × 3) neighborhoods. The slice profile B was measured in previous experiments 35 using the same pulse sequence as used in this work. The solver was implemented in MATLAB with compiled C ++ code for the lifted wavelet transform.…”

Cross correlation–based misregistration correction for super resolution T2‐weighted spin‐echo images: application to prostate

“…Recently, investigators have explained how motion in multipass multislice acquisition can cause scalloping artifact in reformatted orientations, and furthermore, by segmenting the acquisition it can largely be suppressed. 27 However, this extends the time over which data are acquired for any slice to essentially the entire scan time, increasing the potential for intraslice motion artifact. The goal of this work is to devise a means for correction of scalloping while continuing to limit the acquisition time for any slice to a single pass.…”