Michael N. Hoff

Toward Quantifying the Prevalence, Severity, and Cost Associated With Patient Motion During Clinical MR Examinations

PURPOSE To assess the prevalence, severity, and cost estimates associated with motion artifacts identified on clinical MR examinations, with a focus on the neuroaxis. METHODS A retrospective review of 1 randomly selected full calendar week of MR examinations (April 2014) was conducted for the detection of significant motion artifacts in examinations performed at a single institution on 3 different MR scanners. A base-case cost estimate was computed from recently available institutional data, and correlated with sequence time and severity of motion artifacts. RESULTS A total of 192 completed clinical examinations were reviewed. Significant motion artifacts were identified on sequences in 7.5% of outpatient and 29.4% of inpatient and/or emergency department MR examinations. The prevalence of repeat sequences was 19.8% of total MRI examinations. The base-case cost estimate yielded a potential cost to the hospital of

Combined geometric and algebraic solutions for removal of bSSFP banding artifacts with performance comparisons

592 per hour in lost revenue due to motion artifacts. Potential institutional average costs borne (revenue forgone) of approximately

SU‐E‐E‐01: ABR Diagnostic Radiology Core Exam: Was Our Redesigned Physics Course Successful in Teaching Physics to Radiology Residents?

115,000 per scanner per year may affect hospitals, owing to motion artifacts (univariate sensitivity analysis suggested a lower bound of

SU‐E‐I‐133: Novel Methods of Magnetic Resonance Imaging Near Metals

92,600, and an upper bound of

MRI sport-specific pulley imaging

139,000). CONCLUSIONS Motion artifacts represent a frequent cause of MR image degradation, particularly for inpatient and emergency department patients, resulting in substantial costs to the radiology department. Greater attention and resources should be directed toward providing practical solutions to this dilemma.

TU-H-206-05: Investigating the Resistance of GS-BSSFP to Motion Artifacts

Balanced steady state free precession (bSSFP) imaging suffers from off‐resonance artifacts such as signal modulation and banding. Solutions for removal of bSSFP off‐resonance dependence are described and compared, and an optimal solution is proposed.

Artifacts Affecting Musculoskeletal Magnetic Resonance Imaging: Their Origins and Solutions

PURPOSE Our purpose is to evaluate the effectiveness of our two year physics course in preparing radiology residents for the American Board of Radiology (ABR) diagnostic radiology exam. METHODS We designed a new two-year physics course that integrates radiology clinical content and practice and is primarily based on the AAPM curriculum and RSNA/AAPM physics modules. Biweekly classes focus on relevant concepts from assigned reading and use audience response systems to encourage participation. Teaching efficiency is optimized through lecturer rotations of physicists, radiologists, and guest speakers. An emphasis is placed on clinical relevance by requiring lab work and providing equipment demonstrations. Periodic quiz were given during the course. The course website was also redesigned for usability, and physics review lectures were conducted two weeks before the board exam to refresh key concepts. At the completion of our first two-year course, we conducted a confidential evaluation of the faculty and course. The evaluation assessed metrics such as overall organization, clinical relevance of content, and level of difficulty, with a rating scale from poor to excellent. RESULTS Our evaluation indicated that the redesigned course provided effective board exam preparation, with most responses between good and excellent. There was some criticism on the course length and on chronological discontinuity, but the review lectures were appreciated by the residents. All of our residents passed the physics component of the ABR exam with scores exceeding the minimum passing score by a significant margin. CONCLUSION The course evaluation and board exam results indicate that our new two-year course format provides valuable board exam preparation. This is possible thanks to the time and effort taken by the physics faculty on ensuring the residents get quality physics education.

MO-G-18C-01: BEST IN PHYSICS (IMAGING) - Novel Correction of Signal Modulation and Motion Artifacts in Temporal Bone BSSFP MRI

Purpose: This study demonstrates two novel MRI techniques for imaging near metals, and compares their artifact correction abilities, ease of use, acquisition time, and SNR. Future directions for imaging near metals are derived from this comparison. Methods: A water phantom containing an ASTM F75 Cobalt‐Chromium‐Molybdenum alloy hip prosthesis encased in a Lego structure was imaged using a 1.5T Siemens Avanto MRI scanner. For the 3D‐PLACE technique, two 3D turbo spin echo(TSE) complex datasets were acquired with 12×5mm slices, TR=300ms, TE=11ms, and variable frequency encoding gradients. Differing gradients allowed computation of a displacement field from the complex image phase difference for mapping pixels to their undistorted locations. Further post‐processing addressed fractional pixel shift. For the GS‐bSSFP technique, four 3D balanced steady state free precession (bSSFP) complex datasets were acquired with 52×3mm slices, flip angle=41 degrees, TR=4.2ms, TE=2.1ms, and phase cycling = 0, 90, 180, and 270 degrees respectively. For each pixel, the four phase cycled image values were plotted in the complex plane to locate the demodulated solution at the intersection of lines connecting alternating phase cycles. SNR was improved through a second pass solution. Comparisons were made through observations and parameter calculations. Results: Relative to 3D‐PLACE, GS‐bSSFP yielded ∼60% of the signal void, reduced signal pile‐up, and almost as accurate distortion correction. Strikingly, GS‐bSSFP achieved more than twice the SNR in 28% of the scan time of 3D‐PLACE, with no pulse sequence programming requirements. Conclusions: This study indicates that GS‐bSSFP shows potential for expeditious high signal clinical imaging near metals. Currently the technique is being revised to use less than four acquisitions; combined with limitations on the number of slices and subsampling techniques, this technique should become fast enough to be employed intraoperatively. Remnant distortion artifacts in GS‐SSFP images can be eliminated by combining the technique with 3D‐PLACE.

Practical CT Dose Monitoring: Current Tools and the Clinical Relevance

ObjectiveWe aim to create a novel MRI methodology that employs sport-specific stress views for imaging finger pulley injuries in the evaluation of post-operative healing effectiveness. The goal is to measure the bone to tendon distance (BTD), which is the current standard for determining pulley injuries.Materials and methodsThe athlete was imaged in a crimp-grip stressed position to emulate sport-specific biomechanics. A Gradient Echo technique was modified to maximize the signal to noise ratio and minimize distortion near the bone and tendon, simplifying the determination of the BTD.ResultsA stress-crimped hand position is imaged in less than one half-minute to enable diagnostic visualization of a normal proximal phalanx’ bone and tendon via measurement of their BTD.ConclusionThis novel stress methodology allows for sport-specific imaging, which is ideal for determining functional compromise of the hand’s pulley mechanism. Surgical outcomes may be more sensitively compared when using stress views, and these comparisons may then direct optimal repair technique. Future studies will utilize this technique to attempt early-stage detection of pulley injuries prior to complete rupture.

Avoiding MRI-Related Accidents: A Practical Approach to Implementing MR Safety

PURPOSE In addition to correcting magnetic field inhomogeneity-induced banding artifacts in balanced steady state free precession (bSSFP) MRI, preliminary in vivo studies indicate that the geometric solution (GS) also mitigates motion artifacts. The purpose here is to investigate the source of motion artifact correction through simulations, to further ascertain GS-bSSFPs clinical potential. METHODS Four bSSFP MR images with Δθ = 0°, 90°, 180°, and 270° respective phase cycling and TE/TR = 4.2/2.1ms were 1) acquired in vivo with a 3D axially-oriented sequence on a Philips Ingenia 3T MRI scanner using a flip angle α = 30°, and 180/180/120 matrix size and 1.0/1.0/1.0mm voxel size along frequency/phase/slice directions, and 2) simulated using α = 80°, parameters varied across the field-of-view (T1 relaxation = 200->3000ms, T2 relaxation = 40->3000ms, and field inhomogeneity θ = -π->+π), and added zero-mean Gaussian noise. The GS (the cross-point of lines/spokes connecting alternating phase cycles in the complex plane) and complex sum (CS) were computed pixel-by-pixel. Simulated data noise was reoriented in each associated spokes frame of reference in order to derive the noise radiality. Plots were then generated of GS and CS error and deviation as a function of the noise radiality in the original data. RESULTS In vivo data indicates that the GS mitigates motion artifacts relative to the CS in the foramen magnum region. Simulated data indicates that the GS has less error in size and deviation than the CS, and this discrepancy grows as noise radiality increases. CONCLUSION The GS shows more accuracy than the CS in all tests executed, especially as phasecycled image noise radiality increases. This implies that noise-like image artifacts such as those caused by motion and flow are suppressed by the GS, inspiring clinical applications of GS-bSSFP given its additional elimination of banding artifacts.