Increase In Imaging Time Research Articles

Feasibility study of computed high b-value diffusion-weighted magnetic resonance imaging for pediatric posterior fossa tumors.

To evaluate the diagnostic efficacy of computed diffusion-weighted imaging (DWI) in pediatric posterior fossa tumors generated using high b-values. We retrospectively performed our study on 32 pediatric patients who had undergone brain magnetic resonance imaging for a posterior fossa tumor between January 2016 and January 2022. The DWIs were evaluated for each patient by two blinded radiologists. The computed DWI (cDWI) was mathematically derived using a mono-exponential model from images with b = 0 and 1,000 s/mm2 and high b-values of 1,500, 2,000, 3,000, and 5,000 s/mm2. The posterior fossa tumors were divided into two groups, low grade and high grade, and the tumor/thalamus signal intensity (SI) ratios were compared. The Mann-Whitney U test and receiver operating characteristic (ROC) curves were used to compare the diagnostic performance of the acquired DWI (DWI1000), apparent diffusion coefficient (ADC)1000 maps, and cDWI (cDWI1500, cDWI2000, cDWI3000, and cDWI5000). The comparison of the two tumor groups revealed that the tumor/thalamus SI ratio on the DWI1000 and cDWI (cDWI1500, cDWI2000, cDWI3000, and cDWI5000) was statistically significantly higher in high-grade tumors (P < 0.001). In the ROC curve analysis, higher sensitivity and specificity were detected in the cDWI1500, cDWI2000, cDWI3000, and ADC1000 maps (100%, 90.90%) compared with the DWI1000 (80%, 81.80%). cDWI3000 had the highest area under the curve (AUC) value compared with other parameters (AUC: 0.976). cDWI generated using high b-values was successful in differentiating between low-grade and high-grade posterior fossa tumors without increasing imaging time. cDWI created using high b-values can provide additional information about tumor grade in pediatric posterior fossa tumors without requiring additional imaging time.

Effectiveness of Brachial Plexus Blocks in Obesity: Secondary Analysis of Randomized Controlled Trial.

Brachial plexus block for hand and upper extremity procedures in the obese presents a unique set of technical challenges. The authors examined how obesity affects procedural success, quality of anesthesia, and patient satisfaction. Secondary analysis of a randomized control trial comparing the retroclavicular versus supraclavicular brachial plexus block for distal upper extremity surgery was conducted. Patients were randomized to supraclavicular or retroclavicular brachial plexus block groups in the original trial. In this study, the authors dichotomized patients by obesity to compare differences in outcomes. Sixteen of 117 patients (13.7%) were obese. The groups were statistically well balanced in terms of baseline and operative variables. Obese patients had increased imaging time 2.7 minutes (95% confidence interval [CI], 1.44-3.92) versus 1.9 minutes (95% CI, 1.64-2.16), P value = .05; needling time 6.6 minutes (95% CI, 5.17-7.95) versus 5.8 minutes (95% CI, 5.04-5.74), P = .02; and procedure time 9.3 minutes (95% CI, 7.04-11.46) versus 7.3 minutes (95% CI, 6.79-7.79), P = .01. Block success and complications were not statistically significant. The visual analog scores during the block, at 2 hours, and 24 hours after were not statistically different. Patient satisfaction score among obese patients was 9.1 (95% CI, 8.6-9.6) versus 9.2 (95% CI, 9.1-9.4), P = .63. Findings from this trial suggest that despite an increased procedural difficulty, the use of both supraclavicular and retroclavicular brachial plexus blocks is associated with comparable quality of anesthesia, similar complication profile, equal opioid requirements, and similar patient satisfaction in the obese.

Optimized sinusoidal patterns for high-performance computational ghost imaging.

Computational ghost imaging (CGI) can reconstruct scene images by two-order correlation between sampling patterns and detected intensities from a bucket detector. By increasing the sampling rates (SRs), imaging quality of CGI can be improved, but it will result in an increasing imaging time. Herein, in order to achieve high-quality CGI under an insufficient SR, we propose two types of novel sampling methods for CGI, to the best of our knowledge, cyclic sinusoidal-pattern-based CGI (CSP-CGI) and half-cyclic sinusoidal-pattern-based CGI (HCSP-CGI), in which CSP-CGI is realized by optimizing the ordered sinusoidal patterns through "cyclic sampling patterns," and HCSP-CGI just uses half of the sinusoidal pattern types of CSP-CGI. Target information mainly exists in the low-frequency region, and high-quality target scenes can be recovered even at an extreme SR of 5%. The proposed methods can significantly reduce the sampling number and real-time ghost imaging possible. The experiments demonstrate the superiority of our method over state-of-the-art methods both qualitatively and quantitatively.

NIR-II fluorescence lymphatic imaging and intraoperative navigation based on the “isolated cage” monodisperse strategy

Fluorescence imaging in the second near-infrared (NIR-II) window is well suited for biological systems due to lower tissue scattering and micrometer-scale resolution at depths of millimeters. Unfortunately, none of the NIR-II fluorophores have clinical application due to low quantum yields, poor photostability, and long-term biosafety concerns. Herein, we develop NIR-II fluorescent nanoprobes based on the "isolated cage" monodisperse strategy, which significantly inhibits the π-π stacking interactions and restricts internal rotation of the arrested indocyanine green (ICG) fluorophores, which minimizes aggregation-caused quenching and enhances their NIR-II imaging performance. Unlike ICG's imaging window of several minutes, the nanoformulations have reduced photobleaching and provide longer observation times. The increased imaging time allows high spatiotemporal resolution of blood vessels and lymphatic system. Benefiting from the high resolution and sensitivity of the nanoprobes, sentinel lymph nodes are accurately removed under fluorescence navigation. More intriguingly, the patency of lymphovenous anastomosis (LVA) is presented more intuitively by qualitative and quantitative NIR-II fluorescence signals, which will directly benefit the innovation and promotion of LVA.

Deep learning reconstruction for 1.5 T cervical spine MRI: effect on interobserver agreement in the evaluation of degenerative changes.

To investigate whether deep learning reconstruction (DLR) provides improved cervical spine MR images using a 1.5 T unit in the evaluation of degenerative changes without increasing imaging time. This study included 21 volunteers (age 42.4 ± 11.9 years; 17 males) who underwent 1.5 T cervical spine sagittal T2-weighted MRI. From the imaging data with number of acquisitions (NAQ) of 1 or 2, images were reconstructed with DLR (NAQ1-DLR) and without DLR (NAQ1) or without DLR (NAQ2), respectively. Two readers evaluated the images for depiction of structures, artifacts, noise, overall image quality, spinal canal stenosis, and neuroforaminal stenosis. The two readers read studies blinded and randomly. Values were compared between NAQ1-DLR and NAQ1 and between NAQ1-DLR and NAQ2 using the Wilcoxon signed-rank test. The analyses showed significantly better results for NAQ1-DLR compared with NAQ1 and NAQ2 (p < 0.023), except for depiction of disc and foramina by one reader and artifacts by both readers in the comparison between NAQ1-DLR and NAQ2. Interobserver agreements (Cohen's weighted kappa [97.5% confidence interval]) in the evaluation of spinal canal stenosis for NAQ1-DLR/NAQ1/NAQ2 were 0.874 (0.866-0.883)/0.778 (0.767-0.789)/0.818 (0.809-0.827), respectively, and those in the evaluation of neuroforaminal stenosis were 0.878 (0.872-0.883)/0.855 (0.849-0.860)/0.852 (0.845-0.860), respectively. DLR improved the 1.5 T cervical spine MR images in the evaluation of degenerative spine changes. • Two radiologists demonstrated that deep learning reconstruction reduced the noise in cervical spine sagittal T2-weighted MR images obtained using a 1.5 T unit. • Reduced noise in deep learning reconstruction images resulted in a clearer depiction of structures, such as the spinal cord, vertebrae, and zygapophyseal joint. • Interobserver agreement in the evaluation of spinal canal stenosis and foraminal stenosis on cervical spine MR images was significantly improved using deep learning reconstruction (0.874 and 0.878, respectively) versus without deep learning (0.778-0.818 and 0.852-0.855, respectively).

Brain MR image super-resolution via a deep convolutional neural network with multi-unit upsampling learning

Image super-resolution (SR) is a preferred approach to achieving high-resolution MR images because they are typically achieved in real world at the expense of reduced signal-to-noise ratio and/or increased imaging time. A novel deep residual network (DRN) with multi-unit upsampling learning is designed for MR image SR. The multi-unit upsampling learning mechanism involves multi-unit upsampling and adaptive learning. The designed DRN performs the SR task in the LR space to accelerate the network via an upsampling strategy at the late stage of the network architecture. A multi-unit upsampling strategy is proposed to transmit lost information in each residual unit and to accumulate the upscaled feature maps achieved by different residual units. An adaptive learning strategy following multi-unit upsampling is utilized to potentially discover the contributions of these upscaled feature maps to high-resolution MR image reconstruction by adaptively assigning different significance weights to the intermediate predictions. The proposed DRN achieves a fair good reconstruction performance, which is superior to some state-of-the-art deep-learning-based methods.

MRI Super-Resolution Through Generative Degradation Learning.

Spatial resolution plays a critically important role in MRI for the precise delineation of the imaged tissues. Unfortunately, acquisitions with high spatial resolution require increased imaging time, which increases the potential of subject motion, and suffers from reduced signal-to-noise ratio (SNR). Super-resolution reconstruction (SRR) has recently emerged as a technique that allows for a trade-off between high spatial resolution, high SNR, and short scan duration. Deconvolution-based SRR has recently received significant interest due to the convenience of using the image space. The most critical factor to succeed in deconvolution is the accuracy of the estimated blur kernels that characterize how the image was degraded in the acquisition process. Current methods use handcrafted filters, such as Gaussian filters, to approximate the blur kernels, and have achieved promising SRR results. As the image degradation is complex and varies with different sequences and scanners, handcrafted filters, unfortunately, do not necessarily ensure the success of the deconvolution. We sought to develop a technique that enables accurately estimating blur kernels from the image data itself. We designed a deep architecture that utilizes an adversarial scheme with a generative neural network against its degradation counterparts. This design allows for the SRR tailored to an individual subject, as the training requires the scan-specific data only, i.e., it does not require auxiliary datasets of high-quality images, which are practically challenging to obtain. With this technique, we achieved high-quality brain MRI at an isotropic resolution of 0.125 cubic mm with six minutes of imaging time. Extensive experiments on both simulated low-resolution data and clinical data acquired from ten pediatric patients demonstrated that our approach achieved superior SRR results as compared to state-of-the-art deconvolution-based methods, while in parallel, at substantially reduced imaging time in comparison to direct high-resolution acquisitions.

4DFlowNet: Super-Resolution 4D Flow MRI Using Deep Learning and Computational Fluid Dynamics

4D-flow magnetic resonance imaging (MRI) is an emerging imaging technique where spatiotemporal 3D blood velocity can be captured with full volumetric coverage in a single non-invasive examination. This enables qualitative and quantitative analysis of hemodynamic flow parameters of the heart and great vessels. An increase in the image resolution would provide more accuracy and allow better assessment of the blood flow, especially for patients with abnormal flows. However, this must be balanced with increasing imaging time. The recent success of deep learning in generating super resolution images shows promise for implementation in medical images. We utilized computational fluid dynamics simulations to generate fluid flow simulations and represent them as synthetic 4D flow MRI data. We built our training dataset to mimic actual 4D flow MRI data with its corresponding noise distribution. Our novel 4DFlowNet network was trained on this synthetic 4D flow data and was capable in producing noise-free super resolution 4D flow phase images with upsample factor of 2. We also tested the 4DFlowNet in actual 4D flow MR images of a phantom and normal volunteer data, and demonstrated comparable results with the actual flow rate measurements giving an absolute relative error of 0.6 to 5.8% and 1.1 to 3.8% in the phantom data and normal volunteer data, respectively.

Primed Track: Reliable Volumetric Single-cell Tracking and Lineage Tracing of Living Specimen with Dual-labeling Approaches.

Mammalian embryonic development starts with a single fertilized zygote that develops into a blastocyst embryo consisting of three cell types that evolve into either embryonic or extra-embryonic tissues. Lineage tracing of these cells can provide important information about the molecular and cellular dynamics contributing to fate allocation during early development. While global labeling techniques allow for visualization of all cells at the same time, lineage tracing of cells over several divisions can become complicated due to embryo movement and rotation as well as increasing cell densities. Here, we use green-to-red photoconvertible proteins for both global and sparse labeling of cells of interest in the developing murine embryo. We use primed conversion to achieve precise photoconversion of single nuclei in 4-cell stage embryos followed by volumetric live imaging to capture development up to the blastocyst stage. We developed an image analysis pipeline, called primed Track, that uses the dual labeling strategy for both straightforward segmentation and registration of all cells in the embryo as well as correction of rotational and spatial drift. Together, this strategy allows for reliable and fast tracking and lineage tracing of individual cells, even over increased imaging time intervals that result in a major reduction in data volume, all essential conditions for volumetric long-term imaging techniques.

Accelerated imaging with segmented 2D pulses using parallel imaging and virtual coils.

Large magnetic field inhomogeneity can be a significant cause of spatial flip-angle variation when using ordinary, limited-bandwidth RF pulses. Multidimensional RF pulses are particularly sensitive to inhomogeneity due to their extended pulse length, which decreases their bandwidth. Previously, it was shown that, by breaking a 2D pulse into multiple undersampled k-space segments, the excitation bandwidth can be increased at the expense of increased imaging time. The present study shows how this increased imaging time can be offset by undersampling acquisition k-space in a phase-encoded dimension that is in the direction of excitation segmentation. Data from each segment are viewed as originating from "virtual receive coils" rather than multiple physical coils. The undersampled data are reconstructed using parallel imaging techniques (e.g. as in GRAPPA). The method was tested in vivo with brain imaging at both 3 T and 4 T, and used in conjunction with a 32-channel head coil and conventional GRAPPA on the 3 T data. Relationships with existing techniques and future applications are discussed.

Primed Track, high-fidelity lineage tracing in mouse pre-implantation embryos using primed conversion of photoconvertible proteins.

Accurate lineage reconstruction of mammalian pre-implantation development is essential for inferring the earliest cell fate decisions. Lineage tracing using global fluorescence labeling techniques is complicated by increasing cell density and rapid embryo rotation, which hampers automatic alignment and accurate cell tracking of obtained four-dimensional imaging data sets. Here, we exploit the advantageous properties of primed convertible fluorescent proteins (pr-pcFPs) to simultaneously visualize the global green and the photoconverted red population in order to minimize tracking uncertainties over prolonged time windows. Confined primed conversion of H2B-pr-mEosFP-labeled nuclei combined with light-sheet imaging greatly facilitates segmentation, classification, and tracking of individual nuclei from the 4-cell stage up to the blastocyst. Using green and red labels as fiducial markers, we computationally correct for rotational and translational drift, reduce overall data size, and accomplish high-fidelity lineage tracing even for increased imaging time intervals - addressing major concerns in the field of volumetric embryo imaging.

Left ventricular contractile reserve in stress echocardiography: the bright side of the force.

Stress echocardiography (SE) is based on the detection of regional wall motion abnormalities (RWMA) mirroring a physiologi-cally critical epicardial artery stenosis which determines subendocardial underperfusion. Recently, the core protocol of SE has been enriched by the addition of left ventricular contractile reserve (LVCR) based on force. Changes in force can be caused by microvascular and/or epicardial coronary artery disease, but also by myocardial scar, necrosis, and/or sub-epicardial layer disease. Left ventricular contractile reserve is calculated as the stress-to-rest ratio of force (systolic arterial pressure measured by cuff sphygmomanometer to end-systolic volume determined by two-dimensional echocardiography). In contrast to the ejection fraction, force is not dependent on changes in preload and afterload. Cut-off values for a preserved LVCR are > 2.0 for dobu-tamine or exercise stress and > 1.1 for vasodilators, which are weaker inotropic stimuli. Patients with a "strong" heart (normal LVCR values) have a better outcome than patients with a "weak" heart (reduced LVCR values), and this is the prognostic "bright side of the force," meaning that the prognostic value of force-based contractile reserve is higher than that of ejection fraction-based contractile reserve or RWMA. The addition of force to standard SE based on RWMA detection increases the spectrum of risk stratification without any signifi-cant increase in imaging time and only a slight increase in analysis time. In both ischaemic (with RWMA) and non-ischaemic (without RWMA) hearts, the preserved force is associated with a more benign prognosis. The prospective multicentre interna-tional Stress Echo 2020 trial which started in September 2016 has already recruited > 5000 patients with dual RWMA-force imaging and will systematically test the impact of force on the prognosis within and beyond coronary artery disease, including heart failure and hypertrophic cardiomyopathy.

Whole-brain 3D FLAIR at 7T using direct signal control.

PurposeImage quality obtained for brain imaging at 7T can be hampered by inhomogeneities in the static magnetic field, B0, and the RF electromagnetic field, B1. In imaging sequences such as fluid‐attenuated inversion recovery (FLAIR), which is used to assess neurological disorders, these inhomogeneities cause spatial variations in signal that can reduce clinical efficacy. In this work, we aim to correct for signal inhomogeneities to ensure whole‐brain coverage with 3D FLAIR at 7T.MethodsThe direct signal control (DSC) framework was used to optimize channel weightings applied to the 8 transmit channels used in this work on a pulse‐by‐pulse basis through the echo train in the FLAIR sequences. 3D FLAIR brain images were acquired on 5 different subjects and compared with imaging using a quadrature‐like mode of the transmit array. Precomputed “universal” DSC solutions calculated from a separate set of 5 subjects were also explored.ResultsDSC consistently enabled improved imaging across all subjects, with no dropouts in signal seen over the entire brain volume, which contrasted with imaging in quadrature mode. Further, the universal DSC solutions also consistently improved imaging despite not being optimized specifically for the subject being imaged.Conclusion3D FLAIR brain imaging at 7T is substantially improved using DSC and is able to recover regions of low signal without increasing imaging time or interecho spacing.

ASPECTS discrepancies between CT and MR imaging: analysis and implications for triage protocols in acute ischemic stroke

BackgroundOptimal imaging triage for intervention for large vessel occlusions remains unclear. MR-based imaging provides ischemic core volumes at the cost of increased imaging time. CT Alberta Stroke Program Early CT...

Enhancing the detection of BOLD signal in fMRI by reducing the partial volume effect.

Purpose. To investigate the advantages of reducing the partial volume effect (PVE) to enhance the detection of the BOLD signal in fMRI. Methods. A linear phase term was added in k-space to obtain half-voxel shifting of 64 × 64 T2*-weighted echo-planar images. Three sets of image data shifted in the x, y, and diagonal direction, respectively, are combined with the original 64 × 64 data to form the 128 × 128 voxel-shifted interpolated data. Results. A simulation of a synthetic fMRI dataset shows that the voxel-shifted interpolation (VSI) can increase the t-score up to 50% in single-voxel activations. An fMRI study (n = 7) demonstrates that 20.4% of the interpolated voxels have higher t-scores than their nearest neighboring voxels in the original maps. The average increase of the t-score in these interpolated voxels is 13.3%. Conclusion. VSI yields increased sensitivity in detecting voxel-size BOLD activations, improved spatial accuracy of activated regions, and improved detection of the peak BOLD signal of an activated region. VSI can potentially be used as an alternative to the high-resolution fMRI studies in which reduction in SNR and increase in imaging time become prohibitive.

AB1271 Single field-of-view MRI technique for rheumatoid arthritis clinical trials shortens hand/wrist imaging time

BackgroundMRI is increasingly used in clinical trials of rheumatoid arthritis (RA) because of its broader diagnostic scope and superior sensitivity to change [1-3]. Most trials thus far have used circumferential...

Evaluation of 99mTc-Succimer Dosing in Pediatric Patients

Balancing image quality with radiation dose is a goal with every diagnostic procedure requiring radiation. Our institution compared the dosing of (99m)Tc-labeled succimer, commonly referred to as dimercaptosuccinic acid ((99m)Tc-DMSA), to pediatric patients using 2 methods of calculation, body surface area (BSA, the method we used from 2009 to 2010) and body weight (BW, the method we used in 2011). A retrospective study was conducted in a 230-bed inpatient, tertiary-care academic pediatric hospital to obtain objective data on patients under the age of 17 y who received a renal nuclear medicine procedure with (99m)Tc-DMSA using a 300,000-count parallel image and four 150,000-count pinhole images. Data collection included patient age, sex, height, weight, calculated activity, assayed activity, administered activity, residual syringe activity, imaging time, and notable patient or equipment factors affecting the procedure. Calculated activities based on BSA were higher than calculated activities based on BW. (99m)Tc-DMSA adsorption to the plastic syringes was significant, with a range of 3%-82%. Because of the adsorption, an average of 23.7 MBq (SD, ±31 MBq) was added to the patients' calculated dose when the order was placed. Therefore, assayed activities were significantly higher than calculated activities in both groups. Administered activity correlations to BSA and BW calculations were 0.75 and 0.83, respectively. Administered activities from BSA and BW groups were outside the American College of Radiology (ACR)-recommended guidelines 59% and 45% of the time, respectively. Overall, children less than 2 y old were above the ACR recommendations 80% of the time. There was a poor correlation between administered activity and total imaging time (r = 0.23). Average imaging time overall for 5 planar views was 14.8 min (±7.1 min). Patients receiving less than the ACR-recommended administered activities (<1.85 MBq/kg) had an average increase in imaging time of 4.5 min (±3.4 min). The activity administered to patients was significantly affected by the amount of (99m)Tc-DMSA activity adsorbed to the syringe. Syringe residual should be considered when standardizing (99m)Tc-DMSA imaging protocols and calculating patient dose. Although (99m)Tc-DMSA adsorption was variable, the administered activities correlated with calculated activities. In all but one of our patients, the total imaging time was far less than recommended by the ACR and European Association of Nuclear Medicine guidelines. The study indicates that using the BW calculation of 3.7 MBq/kg resulted in a range of administered activity of 1.85-2.59 MBq/kg. (99m)Tc-DMSA dosing of 3.7 MBq/kg for pinhole imaging should be appropriate for most studies.

Which MRI sequence provides the most accurate estimate of branch pulmonary artery size in children with single ventricle?

Background Accurate evaluation of branch pulmonary artery size in children with single ventricle is important for surgical planning and has prognostic implications after Fontan surgery. Various cardiac MRI sequences are employed to evaluate these sometimes hypoplastic pulmonary arteries, which increases imaging time in anesthetised children. The aim of this study was to evaluate which MRI sequence(s) correlate with angiography measure- ments of pulmonary artery size made at cardiac cathe- terization in children with single ventricle. Methods regression with 95% confidence intervals were used to compare MRI with the gold standard catheterization angiography measurements (p<0.05). Results For the RPA, all MRA measured dimensions correlated well with catheterization angiography (axial r=0.81, cor- onal r=0.89, cross-sectional area r=0.81, p<0.0001), with axial dark blood (r=0.65, p=0.02) and cine diameters (r=0.67, p=0.03) showing modest correlations. In con- trast, LPA through plane PC area correlated best (r=0.73, p=0.02), with modest correlations for axial dark blood (r=0.54, p=0.04), MRA axial diameter (r=0.55, p=0.02), and MRA cross-sectional area (r=0.48, p=0.05). Conclusions In children with single ventricle, MPR contrast enhanced MRA measurements showed the best correlate of RPA size compared to catheterization angiography. However, LPA cross-sectional area from PC flow mea- surements, and not MRA, were the best correlate of LPA measurements. Selection of the most appropriate sequence will provide a more accurate pre-operative evaluation of pulmonary artery size to aid the surgical strategy in this population. Knowledge of this will help tailor protocols to study pulmonary artery size in this population and imaging time may be shortened with this in mind. Funding none.

3DMR osseous reconstructions of the shoulder using a gradient-echo based two-point Dixon reconstruction: a feasibility study

To create 3DMR osseous models of the shoulder similar to 3DCT models using a gradient-echo-based two-point/Dixon sequence. CT and 3TMR examinations of 7 cadaveric shoulders were obtained. Glenoid defects were created in 4 of the cadaveric shoulders. Each MR study included an axial Dixon 3D-dual-echo-time T1W-FLASH (acquisition time of 3 min/30 s). The water-only image data from the Dixon sequence and CT data were post-processed using 3D software. The following measurements were obtained on the shoulders: surface area (SA), height/width of the glenoid and humeral head, and width of the biceps groove. The glenoid defects were measured on imaging and compared with measurements made on en face digital photographs of the glenoid fossae (reference standard). Paired t tests/ANOVA were used to assess the differences between the imaging modalities. The differences between the glenoid and humeral measurements were not statistically significant (cm): glenoid SA 0.12 ± 0.04 (p = 0.45) and glenoid width 0.13 ± 0.06 (p = 0.06) with no difference in glenoid height measurement; humeral head SA 0.07 ± 0.12 (p = 0.42), humeral head height 0.03 ± 0.06 (p = 0.42), humeral head width 0.07 ± 0.06(p = 0.18), and biceps groove width 0.02 ± 0.01 (p = 0.07). The mean/standard deviation difference between the reference standard and 3DMR measurements was 0.25 ± 0.96 %/0.30 ± 0.14 mm; 3DCT 0.25 ± 0.96 /0.75 ± 0.39 mm. There was no statistical difference between the measurements obtained on 3DMR and 3DCT (percentage, p = 0.45; mm, p = 0.20). Accurate 3D osseous models of the shoulder can be produced using a 3D two-point/Dixon sequence and can be added to MR examinations with a minor increase in imaging time, used to quantify glenoid loss, and may eliminate the need for pre-surgical CT examinations.

Investigation of the PSF‐choice method for reduced lipid contamination in prostate MR spectroscopic imaging

The purpose of this work was to evaluate a previously proposed approach that aims to improve the point spread function (PSF) of MR spectroscopic imaging (MRSI) to avoid corruption by lipid signal arising from neighboring voxels. Retrospective spatial filtering can be used to alter the PSF; however, this either reduces spatial resolution or requires extending the acquisition in k-space at the cost of increased imaging time. Alternatively, the method evaluated here, PSF-choice, can modify the PSF localization to reduce the contamination from adjacent lipids by conforming the signal response more closely to the desired MRSI voxel grid. This is done without increasing scan time or degrading SNR of important metabolites. PSF-choice achieves improvements in spatial localization through modifications to the radiofrequency excitation pulses. An implementation of this method is reported for MRSI of the prostate, where it is demonstrated that, in 13 of 16 pilot prostate MRSI scans, intravoxel spectral contamination from lipid was significantly reduced when using PSF-choice. Phantom studies were also performed that demonstrate, compared with MRSI with standard Fourier phase encoding, out-of-voxel signal contamination of spectra was significantly reduced in MRSI with PSF-choice.