Ultrafast volumetric B1 (+) mapping for improved radiofrequency shimming in 3 tesla body MRI.
← Research streamUsing multi-slice adaptive RF shimming (MS-RF shim) based on volumetric DREAM B1+ calibration scans, mean deviation from nominal flip angle was reduced to less than 11% across slices/targets/subjects. Relative improvements in B1+ homogeneity (cv) for MS-RF sh…
Study snapshot
Abstract
PURPOSE: To evaluate the use of the recently proposed ultrafast B1 (+) mapping approach DREAM (Dual Refocusing Echo Acquisition Mode) for a refinement of patient adaptive radiofrequency (RF) shimming. MATERIALS AND METHODS: Volumetric DREAM B1 (+) calibration scans centered in the upper abdomen were acquired in 20 patients and three volunteers with written informed consent at a clinical dual source 3 Tesla (T) MR system. Based on these data, RF transmit settings were optimized by central-slice based RF-shimming (CS-RF shim) and by a refined, multi-slice adaptive approach (MS-RF shim). Simulations were performed to compare flip angle accuracy and B1 (+) homogeneity (cv = stddev/mean) achieved by CS-RF shim versus MS-RF shim for transversal and coronal slices, and for volume shimming on the spine. RESULTS: By MS-RF shim, mean deviation from nominal flip angle was reduced to less than 11% in all slices, all targets, and all subjects. Relative improvements in B1 (+) cv (MS-RF shim versus CS-RF) were up to 14%/39%/47% in transversal slices/coronal slices/ spine area. CONCLUSION: Volumetric information about B1 (+) can be used to further improve the accuracy and homogeneity of the B1 (+) field yielding higher diagnostic confidence, and will also be of value for various quantitative methods which are sensitive to flip angle imperfections.
AI evidence extraction
Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.
Main findings
Using multi-slice adaptive RF shimming (MS-RF shim) based on volumetric DREAM B1+ calibration scans, mean deviation from nominal flip angle was reduced to less than 11% across slices/targets/subjects. Relative improvements in B1+ homogeneity (cv) for MS-RF shim versus central-slice RF shimming were reported up to 14% (transversal), 39% (coronal), and 47% (spine area).
Outcomes measured
- B1+ mapping performance (DREAM)
- Flip angle accuracy (deviation from nominal)
- B1+ homogeneity (coefficient of variation, cv)
- Performance of RF shimming approaches (CS-RF shim vs MS-RF shim)
View raw extracted JSON
{
"study_type": "engineering",
"exposure": {
"band": "RF",
"source": "MRI",
"frequency_mhz": null,
"sar_wkg": null,
"duration": null
},
"population": "20 patients and three volunteers",
"sample_size": 23,
"outcomes": [
"B1+ mapping performance (DREAM)",
"Flip angle accuracy (deviation from nominal)",
"B1+ homogeneity (coefficient of variation, cv)",
"Performance of RF shimming approaches (CS-RF shim vs MS-RF shim)"
],
"main_findings": "Using multi-slice adaptive RF shimming (MS-RF shim) based on volumetric DREAM B1+ calibration scans, mean deviation from nominal flip angle was reduced to less than 11% across slices/targets/subjects. Relative improvements in B1+ homogeneity (cv) for MS-RF shim versus central-slice RF shimming were reported up to 14% (transversal), 39% (coronal), and 47% (spine area).",
"effect_direction": "benefit",
"limitations": [],
"evidence_strength": "low",
"confidence": 0.74,
"peer_reviewed_likely": "yes",
"keywords": [
"B1+ mapping",
"DREAM",
"Dual Refocusing Echo Acquisition Mode",
"radiofrequency shimming",
"RF transmit settings",
"3 Tesla",
"body MRI",
"flip angle",
"B1+ homogeneity",
"upper abdomen"
],
"suggested_hubs": [
{
"slug": "mri-rf",
"weight": 0.9,
"reason": "Study evaluates RF (B1+) mapping and RF shimming methods in a 3T clinical MRI system."
}
]
}AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.
Identifiers and source
DOI: 10.1002/jmri.24438
PubMed: 24924914