Reduction of procedure times in routine clinical practice with Compressed SENSE magnetic resonance imaging technique

Abstract

Objectives: Acceleration of MR sequences beyond current parallel imaging techniques is possible with the Compressed SENSE technique that has recently become available for 1.5 and 3 Tesla scanners, for nearly all image contrasts and for 2D and 3D sequences. The impact of this technique on examination timing parameters and MR protocols in a clinical setting was investigated in this retrospective study.

Material and methods: A numerical analysis of the examination timing parameters (scan time, exam time, procedure time, interscan delay time, changeover time, nonscan time) based on the MR protocols of 6 different body regions (brain, knee, lumbar spine, breast, shoulder) using MR log files was performed and the total number of examinations acquired from January to April both in 2017 and 2018 on a 1.5 T MR scanner was registered. Percentages, box plots and unpaired two-sided t tests were obtained for statistical evaluation.

Results: All examination timing parameters of the six anatomical regions analysed were significantly shortened after implementation of Compressed SENSE. On average, scan times were accelerated by 20.2% (p<0.0001) while procedure times were shortened by 16% (p<0.0001). Considering all anatomical regions and all MR protocols, 27% more examinations were performed over the same 4 month period in 2018 compared to 2017.

Conclusion: Compressed SENSE allows for a significant acceleration of MR examinations and a considerable increase in the total number of MR examinations is possible.

Fig 1. Graphical representation of examination timing parameters in a single patient.

Procedure time is the duration the patient is in the scanner room, exam time is the sum of actual scan time (data acquisition) and inter scan delays such as planning of imaging stacks, communication with the patient and admission of contrast agent. The changeover time is the time required to put the patient on and off the table. Scan time is equivalent to the periods that the scanner is acquiring data (dashed blocks), while non-scan time is defined as all period where the scanner is not acquiring data (blank blocks).

Fig 2. MR scanning parameters, times of individual sequences and the total exam prior to and after introduction of Compressed SENSE.

FOV, resolution and most important scan parameters (TE / TR / flip angle) of the exams and the timings of the individual sequences and the total exam as performed prior to and after the introduction of Compressed SENSE are mentioned. The Compressed SENSE reduction factors are described where applicable. The total acceleration factor of a single sequence as well as of the full exam are given. Note that for brain, breast and shoulder Compressed SENSE was used for acceleration only, while in case of knee, lumbar spine and wrist a hybrid approach was chosen; in some sequences Compressed SENSE was used for acceleration, while other 2D scans were replaced by a (near-)isotropic 3D sequence with a similar weighting. “N.A.” means “not available” and is used if this sequence was not acquired after optimization of MR protocol with the Compressed SENSE technique. “No” means, that this sequence was acquired without Compressed SENSE technique in the original and the modified MR protocol.

Fig 3. Illustration of image contrast achieved without and with Compressed SENSE in brain on 3D T1 m-Dixon TFE post-contrast images.

Transverse image reconstructions of a sagittally scanned 3D T1 m-Dixon TFE postcontrast sequence acquired without (A and C) and with Compressed SENSE (B and D). A Compressed SENSE reduction factor of 7 was chosen. The image impression is comparable with and without Compressed SENSE.

Fig 4. Illustration of image contrast achieved without and with Compressed SENSE in brain on 3D FLAIR images.

Transverse image reconstructions of a sagittally scanned 3D FLAIR sequence acquired without (A and C) and with Compressed SENSE (B and D). A Compressed SENSE reduction factor of 7.8 was chosen. Comparable image impression with and without Compressed SENSE.

Fig 5. 3D T2 spine view in lumbar spine.

Sagittally scanned high resolution 3D T2 spine view of the lumbar spine acquired with nearly isotropic voxels and Compressed SENSE in a patient with spinal canal stenosis (A). Secondary multiplanar transverse (B and C) and coronal reconstructions (D) were performed.

Fig 6. The mix of MR procedures.

The mix of MR procedures before implementation of Compressed SENSE from January to April 2017 as well as after implementation of Compressed SENSE from January to April 2018. All MR examinations based on standard and non-standard protocols in all anatomical regions were included.

Fig 7. Exam timing parameters derived from the MR log files.

All exam timing parameters are depicted in minutes for the 6 selected anatomical regions (brain, knee, lumbar spine, breast, wrist and shoulder (Fig. 7a). Only the standard protocol of each anatomical region was considered. The same data is depicted in boxplots (Fig 7b).

Fig 8. The average exam timing parameters.

The average exam timing parameters for the 6 selected anatomical regions as derived from the log files, depicted in numbers and in bar plots. All MR examinations based on standard and non-standard protocols of the respective anatomical region were considered.

Fig 9. The total number of MR examinations.

The total number of MR examinations obtained in the selected 4 month time period. All MR examinations based on standard and non-standard protocols in all anatomical regions were included.