Continuously moving table MRI with sliding multislice for rectal cancer staging: image quality and lesion detection

Continuously moving table MRI with golden angle radial sampling

PURPOSE

Continuously moving table (CMT) MRI is a high throughput technique that has multiple applications in whole-body imaging. In this work, CMT MRI based on golden angle (GA, 111.246° azimuthal step) radial sampling is developed at 3 Tesla (T), with the goal of increased flexibility in image reconstruction using arbitrary profile groupings.

THEORY AND METHODS

CMT MRI with GA and linear angle (LA) schemes were developed for whole-body imaging at 3T with a table speed of 20 mm/s. Imaging was performed in phantoms and a human volunteer with extended z fields of view of up to 1.8 meters. Four separate LA and a single GA scan were performed to enable slice reconstructions at four different thicknesses.

RESULTS

GA CMT MRI produced high image quality in phantoms and humans and allowed complete flexibility in reconstruction of slices with arbitrary slice thickness and position from a single data set. LA CMT MRI was constrained by predetermined parameters, required multiple scans and suffered from stair step artifacts that were not present in GA images.

CONCLUSION

GA sampling provides a robust flexible approach to CMT whole-body MRI with the ability to reconstruct slices at arbitrary positions and thicknesses from a single scan.

Temporally constrained respiratory gating improves continuously moving table MRI during free breathing

PURPOSE

To evaluate a novel breathing motion correction algorithm for continuously moving table magnetic resonance imaging (CMT-MRI) that optimizes motion consistency in a fixed time span.

MATERIALS AND METHODS

In 22 patients CMT-MRI was performed during free breathing. During a preparatory phase (constant) or continuously during the scan (adaptive) gating thresholds were computed from breathing states that should allow for motion consistent k-space sampling. After data from a first k-space traversal was acquired irrespective of breathing motion, subsequently k-space lines with discordant breathing states were reacquired below the gating threshold. Time constraints of CMT-MRI were respected, because a fixed time was allocated for reacquisition. Image quality and lesion depiction were evaluated on images reconstructed from the first traversal and motion-corrected images.

RESULTS

Compared to constant thresholds, gating with adaptive thresholds led to a higher number of reacquired k-space lines (60.1%/41.7%) and a larger fraction of motion consistent final k-space lines (96.6%/78.8%). Adaptive gating induced a significant increase in image quality for all regions affected by breathing motion. Only one of 22 lesions was not depicted on the adaptively corrected images, whereas 15 were readily appreciable.

CONCLUSION

Temporally constrained respiratory gating with adaptive thresholds allows for fully sampled, motion-corrected CMT-MRI acquisitions during free breathing.

Peripheral vessel scout imaging based on continuously moving table acquisition of projection data

A fast and spatially seamless peripheral vessel scout is desirable for subsequent planning of magnetic resonance (MR) angiography. We implemented a continuously moving table sequence providing projection data with time-of-flight contrast of the entire lower extremities in less than 2 minutes. Variation of arterial signal during the cardiac cycle and autocorrelation were exploited to enhance vessel-to-background contrast. Subjective image analysis revealed excellent vessel depiction, indicating that the proposed scout allows for seamless expedited visualization of major arterial structures.

Comparison of a new whole-body continuous-table-movement protocol versus a standard whole-body MR protocol for the assessment of multiple myeloma

OBJECTIVES

To evaluate a whole body (WB) continuous-table-movement (CTM) MR protocol for the assessment of multiple myeloma (MM) in comparison to a step-by-step WB protocol.

METHODS

Eighteen patients with MM were examined at 1.5T using a WB CTM protocol (axial T2-w fs BLADE, T1-w GRE sequence) and a step-by-step WB protocol including coronal/sagittal T1-w SE and STIR sequences as reference. Protocol time was assessed. Image quality, artefacts, liver/spleen assessability, and the ability to depict bone marrow lesions less than or greater than 1 cm as well as diffuse infiltration and soft tissue lesions were rated. Potential changes in the Durie and Salmon Plus stage and the detectability of complications were assessed.

RESULTS

Mean protocol time was 6:38 min (CTM) compared to 24:32 min (standard). Image quality was comparable. Artefacts were more prominent using the CTM protocol (P = 0.0039). Organ assessability was better using the CTM protocol (P < 0.001). Depiction of bone marrow and soft tissue lesions was identical without a staging shift. Vertebral fractures were not detected using the CTM protocol.

CONCLUSIONS

The new protocol allows a higher patient throughput and facilitates the depiction of extramedullary lesions. However, as long as vertebral fractures are not detectable, the protocol cannot be safely used for clinical routine without the acquisition of an additional sagittal sequence.