Impact of Education-based HEART Score Pathway on Coronary Computed Tomography Angiography Utilization and Yield in the Emergency Department.

OBJECTIVE: There is a growing consensus to reduce unnecessary testing among low-risk chest pain patients. The objective of this study was to evaluate the impact of implementing an education-based HEART score pathway in the emergency department on coronary computed tomography angiography (CCTA) utilization and yield. METHODS: A retrospective before and after intervention study was conducted at a single site. Adult emergency department patients undergoing CCTA for suspected acute coronary syndrome were included. Primary outcomes were CCTA utilization and yield. Utilization was defined as the percentage of patients evaluated with CCTA and yield was calculated as the percentage of patients with a diagnosis of obstructive coronary artery disease, defined as ≥50% stenosis in any one coronary artery due to atherosclerosis. RESULTS: 1540 patients undergoing CCTAs were included. CCTA utilization before and after were 2.2% [95% confidence interval (CI) 2.0-2.3] and 2.0% (95% CI 1.9-2.2), respectively; mean difference 0.1% (95% CI -0.1 to 0.3; P = 0.21). The mean age was 53 years (SD = 11) and females were 52%. Of 1477 patients included in CCTA yield analysis, patients diagnosed with obstructive coronary artery disease before and after were 15.0% (95% CI 12.6-17.7) and 16.2% (95% CI 13.6-19.1), respectively; mean difference 1.2% (95% CI -2.6 to 5.1; P = 0.53). CONCLUSIONS: There was no significant change in the CCTA utilization or yield after the implementation of an education-based HEART pathway in a large academic center. Our findings suggest adopting a more comprehensive approach for deploying such evidence-based protocols to increase institutional compliance.

Abnormal blood-brain barrier water exchange in chronic multiple sclerosis lesions: A preliminary study.

Relapsing-remitting multiple sclerosis (RRMS) is associated with persistent blood-brain barrier (BBB) dysfunction. The impact of this persistent dysfunction in both active and chronic MS lesions has yet to be investigated due to technological challenges associated with invasive assessment of BBB water transportation (e.g. 15O-PET). The purpose of this study was to test if persistent BBB dysfunction in RRMS manifests as lower BBB water exchange in chronic lesions using a recently developed noninvasive MRI paradigm. Patients with relapsing-remitting MS and healthy subjects were recruited for this prospective study. The novel Intrinsic Diffusivity Encoding of Arterial Labeled Spins (IDEALS) MRI method was used to map BBB water extraction fraction (Ew) and water permeability surface area product (PSw), as well as cerebral blood flow (CBF). Regional differences in BBB water exchange were evaluated between MS patients (normal appearing white matter [NAWM] and normal appearing gray matter [NAGM]) and healthy subjects (white matter [WM] and gray matter [GM]) and within MS subjects in non gadolinium-based contrast-agent (GBCA) enhancing chronic lesions, perilesional areas, and NAWM. Significantly lower PSw and Ew were observed in NAWM compared to WM (ΔPSw: -11.9 mL/100 g/min, p < .05; ΔEw: -4.3%, p < .01). Significantly lower Ew was observed in NAGM compared to GM (ΔEw: -12.1%, p < .01). Significantly lower PSw and CBF were observed in non-GBCA contrast enhancing lesions compared to NAWM (ΔPSw = -11.5 mL/100 g/min, p < .05; ΔCBF = -8.1 mL/100 g/min, p < .05). Ew was significantly higher in non-GBCA enhancing chronic MS lesions compared to NAWM (ΔEw = 1.6%, p < .05). The lower BBB water exchange in chronic MS lesions is consistent with previously reported observations and may demonstrate metabolic changes associated with MS.

In vivo evaluation of human patellar tendon microstructure and microcirculation with diffusion MRI.

BACKGROUND: Patellar tendon (PT) microstructure integrity and microcirculation status play a crucial role in the progression of tendinopathy and tendon repair. PURPOSE: To assess the feasibility and robustness of stimulated-echo based diffusion-weighted MRI with readout-segmented echo-planar imaging (ste-RS-EPI) for noninvasive assessment of microstructure and microcirculation of human PT. STUDY TYPE: Prospective. SUBJECTS: Fifteen healthy volunteers. FIELD STRENGTH/SEQUENCE: PT diffusion tensor imaging (DTI) and intravoxel incoherent motion (IVIM) were acquired with an ste-RS-EPI protocol on a 3T MRI scanner. ASSESSMENT: Subjects were positioned with their PT at the magic angle. DTI-derived parameters including axial diffusivity (AD), radial diffusivity (RD), mean diffusivity (MD), and fractional anisotropy (FA) were estimated with b-values of 0 and 800 s/mm2 and 12 diffusion directions. IVIM-derived parameters, f p , D* × f p , V b , and D* × V b were assessed in the central-third and the outer-two thirds of the PT with b-values of 0, 20, 30, 60, 80, 120, 200, 400, and 600 s/mm2 in three orthogonal directions. STATISTICAL TESTS: Paired t-tests were used to evaluate differences in IVIM parameters between the central-third and outer-two thirds regions of the patellar tendon. Paired t-tests and within-subject coefficient of variation were used to assess the intra- and intersession reproducibility of PT DTI and IVIM parameters. RESULTS: DTI parameters for healthy PT were 1.54 ± 0.09 × 10-3 mm2 /s, 1.01 ± 0.05 × 10-3 mm2 /s, 1.18 ± 0.06 × 10-3 mm2 /s, and 0.30 ± 0.04 for AD, RD, MD, and FA, respectively. Significantly higher (P < 0.05) IVIM parameters f p and D* × f p were observed in the outer-two thirds (6.1% ± 2.4% and 95.2 ± 49.6, respectively) compared with the central-third (3.8% ± 2.3% and 48.6 ± 35.2, respectively) of the PT. DATA CONCLUSION: Diffusion MRI of PT with an ste-RS-EPI protocol is clinically feasible. Both DTI- and IVIM-derived parameters of the PT demonstrated good test-retest reproducibility and interrater reliability. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:780-790.

Abbreviated quantitative UTE imaging in anterior cruciate ligament reconstruction.

BACKGROUND: Existing ultrashort echo time magnetic resonance imaging (UTE MRI) methods require prohibitively long acquisition times (~ 20-40 min) to quantitatively assess the clinically relevant fast decay T2* component in ligaments and tendons. The purpose of this study was to evaluate the feasibility and clinical translatability of a novel abbreviated quantitative UTE MRI paradigm for monitoring graft remodeling after anterior cruciate ligament (ACL) reconstruction. METHODS: Eight patients who had Graftlink™ hamstring autograft reconstruction were recruited for this prospective study. A 3D double-echo UTE sequence at 3.0 Tesla was performed at 3- and 6-months post-surgery. An abbreviated UTE MRI paradigm was established based on numerical simulations and in vivo validation from healthy knees. This proposed approach was used to assess the T2* for fast decay component ([Formula: see text]) and bound water signal fraction (fbw) of ACL graft in regions of interest drawn by a radiologist. RESULTS: Compared to the conventional bi-exponential model, the abbreviated UTE MRI paradigm achieved low relative estimation bias for [Formula: see text] and fbw over a range of clinically relevant values for ACL grafts. A decrease in [Formula: see text] of the intra-articular graft was observed in 7 of the 8 ACL reconstruction patients from 3- to 6-months (- 0.11 ± 0.16 ms, P = 0.10). Increases in [Formula: see text] and fbw from 3- to 6-months were observed in the tibial intra-bone graft ([Formula: see text]: 0.19 ± 0.18 ms, P < 0.05; Δfbw: 4% ± 4%, P < 0.05). Lower [Formula: see text] (- 0.09 ± 0.11 ms, P < 0.05) was observed at 3-months when comparing the intra-bone graft to the graft/bone interface in the femoral tunnel. The same comparisons at the 6-months also yielded relatively lower [Formula: see text] (- 0.09 ± 0.12 ms, P < 0.05). CONCLUSION: The proposed abbreviated 3D UTE MRI paradigm is capable of assessing the ACL graft remodeling process in a clinically translatable acquisition time. Longitudinal changes in [Formula: see text] and fbw of the ACL graft were observed.

Merging Orthovoltage X-Ray Minibeams spare the proximal tissues while producing a solid beam at the target.

Conventional radiation therapy of brain tumors often produces cognitive deficits, particularly in children. We investigated the potential efficacy of merging Orthovoltage X-ray Minibeams (OXM). It segments the beam into an array of parallel, thin (~0.3 mm), planar beams, called minibeams, which are known from synchrotron x-ray experiments to spare tissues. Furthermore, the slight divergence of the OXM array make the individual minibeams gradually broaden, thus merging with their neighbors at a given tissue depth to produce a solid beam. In this way the proximal tissues, including the cerebral cortex, can be spared. Here we present experimental results with radiochromic films to characterize the method's dosimetry. Furthermore, we present our Monte Carlo simulation results for physical absorbed dose, and a first-order biologic model to predict tissue tolerance. In particular, a 220-kVp orthovoltage beam provides a 5-fold sharper lateral penumbra than a 6-MV x-ray beam. The method can be implemented in arc-scan, which may include volumetric-modulated arc therapy (VMAT). Finally, OXM's low beam energy makes it ideal for tumor-dose enhancement with contrast agents such as iodine or gold nanoparticles, and its low cost, portability, and small room-shielding requirements make it ideal for use in the low-and-middle-income countries.

Pre-Clinical Translation of Second Harmonic Microscopy of Meniscal and Articular Cartilage Using a Prototype Nonlinear Microendoscope.

Previous studies using nonlinear microscopy have demonstrated that osteoarthritis (OA) is characterized by the gradual replacement of Type II collagen with Type I collagen. The objective of this study was to develop a prototype nonlinear laser scanning microendoscope capable of resolving the structural differences of collagen in various orthopaedically relevant cartilaginous surfaces. The current prototype developed a miniaturized femtosecond laser scanning instrument, mounted on an articulated positioning system, capable of both conventional arthroscopy and second-harmonic laser-scanning microscopy. Its optical system includes a multi-resolution optical system using a gradient index objective lens and a customized multi-purpose fiber optic sheath to maximize the collection of backscattered photons or provide joint capsule illumination. The stability and suitability of the prototype arthroscope to approach and image cartilage were evaluated through preliminary testing on fresh, minimally processed, and partially intact porcine knee joints. Image quality was sufficient to distinguish between hyaline cartilage and fibrocartilage through unique Type I and Type II collagen-specific characteristics. Imaging the meniscus revealed that the system was able to visualize differences in the collagen arrangement between the superficial and lamellar layers. Such detailed in vivo imaging of the cartilage surfaces could obviate the need to perform biopsies for ex vivo histological analysis in the future, and provide an alternative to conventional external imaging to characterize and diagnose progressive and degenerative cartilage diseases such as OA. Moreover, this system is readily customizable and may provide a suitable and modular platform for developing additional tools utilizing femtosecond lasers for tissue cutting within the familiar confines of two or three portal arthroscopy techniques.

MRI biomarkers in osseous tumors.

Although radiography continues to play a critical role in osseous tumor assessment, there have been remarkable advances in cross-sectional imaging. MRI has taken a lead in this assessment due to high tissue contrast and spatial resolution, which are well suited for bone lesion assessment. More recently, although somewhat lagging other organ systems, quantitative parameters have shown promising potential as biomarkers for osseous tumors. Among these sequences are chemical shift imaging (CSI), apparent diffusion coefficient (ADC), and intravoxel incoherent motion (IVIM) from diffusion-weighted imaging (DWI), quantitative dynamic contrast enhanced (DCE)-MRI, and magnetic resonance spectroscopy (MRS). In this article, we review the background and recent roles of these quantitative MRI biomarkers for osseous tumors. Level of Evidence: 3 Technical Efficacy Stage: 3 J. MAGN. RESON. IMAGING 2019. J. Magn. Reson. Imaging 2019;50:702-718.

3D MRI of whole-brain water permeability with intrinsic diffusivity encoding of arterial labeled spin (IDEALS).

This work proposes a novel MRI method - Intrinsic Diffusivity Encoding of Arterial Labeled Spin (IDEALS) - for the whole-brain mapping of water permeability in the human brain without an exogenous contrast agent. Quantitative separation of the intravascular and extravascular labeled water MRI signal was achieved in arterial spin labeling experiments with segmented 3D-GRASE acquisition by modulating the relative sensitivity between relaxation, true diffusion, and pseudodiffusion. The intrinsic diffusivity encoding in k-space created different broadening of the image-domain point spread functions for intravascular and extravascular labeled spins, from which blood-brain barrier (BBB) water extraction fraction (Ew) and water permeability surface area product (PSw) were estimated. The feasibility and sensitivity of this method was evaluated in healthy subjects at baseline and after caffeine challenge. The estimated baseline Ew and PSw maps showed contrast among gray matter (GM) and white matter (WM). GM Ew was significantly lower than that of WM (78.8% ±â€¯3.3% in GM vs. 83.9% ±â€¯4.6% in WM; p < 0.05) and GM PSw was significantly higher than that of WM (131.7 ±â€¯29.5 mL/100  g/min in GM vs. 76.2 ±â€¯18.4 mL/100  g/min in WM; p < 0.05). BBB Ew was significantly lower for females than males (74.9% ±â€¯3.7% for females vs. 81.3% ±â€¯3.3% for males in GM; 80.5% ±â€¯4.7% for females vs. 86.1 ±â€¯3.0 for males in WM; p < 0.05 for both), while significant PSw differences were only observed in WM (143.8 ±â€¯34.4 mL/100  g/min for females vs. 123.6 ±â€¯24.4 mL/100  g/min for males in GM; 91.6 ±â€¯15.0 mL/100  g/min for females vs. 65.9 ±â€¯12.5 mL/100  g/min for males in WM; p = 0.20 and p < 0.05 for GM and WM respectively). Significant correlations between Ew and CBF (r = -0.32, p < 0.05) and between PSw and CBF (r = 0.89, p < 0.05) were observed, consistent with 15O-H2O PET findings. After caffeine challenge, reduced CBF, Ew and PSw were observed, demonstrating the sensitivity of IDEALS approach.

Correlation of bone marrow cellularity and metabolic activity in healthy volunteers with simultaneous PET/MR imaging.

OBJECTIVE: To evaluate the correlation between bone marrow cellularity (BMC) and metabolic activity in healthy subjects and to see whether yellow marrow is indeed metabolically quiescent. Because metabolic activity can be assumed to reflect vascularity, we assessed the relationship between regional metabolic activity and geographic frequency of metastases as noted in the literature. MATERIALS AND METHODS: Two hundred and twenty locations (ten in each side of the pelvis and proximal femur) were evaluated in 11 consecutive healthy volunteers with simultaneous PET/MR. BMC was calculated through precise water-fat fraction quantification with a 6-echo gradient echo. We analyzed correlations between cellularity and SUVr, age, and R2*. We also looked at the relation between our results and the reported prevalence of metastases. RESULTS: There was moderate but statistically significant correlation between BMC and metabolic activity (r = 0.636, p < 0.0001). Interestingly, the iliac and sacrum had higher metabolic activity relative to cellularity, whereas the femoral neck and lesser trochanter showed lower SUVr than other regions with the similar cellularity. The relatively lower metabolic status of the femoral neck conflicted with its reported high frequency of metastasis. Excluding regions with almost no remaining red marrow, cellularity showed inverse relationship with age (r = 0.476, p < 0.0001) and direct relationship with R2* (r = 0.532, p < 0.0010). CONCLUSIONS: Metabolic activity of bone marrow was largely dependent on BMC while yellow marrow seems metabolically quiescent. The discrepancy between the assumed vascularity as determined by metabolic activity and reported sites of metastasis suggested that the process of bone metastasis may not depend entirely on vascularity.