Optimized workflow and imaging protocols for whole-body oncologic PET/MRI

Abstract

Although PET/MRI has the advantages of a simultaneous acquisition of PET and MRI, high soft-tissue contrast of the MRI images, and reduction of radiation exposure, its low profitability and long acquisition time are significant problems in clinical settings. Thus, MRI protocols that meet oncological purposes need to be used in order to reduce examination time while securing detectability. Currently, half-Fourier acquisition single-shot turbo spin echo and 3D-T1 volumetric interpolated breath-hold examination may be the most commonly used sequences for whole-body imaging due to their shorter acquisition time and higher diagnostic accuracy. Although there have been several reports that adding diffusion weighted image (DWI) to PET/MRI protocol has had no effect on tumor detection to date, in cases of liver, kidney, bladder, and prostate cancer, the use of DWI may be beneficial in detecting lesions. Another possible option is to scan each region with different MRI sequences instead of scanning the whole body using one sequence continuously. We herein report a workflow and imaging protocols for whole-body oncologic PET/MRI using an integrated system in the clinical routine, designed for the detection, for example by cancer screening, of metastatic lesions, in order to help future users optimize their workflow and imaging protocols.

A practical approach to optimize scan protocol for simultaneous whole-body positron emission tomography/magnetic resonance imaging in cancer staging

“…This adopted time efficient PET/MRI whole-body protocol and regional study as per clinical need is similar to reported earlier[ 5 6 ] but were different in terms of MR sequence type along with selective imaging planes.…”

“…The present protocol acquires images in axial orientation to cover the whole body in matching slices with optimized T1 TFL sequence for T1 contrast, STIR for T2 contrast, diffusion (with different b values), and fat-suppressed postcontrast (VIBE) images in addition to PET for spatial correlation of tissue parameters to assess the nature of a lesion which is distinct from reported by others. [ 5 6 ] Such an approach greatly helps in the correct classification of a nonmetastatic marrow lesion from a true metastatic one as seen in Figure 3 , thus improving staging accuracy impacting clinical management. Acquiring in the axial plane through optimized sequences avoided bias induced in the localization of lesions when images are read in rather different planes with an objective to reduce imaging time.…”

“…No standardized imaging protocol is available till date and workers in this field have reported different approaches such as limiting number of MR sequences in the whole-body mode to keep the examination time short. [ 5 6 7 ] Well-tailored imaging protocols should include time-optimized range of MR sequences to effectively complement and supplement PET and vice versa to increase efficacy of “M” staging. Appropriate selection of tissue-specific radiotracers could also save time while enhancing utility of this combined modality in staging cancer.…”

Performing clinical 18F-FDG-PET/MRI of the mediastinum optimising a dedicated, patient-friendly protocol

“…However, in this study, no contrast agent was used and the addition of SPAIR did not significantly affect SNR and contrast between tumours, LN, and surrounding tissue. Nevertheless, unenhanced T2-HASTE sequences have been reported to sensitively detect pleural effusion and intra-atelectatic tumour growth [9,20,21]. The effect of motion and MR motion-correction was less prone on PET-images, although motion has a negative effect on the localisation of PET-signal.…”

MR Imaging in the 21st Century: Technical Innovation over the First Two Decades

“…With advances in semiconductor photon detection devices, integrated PET-MRI has been developed and implemented as a clinical scanner. 15 The MR-specific research area is relatively limited; however, interesting studies have been conducted, including pseudo-CT image synthesis from MR images for attenuation correction, 16 , 17 lung imaging with zero TE, 18 arterial spin labeling cross-validation, 19 and whole-body diffusion cross-validation with PET imaging. On the other hand, a PET detector insert combined with MRI transmit and receive coil system has been developed.…”