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1. Assessment of uterine artery geometry and hemodynamics in human pregnancy with 4d flow mri and its correlation with doppler ultrasound

   https://doi.org/10.1002/jmri.26229  

   Hwuang, Eileen ; Vidorreta, Marta ; Schwartz, Nadav ; Moon, Brianna F. ; Kochar, Kirpal ; Tisdall, Matthew Dylan ; Detre, John A. ; Witschey, Walter R. T. ( November 2018 , Journal of Magnetic Resonance Imaging)

   Uterine artery (UtA) hemodynamics might be used to predict risk of hypertensive pregnancy disorders, including preeclampsia and intrauterine growth restriction.

   To determine the feasibility of 4D flow MRI in pregnant subjects by characterizing UtA anatomy, computing UtA flow, and comparing UtA velocity, and pulsatility and resistivity indices (PI, RI) with transabdominal Doppler ultrasound (US).

   Prospective cross‐sectional study from June 6, 2016, to May 2, 2018.

   Forty‐one singleton pregnant subjects (age [range] = 27.0 ± 5.9 [18–41] years) in their second or third trimester. We additionally scanned three subjects who had prepregnancy diabetes or chronic hypertension.

   The subjects underwent UtA and placenta MRI using noncontrast angiography and 4D flow at 1.5T.

   UtA anatomy was described based on 4D flow‐derived noncontrast angiography, while UtA flow properties were characterized by net flow, systolic/mean/diastolic velocity, PI and RI through examination of 4D flow data. PI and RI are standard hemodynamic parameters routinely reported on Doppler US.

   Spearman's rank correlation, Wilcoxon signed rank tests, and Bland‐Altman plots were used to preliminarily investigate the relationships between flow parameters, gestational age, and Doppler US. or

   4D flow MRI and UtA flow quantification was feasible in all subjects. There was considerable heterogeneity in UtA geometry in each subject between left and right UtAs and between subjects. Mean 4D flow‐based parameters were: mean bilateral flow rate = 605.6 ± 220.5 mL/min, PI = 0.72 ± 0.2, and RI = 0.47 ± 0.1. Bilateral flow did not change with gestational age. We found that MRI differed from US in terms of lower PI (mean difference ‐0.1) and RI (mean difference < ‐0.1) with Wilcoxon signed rank testP = 0.05 andP = 0.13, respectively.

   4D flow MRI is a feasible approach for describing UtA anatomy and flow in pregnant subjects.

   Level of Evidence:

   Technical Efficacy:Stage 1

   J. Magn. Reson. Imaging 2019;49:59–68.

    

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2. Addressing CT metal artifacts using photon‐counting detectors and one‐step spectral CT image reconstruction

   https://doi.org/10.1002/mp.15621  

   Schmidt, Taly Gilat ; Sammut, Barbara A. ; Barber, Rina Foygel ; Pan, Xiaochuan ; Sidky, Emil Y. ( April 2022 , Medical Physics)

   The constrained one‐step spectral CT image reconstruction (cOSSCIR) algorithm with a nonconvex alternating direction method of multipliers optimizer is proposed for addressing computed tomography (CT) metal artifacts caused by beam hardening, noise, and photon starvation. The quantitative performance of cOSSCIR is investigated through a series of photon‐counting CT simulations.

   cOSSCIR directly estimates basis material maps from photon‐counting data using a physics‐based forward model that accounts for beam hardening. The cOSSCIR optimization framework places constraints on the basis maps, which we hypothesize will stabilize the decomposition and reduce streaks caused by noise and photon starvation. Another advantage of cOSSCIR is that the spectral data need not be registered, so that a ray can be used even if some energy window measurements are unavailable. Photon‐counting CT acquisitions of a virtual pelvic phantom with low‐contrast soft tissue texture and bilateral hip prostheses were simulated. Bone and water basis maps were estimated using the cOSSCIR algorithm and combined to form a virtual monoenergetic image for the evaluation of metal artifacts. The cOSSCIR images were compared to a “two‐step” decomposition approach that first estimated basis sinograms using a maximum likelihood algorithm and then reconstructed basis maps using an iterative total variation constrained least‐squares optimization (MLE+TV). Images were also compared to a nonspectral TV reconstruction of the total number of counts detected for each ray with and without normalized metal artifact reduction (NMAR) applied. The simulated metal density was increased to investigate the effects of increasing photon starvation. The quantitative error and standard deviation in regions of the phantom were compared across the investigated algorithms. The ability of cOSSCIR to reproduce the soft‐tissue texture, while reducing metal artifacts, was quantitatively evaluated.

   Noiseless simulations demonstrated the convergence of the cOSSCIR and MLE+TV algorithms to the correct basis maps in the presence of beam‐hardening effects. When noise was simulated, cOSSCIR demonstrated a quantitative error of −1 HU, compared to 2 HU error for the MLE+TV algorithm and −154 HU error for the nonspectral TV+NMAR algorithm. For the cOSSCIR algorithm, the standard deviation in the central iodine region of interest was 20 HU, compared to 299 HU for the MLE+TV algorithm, 41 HU for the MLE+TV+Mask algorithm that excluded rays through metal, and 55 HU for the nonspectral TV+NMAR algorithm. Increasing levels of photon starvation did not impact the bias or standard deviation of the cOSSCIR images. cOSSCIR was able to reproduce the soft‐tissue texture when an appropriate regularization constraint value was selected.

   By directly inverting photon‐counting CT data into basis maps using an accurate physics‐based forward model and a constrained optimization algorithm, cOSSCIR avoids metal artifacts due to beam hardening, noise, and photon starvation. The cOSSCIR algorithm demonstrated improved stability and accuracy compared to a two‐step method of decomposition followed by reconstruction.

    

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3. Usability and Performance Evaluation of a Novel Surgical Suture Needle in a Cadaveric Tendon Model

   Diaz, Miguel A. ; Branch, Eric A. ; Dunn, Jake ; Brothers, Anthony ; Jordan, Steve ( February 2023 , Transactions of the annual meeting of the Orthopaedic Research Society)

   INTRODUCTION: In practice, the use of a whip stitch versus a locking stitch in anterior cruciate ligament (ACL) graft preparation is based on surgeon preference. Those who prefer efficiency and shorter stitch time typically choose a whip stitch, while those who require improved biomechanical properties select a locking stitch, the gold standard of which is the Krackow method. The purpose of this study was to evaluate a novel suture needle design that can be used to perform two commonly used stitch methods, a whip stitch, and a locking stitch, by comparing the speed of graft preparation and biomechanical properties. It was hypothesized that adding a locking mechanism to the whip stitch would improve biomechanical performance but would also require more time to complete due to additional steps required for the locking technique. METHODS: Graft preparation was performed by four orthopaedic surgeons of different training levels where User 1 and User 2 were both attendings and User’s 3 and 4 were both fellows. A total of 24 matched pair cadaveric knees were dissected and a total of 48 semitendinosus tendons were harvested. All grafts were standardized to the same size. Tendons were randomly divided into 4 groups (12 tendons per group) such that each User performed analogous stitch on matched pair: Group 1, User 1 and User 3 performed whip stitches; Group 2, User 1 and User 3 performed locking stitches; Group 3, User 2 and User 4 performed whip stitches; Group 4, User 2 and User 4 performed locking stitches. For instrumentation, the two ends of tendon grafts were clamped to a preparation stand. A skin marker was used to mark five evenly spaced points, 0.5 cm apart, as a guide to create a 5-stitch series. The stitches were performed with EasyWhip, a novel two-part suture needle which allows one to do both a traditional whip stitch and a locking whip stitch, referred to as WhipLock (Figure 1). The speed for graft preparation was timed for each User. Biomechanical testing was performed using a servohydraulic testing machine (MTS Bionix) equipped with a 5kN load cell (Figure 2). A standardized length of tendon, 10 cm, was coupled to the MTS actuator by passing it through a cryoclamp cooled by dry ice to a temperature of -5°C. All testing samples were pre-conditioned to normalize viscoelastic effects and testing variability through application of cyclical loading to 25-100 N for three cycles. The samples were then held at 89 N for 15 minutes. Thereafter, the samples were loaded to 50-200 N for 500 cycles at 1 Hz. If samples survived, they were ramped to failure at 20 mm/min. Displacement and force data was collected throughout testing. Metrics of interest were peak-to-peak displacement (mm), stiffness (N/mm), ultimate failure load (N) and failure mode. Data are presented as averages and standard deviations. A Wilcoxon signed-rank test was used to evaluate the groups for time to complete stitch and biomechanical performance. Statistical significance was set at P = .05. RESULTS SECTION: In Group 1, the time to complete the whip stitch was not significantly different between User 1 and User 3, where the average completion time was 1 min 13 sec. Similarly, there were no differences between Users when performing the WhipLock (Group 2) with an average time of 1 min 49 sec. In Group 3 (whip stitch), User 2 took 1 min 48 sec to complete the whip stitch, whereas User 4 took 1 min 25 sec (p=.033). The time to complete the WhipLock stitch (Group 4) was significantly different, where User 2 took 3 min and 44 sec, while User 4 only took 2 min 3 sec (p=.002). Overall, the whip stitch took on average 1 min 25 sec whereas the WhipLock took 2 min 20 sec (p=.001). For whip stitch constructs, no differences were found between Users and all stitches were biomechanically equivalent. Correspondingly, for WhipLock stitches, no differences were found between Users and all suture constructs were likewise biomechanically equivalent. Averages for peak-to-peak displacement (mm), stiffness (N/mm), and ultimate failure load (N) are presented in Table 1. Moreover, when the two stitch methods were compared, the WhipLock constructs significantly increased stiffness by 25% (p <.001), increased ultimate failure load by 35% (p<.001) and reduced peak-to-peak displacement by 55% (p=.001). The common mode of failure for grafts with whip stitch failed by suture pullout from tendon (18/24), where a few instances occurred by suture breakage (6/24). Tendon grafts with WhipLock stitch commonly failed by suture breakage (22/24), where two instances of combined tendon tear and suture breakage were noted. DISCUSSION: The WhipLock stitch significantly increased average construct stiffness and ultimate failure load, while significantly reducing the peak-to- peak displacement compared to the whip stitch. These added strength benefits of the WhipLock stitch took 55 seconds more to complete than the whip stitch. No statistically significant difference in biomechanical performance was found between the Users. Data suggests equivalent stitch performance regardless of the time to complete stitch and surgeon training level. SIGNIFICANCE/CLINICAL RELEVANCE: Clinically, having a suture needle device available which can be used to easily perform different constructs including one with significant strength advantages regardless of level of experience is of benefit. 

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4. MR method for measuring microscopic histologic soft tissue textures

   https://doi.org/10.1002/mrm.28731  

   Sonn, Geoffrey A. ; Fan, Richard E. ; Kunder, Christian A. ; Gold, Garry E. ; James, Kristin M. ; Parker, Ian D. ; Carlson, Jean M. ; Cannizzaro, Scott M. ; James, Timothy W. ( February 2021 , Magnetic Resonance in Medicine)

   Provide a direct, non‐invasive diagnostic measure of microscopic tissue texture in the size scale between tens of microns and the much larger scale measurable by clinical imaging. This paper presents a method and data demonstrating the ability to measure these microscopic pathologic tissue textures (histology) in the presence of subject motion in an MR scanner. This size range is vital to diagnosing a wide range of diseases.

   MR micro‐Texture (MRµT) resolves these textures by a combination of measuring a targeted set of k‐values to characterize texture—as in diffraction analysis of materials, performing a selective internal excitation to isolate a volume of interest (VOI), applying a high k‐value phase encode to the excited spins in the VOI, and acquiring each individual k‐value data point in a single excitation—providing motion immunity and extended acquisition time for maximizing signal‐to‐noise ratio. Additional k‐value measurements from the same tissue can be made to characterize the tissue texture in the VOI—there is no need for these additional measurements to be spatially coherent as there is no image to be reconstructed. This method was applied to phantoms and tissue specimens including human prostate tissue.

   Data demonstrating resolution <50 µm, motion immunity, and clearly differentiating between normal and cancerous tissue textures are presented.

   The data reveal textural differences not resolvable by standard MR imaging. As MRµT is a pulse sequence, it is directly translatable to MRI scanners currently in clinical practice to meet the need for further improvement in cancer imaging.

    

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5. Fast chemical exchange saturation transfer imaging based on PROPELLER acquisition and deep neural network reconstruction

   https://doi.org/10.1002/mrm.28376  

   Guo, Chenlu ; Wu, Jian ; Rosenberg, Jens T. ; Roussel, Tangi ; Cai, Shuhui ; Cai, Congbo ( June 2020 , Magnetic Resonance in Medicine)

   To develop a method for fast chemical exchange saturation transfer (CEST) imaging.

   The periodically rotated overlapping parallel lines enhanced reconstruction (PROPELLER) sampling scheme was introduced to shorten the acquisition time. Deep neural network was employed to reconstruct CEST contrast images. Numerical simulation and experiments on a creatine phantom, hen egg, and in vivo tumor rat brain were performed to test the feasibility of this method.

   The results from numerical simulation and experiments show that there is no significant difference between reference images and CEST‐PROPELLER reconstructed images under an acceleration factor of 8.

   Although the deep neural network is trained entirely on synthesized data, it works well on reconstructing experimental data. The proof of concept study demonstrates that the combination of the PROPELLER sampling scheme and the deep neural network enables considerable acceleration of saturated image acquisition and may find applications in CEST MRI.

    

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