Zoomed EPI-DWI of the Pancreas Using Two-Dimensional Spatially-Selective Radiofrequency Excitation Pulses

Abstract

BackgroundImplementation of DWI in the abdomen is challenging due to artifacts, particularly those arising from differences in tissue susceptibility. Two-dimensional, spatially-selective radiofrequency (RF) excitation pulses for single-shot echo-planar imaging (EPI) combined with a reduction in the FOV in the phase-encoding direction (i.e. zooming) leads to a decreased number of k-space acquisition lines, significantly shortening the EPI echo train and potentially susceptibility artifacts.PurposeTo assess the feasibility and image quality of a zoomed diffusion-weighted EPI (z-EPI) sequence in MR imaging of the pancreas. The approach is compared to conventional single-shot EPI (c-EPI).Material and Methods23 patients who had undergone an MRI study of the abdomen were included in this retrospective study. Examinations were performed on a 3T whole-body MR system (Magnetom Skyra, Siemens) equipped with a two-channel fully dynamic parallel transmit array (TimTX TrueShape, Siemens). The acquired sequences consisted of a conventional EPI DWI of the abdomen and a zoomed EPI DWI of the pancreas. For z-EPI, the standard sinc excitation was replaced with a two-dimensional spatially-selective RF pulse using an echo-planar transmit trajectory. Images were evaluated with regard to image blur, respiratory motion artifacts, diagnostic confidence, delineation of the pancreas, and overall scan preference. Additionally ADC values of the pancreatic head, body, and tail were calculated and compared between sequences.ResultsThe pancreas was better delineated in every case (23/23) with z-EPI versus c-EPI. In every case (23/23), both readers preferred z-EPI overall to c-EPI. With z-EPI there was statistically significantly less image blur (p<0.0001) and respiratory motion artifact compared to c-EPI (p<0.0001). Diagnostic confidence was statistically significantly better with z-EPI (p<0.0001). No statistically significant differences in calculated ADC values were observed between the two sequences.ConclusionZoomed diffusion-weighted EPI leads to substantial image quality improvements with reduction of susceptibility artifacts in pancreatic DWI.

Effect of Time-of-Flight Technique on the Diagnostic Performance of 18F-FDG PET/CT for Assessment of Lymph Node Metastases in Head and Neck Squamous Cell Carcinoma

“…Diffusionweighted MR imaging of the head and neck region has been shown to improve the outcome of lymph node staging (3). A new dedicated software application, syngo ZOOMit (Siemens Healthcare), has substantially improved image quality and reduced susceptibility artifacts in pancreatic diffusionweighted MR imaging (4) and has also shown practical potential in the head and neck region because it reduces distortion and better delineates cervical lymph nodes. Although head and neck CT scanning and MR imaging are still considered the standard imaging tests for HNSCC, there has been more evidence suggesting that PET should routinely be added to improve staging of nodal or distant disease, detection of unknown primary lesions, and surveillance for recurrence (5).…”

Feasibility and evaluation of dual-source transmit 3D imaging of the orbits: Comparison to high-resolution conventional MRI at 3T

“…Other groups reported advantages in liver imaging [11] and breast imaging [22]. Dual-source transmission DWI imaging provides benefits in the assessment of phantom experiments [15], the liver [10,11], the pancreas [14,15,23] the spinal cord [12], the prostate [9,24], and head and neck imaging [25]. All these studies report benefits of dual-source transmission in image acquisition of a small region within the body.…”

“…In theory, this approach enables local B1-shimming with more homogenous excitation of the volume of interest, improvement of spatial resolution, and reduction of scan time without foldover artifacts. The pTX technology has recently been reported to increase image quality using the so-called "inner volume imaging" approach [8] in the assessment of several regions, amongst others of the prostate [9], liver imaging [10,11], spine [12,13], and pancreas [14,15]. To our best knowledge, there are no reports of orbital MR imaging using this technique in literature.…”

Comparison of positron emission tomography diffusion-weighted imaging (PET/DWI) registration quality in a PET/MR scanner: Zoomed DWI vs. Conventional DWI

“…The recent development of parallel radiofrequency (RF) transmitters has enabled independent transmission of RF power over multiple channels, which allows the use of spatially selective RF pulses to excite only those protons inside the field of view (FOV), as well as permitting the FOV to be narrowed along the phase‐encoding direction without the risk of aliasing artifacts . With this technique, called zoomed DWI, DWI distortion can be minimized with no influences from adjacent tissue along the phase‐encoding direction …”

“…[13][14][15] With this technique, called zoomed DWI, DWI distortion can be minimized with no influences from adjacent tissue along the phase-encoding direction. [16][17][18] The aim of this study was to compare zoomed DWI (z-DWI) with conventional DWI (c-DWI) with regard to registration quality of images produced by a PET/MR scanner in patients with malignant tumors.…”