Dynamic Magnetic Resonance Imaging Sequences Research Articles

Correlation of Static and Dynamic Magnetic Resonance Imaging Sequences in Evaluation of Temporomandibular Joint Dysfunction

Correlation of Static and Dynamic Magnetic Resonance Imaging Sequences in Evaluation of Temporomandibular Joint Dysfunction

The value of dynamic contrast-enhanced MRI and diffusion-weighted sequence in the evaluation of endometrial lesions

Background/Aim: Endometrial abnormalities represent a diagnostic challenge due to overlapping imaging features with normal endometrium. Aim of this study was to assess accuracy of dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging (MRI) in evaluation of endometrial lesions in comparison with T2 and to assess local staging validity and degree of myometrial invasion in malignancy. Methods: Forty patients with abnormal vaginal bleeding or sonographic thickened endometrial were recruited. MRI examination of pelvis was per-formed using 1.5 T scanner with a pelvic array coil. Conventional T1-and T2, dynamic contrast-enhanced (DCE) sequences and diffusion-weighted image (DWI) were performed. Results: Mean age of patients was 53.2 years and 60 % of patients COM-plained of post-menopausal bleeding. Irregular margin, type III enhancement curve, a high signal in T2WI and DWI and low signal of apparent diffusion coefficient (ADC) were significantly associated with malignancy. The optimum ADC threshold value for distinguishing benign from malignant endometrial lesions was 0.905 × 10 -3 mm 2 /S, with 95.5 % sensitivity and 92.9 % specificity. DWI was most sensitive to malignant endometrial lesions, followed by DCE (89.6 %, 98.4 %) and T2 (86.7 %, 91.4 %). DWI and DCE staging correlated with FIGO staging (p = 0.0001 and p = 0.019, respectively). DWI had the best sensitivity for myometrial invasion (95.6 %), followed by DCE (91.9 %) and T2WI (90.1 %). All three sequences had 89.7 % specificity. Conclusion: DWI and DCE MRI were superior to conventional MRI at distinguishing malignant from benign endometrial lesions and can improve myometrial invasion depth evaluation and therapy planning when COM-bined with morphological T2WI. ADC cutoff at a high b value improved MRI diagnostic sensitivity and specificity.

MRI of the pelvic floor in female patients with stress urinary incontinence, pre- and postoperative and/or physiotherapy: analysis of the defect-specific approach

BackgroundStress urinary incontinence (SUI) is a common disabling pelvic floor dysfunction, particularly among aging women. Magnetic resonance imaging (MRI) with dynamic sequences has been proven reliable for detecting pelvic floor weaknesses, especially with multiple compartments defects. Since surgical and non-surgical management options exist, detailed imaging analysis and comprehension of the various surgical and non-surgical interventions are crucial for surgical planning and postoperative evaluation. However, patients often present with recurrent or new symptoms after surgery, where MR imaging is necessary to detect complications in this setting. We aimed to analyze MR images pre- and postoperative/intervention using the defect-specific approach aiming at better understanding of the underlying complication and/or the cause of recurrence.ResultsThirty female patients with SUI were included in the study; 20 underwent surgery, 6 were treated by physiotherapy only, while 3 patients underwent both surgery and physiotherapy and 1 patient was treated conservatively. According to their clinical symptoms, patients with successful surgical/physiotherapy outcome were 18 cases (60%), while unsuccessful group comprised of 12 cases (40%) is classified as follows: persistent complaints subgroup 7 patients (23.3%), de novo complaint subgroup 2 patients (6.7%), while the complicated subgroup is comprised of 2 patients (6.7%) and the persistent/de novo complaints subgroup of the unsuccessful group is composed of 1 case (3.3%). They all underwent MRI of the pelvic floor with a standardized technique, pre- and postoperative/physiotherapy. Changes in level III endopelvic fascia defects between the pre- and postoperative/physiotherapy studies were statistically significant (p = 0.045). Urinary bladder and uterine descent were also found statistically significant between the pre- and postoperative/physiotherapy studies (p = 0.001 and p = 0.029, respectively). Comparing successful and unsuccessful groups pre- and postoperative/therapy, levator plate angle (LPA) was found statistically significant as well (p = 0.039 preoperative and p = 0.001 postoperative).ConclusionsAnalysis of the pre- and postoperative static and dynamic MRI sequences along with proper understanding of the preformed intervention can pinpoint the underlying pathology leading to the recurrent or de novo symptom and/or complications. The defect-specific approach can help determine the underlying pelvic floor defect by altering the MRI techniques tailored for each patient according to their complaint.

Dynamic Liver Magnetic Resonance Imaging During Free Breathing: A Feasibility Study With a Motion Compensated Variable Density Radial Acquisition and a Viewsharing High-Pass Filtering Reconstruction.

Robust dynamic contrast-enhanced T1-weighted images are crucial for accurate detection and categorization of focal liver lesions in liver/abdominal magnetic resonance imaging (MRI). As optimal dynamic imaging usually requires multiple breath-holds, its inherent susceptibility to motion artifacts frequently results in degraded image quality in incompliant patients. Because free-breathing imaging may overcome this drawback, the intention of this study was to evaluate a dynamic MRI sequence acquired during free breathing using the variable density, elliptical centric golden angle radial stack-of-stars radial sampling scheme, which so far has not been implemented in 4-dimensional applications. In a prospective pilot study, 27 patients received a routine abdominal MRI protocol including the prototype free-breathing sequence (4DFreeBreathing) for dynamic imaging. This enables more convenient and faster reconstruction through variable density, elliptical centric golden angle radial stack-of-stars without the use of additional reconstruction hardware, and even higher motion robustness through soft-gating. A standard breath-hold sequence performed subsequently served as reference standard. Of the continuous dynamic data sets, each dynamic phase was analyzed regarding image quality, motion artifacts and vessel conspicuity using 5-point Likert scales. Furthermore, correct timing of the late arterial phase was compared with the preexaminations. 4DFreeBreathing delivered motion-free dynamic images with high temporal resolution in each subject. Overall image quality scores were rated good or excellent for 4DFreeBreathing and the gold standard without significant differences (P = 0.34). There were significantly less motion artifacts in the 4DFreeBreathing sequence (P < 0.0001), whereas vessel conspicuity in each dynamic phase was comparable for both groups (P = 0.45, P > 0.99, P = 0.22, respectively). Correct timing of the late arterial phase could be achieved in 27 of 27 (100%) examinations using 4DFreeBreathing versus 35 of 53 (66%) preexaminations using gold standard (P < 0.001). The benefit of convenient and fast image reconstruction combined with the superiority in motion robustness and timing compared with standard breath hold sequences renders 4DFreeBreathing an attractive alternative to existing free-breathing techniques in dynamic liver MRI.

Time-Dependent Deep Image Prior for Dynamic MRI.

We propose a novel unsupervised deep-learning-based algorithm for dynamic magnetic resonance imaging (MRI) reconstruction. Dynamic MRI requires rapid data acquisition for the study of moving organs such as the heart. We introduce a generalized version of the deep-image-prior approach, which optimizes the weights of a reconstruction network to fit a sequence of sparsely acquired dynamic MRI measurements. Our method needs neither prior training nor additional data. In particular, for cardiac images, it does not require the marking of heartbeats or the reordering of spokes. The key ingredients of our method are threefold: 1) a fixed low-dimensional manifold that encodes the temporal variations of images; 2) a network that maps the manifold into a more expressive latent space; and 3) a convolutional neural network that generates a dynamic series of MRI images from the latent variables and that favors their consistency with the measurements in k -space. Our method outperforms the state-of-the-art methods quantitatively and qualitatively in both retrospective and real fetal cardiac datasets. To the best of our knowledge, this is the first unsupervised deep-learning-based method that can reconstruct the continuous variation of dynamic MRI sequences with high spatial resolution.

A 3D cine-MRI acquisition technique and image analysis framework to quantify bowel motion demonstrated in gynecological cancer patients.

PurposeMagnetic resonance imaging (MRI) is increasingly used in radiation oncology for target delineation and radiotherapy treatment planning, for example, in patients with gynecological cancers. As a consequence of pelvic radiotherapy, a part of the bowel is irradiated, yielding risk of bowel toxicity. Existing dose‐effect models predicting bowel toxicity are inconclusive and bowel motion might be an important confounding factor. The exact motion of the bowel and dosimetric effects of its motion are yet uncharted territories in radiotherapy. In diagnostic radiology methods on the acquisition of dynamic MRI sequences were developed for bowel motility visualization and quantification. Our study aim was to develop an imaging technique based on three‐dimensional (3D) cine‐MRI to visualize and quantify bowel motion and demonstrate it in a cohort of gynecological cancer patients.MethodsWe developed an MRI acquisition suitable for 3D bowel motion quantification, namely a balanced turbo field echo sequence (TE = 1.39 ms, TR = 2.8 ms), acquiring images in 3.7 s (dynamic) with a 1.25 × 1.25 × 2.5 mm3 resolution, yielding a field of view of 200 × 200 × 125 mm3. These MRI bowel motion sequences were acquired in 22 gynecological patients. During a 10‐min scan, 160 dynamics were acquired. Subsequent dynamics were deformably registered using a B‐spline transformation model, resulting in 159 3D deformation vector fields (DVFs) per MRI set. From the 159 DVFs, the average vector length was calculated per voxel to generate bowel motion maps. Quality assurance was performed on all 159 DVFs per MRI, using the Jacobian Determinant and the Harmonic Energy as deformable image registration error metrics. In order to quantify bowel motion, we introduced the concept of cumulative motion–volume histogram (MVH) of the bowel bag volume. Finally, interpatient variation of bowel motion was analyzed using the MVH parameters M10%, M50%, and M90%. The M10%/M50%/M90% represents the minimum bowel motion per frame of 10%/50%/90% of the bowel bag volume.ResultsThe motion maps resulted in a visualization of areas with small and large movements within the bowel bag. After applying quality assurance, the M10%, M50%, and M90% were 4.4 (range 2.2–7.6) mm, 2.2 (range 0.9–4.1) mm, and 0.5 (range 0.2–1.4) mm per frame, on average over all patients, respectively.ConclusionWe have developed a method to visualize and quantify 3D bowel motion with the use of bowel motion specific MRI sequences in 22 gynecological cancer patients. This 3D cine‐MRI‐based quantification tool and the concept of MVHs can be used in further studies to determine the effect of radiotherapy on bowel motion and to find the relation with dose effects to the small bowel. In addition, the developed technique can be a very interesting application for bowel motility assessment in diagnostic radiology.

Dynamic Fast Imaging Employing Steady State Acquisition Magnetic Resonance Imaging of the Vocal Tract in One Overtone Male Singer: Our Preliminary Experience

To demonstrate physiological changing of vocal tract's structures during overtone singing with commercial magnetic resonance imaging (MRI) Fast Imaging Employing Steady State Acquisition (FIESTA) dynamic sequence. A 1.5 T MRI with a 16 channel head-and-neck coil and a FIESTA sequence were used. A temporal resolution of 0.155 sec (7 image/s). A single professional singer was studied. The MR acquisition is made while the singer performed a predetermined singing sequence. Three different overtone singing techniques were examined (L-technique, J-technique, and NG technique) and one effect (Ezengileer) applied to L-technique. For each overtone technique we evaluated MRI movement of lips, tongue, velopharyngeal closure, and relationship among tongue and pharyngeal posterior wall/soft palate. To cancel the noise over-imposed, the dynamic MRI was subsequently dubbed in studio with the audio of the preset overtone sing. Dubbed MR images were analyzed with an Overtone Analyzer Software and different sound frequencies were identified and pointed out as colored lines. This study shows that different overtone techniques are related to a specific conformation of tongue, lips, soft and hard palate and motion's relation changing between them. Only a correct conformation of vocal tract's structure allows resonance and so to hear desired fundamental and harmonic pitch in overtone singing. The preliminary data of our study demonstrates that FIESTA dynamic MRI sequence can be used to depict changing of position of vocal tract's structure in overtone singing techniques with a good temporal and anatomic resolution.

Subsampled brain MRI reconstruction by generative adversarial neural networks.

A main challenge in magnetic resonance imaging (MRI) is speeding up scan time. Beyond improving patient experience and reducing operational costs, faster scans are essential for time-sensitive imaging, such as fetal, cardiac, or functional MRI, where temporal resolution is important and target movement is unavoidable, yet must be reduced. Current MRI acquisition methods speed up scan time at the expense of lower spatial resolution and costlier hardware. We introduce a practical, software-only framework, based on deep learning, for accelerating MRI acquisition, while maintaining anatomically meaningful imaging. This is accomplished by MRI subsampling followed by estimating the missing k-space samples via generative adversarial neural networks. A generator-discriminator interplay enables the introduction of an adversarial cost in addition to fidelity and image-quality losses used for optimizing the reconstruction. Promising reconstruction results are obtained from feasible sampling patterns of up to a fivefold acceleration of diverse brain MRIs, from a large publicly available dataset of healthy adult scans as well as multimodal acquisitions of multiple sclerosis patients and dynamic contrast-enhanced MRI (DCE-MRI) sequences of stroke and tumor patients. Clinical usability of the reconstructed MRI scans is assessed by performing either lesion or healthy tissue segmentation and comparing the results to those obtained by using the original, fully sampled images. Reconstruction quality and usability of the DCE-MRI sequences is demonstrated by calculating the pharmacokinetic (PK) parameters. The proposed MRI reconstruction approach is shown to outperform state-of-the-art methods for all datasets tested in terms of the peak signal-to-noise ratio (PSNR), the structural similarity index (SSIM), as well as either the mean squared error (MSE) with respect to the PK parameters, calculated for the fully sampled DCE-MRI sequences, or the segmentation compatibility, measured in terms of Dice scores and Hausdorff distance. The code is available on GitHub.

Real-time dynamic 3-T MRI assessment of spine kinematics: a feasibility study utilizing three different fast pulse sequences.

Half-Fourier acquisition single-shot turbo spin-echo (HASTE), continuous radial gradient-echo (GRE), and True FISP allow real-time dynamic assessment of the spine. To evaluate the feasibility of adding dynamic sequences to routine spine magnetic resonance imaging (MRI) for assessment of spondylolisthesis. Retrospective review was performed of patients referred for dynamic MRI of the cervical or lumbar spine between January 2017 and 2018 who had flexion-extension radiographs within two months of MRI. Exclusion criteria were: incomplete imaging; spinal hardware; and inability to tolerate dynamic examination. Blinded, independent review by two board-certified musculoskeletal radiologists was performed to assess for spondylolisthesis (>3 mm translation); consensus review of dynamic radiographs served as the gold standard. Cervical spinal cord effacement was assessed. Inter-reader agreement and radiographic concordance was calculated for each sequence. Twenty-one patients were included (8 men, 13 women; mean age 47.9 ± 16.5 years). Five had MRI of the cervical spine and 16 had MRI of the lumbar spine. Mean acquisition time was 18.4 ± 1.7 min with dynamic sequences in the range of 58-77 s. HASTE and True FISP had the highest inter-reader reproducibility (κ = 0.88). Reproducibility was better for the lumbar spine (κ = 0.94) than the cervical spine (κ = 0.28). Sensitivity of sequences for spondylolisthesis was in the range of 68.8%-78.6%. All three sequences had high accuracy levels: ≥90.5% averaged across the cervical and lumbar spine. Cervical cord effacement was observed during dynamic MRI in two cases (100% agreement). Real-time dynamic MRI sequences added to spine MRI protocols provide reliable and accurate assessment of cervical and lumbar spine spondylolisthesis during flexion and extension.

Post-treatment prostate MRI.

Accurate early detection of recurrent prostate cancer after surgical or nonsurgical treatment is increasingly relevant in the era of evolving options for salvage therapy. The importance of differentiating between local tumor recurrence, distant metastatic disease, and a combination of both in a patient with biochemical recurrence of prostate cancer is essential for appropriate treatment selection. Magnetic resonance imaging (MRI) is the best test for localization and characterization of locally residual or recurrent prostate cancer. It is essential for the radiologist involved in prostate MRI interpretation to be familiar with key imaging findings and advantages of different sequences to reach a confident diagnosis in the post-treatment setting. In this pictorial review, we present imaging findings of post-treatment prostate MRI including expected post-treatment anatomy and imaging characteristics, and the typical appearances of local tumor recurrence after radical prostatectomy, radiation therapy, and focal therapy for prostate cancer. While a multi-parametric MRI approach remains key just as in the treatment-naïve gland, this review emphasizes the much greater importance of the dynamic contrast-enhanced MRI sequence for evaluation in the post-treatment setting.

Motion Compensated Dynamic MRI Reconstruction With Local Affine Optical Flow Estimation.

This paper proposes a novel framework to reconstruct dynamic magnetic resonance imaging (DMRI) with motion compensation (MC). Specifically, by combining the intensity-based optical flow constraint with the traditional compressed sensing scheme, we are able to jointly reconstruct the DMRI sequences and estimate the interframe motion vectors. Then, the DMRI reconstruction can be refined through MC with the estimated motion field. By employing the coarse-to-fine multi-scale resolution strategy, we are able to update the motion field in different spatial scales. The estimated motion vectors need to be interpolated to the finest resolution scale to compensate the DMRI reconstruction. Moreover, the proposed framework is capable of handling a wide class of prior information (regularizations) for DMRI reconstruction, such as sparsity, low rank, and total variation. The formulated optimization problem is solved by a primal-dual algorithm with linesearch due to its efficiency when dealing with non-differentiable problems. Experiments on various DMRI datasets validate the reconstruction quality improvement using the proposed scheme in comparison to several state-of-the-art algorithms.

Assessment of vocal fold mobility using dynamic magnetic resonance imaging and ultrasound in healthy volunteers.

PurposeTo verify the value of dynamic magnetic resonance imaging (MRI) sequences, fast field echo (FFE), and balanced gradient echo (true fast imaging with steady-state free precession – TRUFI) in the evaluation of vocal fold mobility in healthy volunteers, against ultrasound examination (US) as the reference test.Material and methodsVocal fold mobility in 35 healthy volunteers (age 20-59 years, 20 women and 15 men) with no history of laryngeal disorders and neck surgeries was determined by means of US and MRI during normal breathing and phonation of the “hiiii” sound. US images were used to determine the glottic angles. During MRI two dynamic sequences, fast field echo and balanced gradient echo, were applied to determine the minimum and maximum values of the glottic angles, along with the rima glottidis area, separately for the right and left compartments. Due to differences in larynx anatomy, the abovementioned parameters were analysed separately for women and men.ResultsNo significant differences were observed between the glottic angle values obtained during US and dynamic MRI (FFE and TRUFI sequences). Regardless of the dynamic MRI sequence used, a positive correlation was found between the maximum values of glottic angle and the rima glottidis area. This correlation was strong and statistically significant among men, but not in women.ConclusionsDynamic MRI of vocal folds using FFE and TRUFI sequence is an accurate method for the objective evaluation of rima glottidis width.

A Novel Reconstruction Approach Combining Global and Local Low-rank Constraints for Undersampled Dynamic MRI

Background: Dynamic Magnetic Resonance Imaging (MRI) can be used to diagnose organs’ motion, so it is useful and has been used widely. Reconstructing dynamic MRI from undersampled measurements can accelerate the imaging speed, this has attracted the attention of many researchers. For dynamic MRI, there is much global and local correlation in spatial and temporal dimensions, and if the spatial and temporal redundancy can be utilized efficiently in the reconstruction process, higher spatial and temporal resolutions can be achieved. Methods: In this paper, we propose a novel reconstruction method which utilizes the redundancy in spatial and temporal domains jointly. In particular, a 2-D matrix is obtained by vectorizing the images of every frame of a 3-D dynamic MRI sequence, and we extract overlapping 2-D patches from this matrix. Similar patches will be searched from these 2-D patches, and a non-convex function is used to approximate the low-rank matrices formed by these similar patches. At the present stage, only local correlation in the temporal dimension is employed. Discussion: To obtain better image quality, the global correlation in the temporal dimension is utilized by a low-rank penalty which is relaxed by the nuclear norm. Conclusion: We validate the proposed algorithm by using retrospectively undersampled in vivo cardiac datasets, and the proposed algorithm shows superior reconstruction performance compared to existing state-of-the-art methods such as k-t FOCUSS, k-t SLR, and L+S. Keywords: Dynamic MRI, correlation, similar patches, low-rank constraint, non-convex function, image reconstruction.

Reducing Navigators in Free-Breathing Abdominal MRI via Temporal Interpolation Using Convolutional Neural Networks.

Navigated 2-D multi-slice dynamic magnetic resonance imaging (MRI) acquisitions are essential for MR guided therapies. This technique yields time-resolved volumetric images during free-breathing, which are ideal for visualizing and quantifying breathing induced motion. To achieve this, navigated dynamic imaging requires acquiring multiple navigator slices. Reducing the number of navigator slices would allow for acquiring more data slices in the same time, and hence, increasing through-plane resolution or alternatively the overall acquisition time can be reduced while keeping resolution unchanged. To this end, we propose temporal interpolation of navigator slices using convolutional neural networks (CNNs). Our goal is to acquire fewer navigators and replace the missing ones with interpolation. We evaluate the proposed method on abdominal navigated dynamic MRI sequences acquired from 14 subjects. Investigations with several CNN architectures and training loss functions show favorable results for cost and a simple feed-forward network with no skip connections. When compared with interpolation by non-linear registration, the proposed method achieves higher interpolation accuracy on average as quantified in terms of root mean square error and residual motion. Analysis of the differences shows that the better performance is due to more accurate interpolation at peak exhalation and inhalation positions. Furthermore, the CNN-based approach requires substantially lower execution times than that of the registration-based method. At last, experiments on dynamic volume reconstruction reveal minimal differences between reconstructions with acquired and interpolated navigator slices.

Interactive iterative relative fuzzy connectedness lung segmentation on thoracic 4D dynamic MR images.

Lung delineation via dynamic 4D thoracic magnetic resonance imaging (MRI) is necessary for quantitative image analysis for studying pediatric respiratory diseases such as thoracic insufficiency syndrome (TIS). This task is very challenging because of the often-extreme malformations of the thorax in TIS, lack of signal from bone and connective tissues resulting in inadequate image quality, abnormal thoracic dynamics, and the inability of the patients to cooperate with the protocol needed to get good quality images. We propose an interactive fuzzy connectedness approach as a potential practical solution to this difficult problem. Manual segmentation is too labor intensive especially due to the 4D nature of the data and can lead to low repeatability of the segmentation results. Registration-based approaches are somewhat inefficient and may produce inaccurate results due to accumulated registration errors and inadequate boundary information. The proposed approach works in a manner resembling the Iterative Livewire tool but uses iterative relative fuzzy connectedness (IRFC) as the delineation engine. Seeds needed by IRFC are set manually and are propagated from slice-to-slice, decreasing the needed human labor, and then a fuzzy connectedness map is automatically calculated almost instantaneously. If the segmentation is acceptable, the user selects "next" slice. Otherwise, the seeds are refined and the process continues. Although human interaction is needed, an advantage of the method is the high level of efficient user-control on the process and non-necessity to refine the results. Dynamic MRI sequences from 5 pediatric TIS patients involving 39 3D spatial volumes are used to evaluate the proposed approach. The method is compared to two other IRFC strategies with a higher level of automation. The proposed method yields an overall true positive and false positive volume fraction of 0.91 and 0.03, respectively, and Hausdorff boundary distance of 2 mm.

Multiorgan motion tracking in dynamic magnetic resonance imaging for evaluation of pelvic system mobility and shear strain

AbstractFemale pelvic disorders have a large social impact; the diagnosis of which relies on a key indication: pelvic mobility. The normal mobility is present in a healthy patient, meanwhile the hypermobility can be a sign of female pelvic prolapse and the hypomobility for endometriosis. The evaluation of pelvic mobility is based on medical image analysis. However, the latter does not provide precise values of these indicators directly. Moreover, suspension devices play an important role in pelvic organ function but can hardly be observed on medical images. Our objective is to propose an image‐based analysis tool for the quantitative evaluation of pelvic mobility and the shear strain which has an impact on suspension devices. Hence, this paper introduces a such tool based on an efficient and semiautomatic motion tracking of multiple pelvic organs: the bladder, vagina, and rectum presented in dynamic magnetic resonance imaging sequences. The method was validated on prototypical images and applied to different mobility cases. The computed displacement and shear strain fields provide important information on the quality of suspension devices between organs for a fine diagnosis in the clinical context, for example, the early diagnosis of female pelvic prolapse and the localization of possible lesion areas before surgery. Meanwhile, the predicted mobility can be used to compare with the finite element model for numerical simulation.

Role of PI-RADSv2 with multiparametric MRI in determining who needs active surveillance or definitive treatment according to PRIAS.

To evaluate the role of Prostate Imaging Reporting and Data System v. 2 (PI-RADSv2) in triaging patients with prostate cancer according to Prostate Cancer Research International: Active Surveillance (PRIAS). Between January 2012 and December 2014, 456 patients with biopsy-proven cancer underwent multiparametric 3T magnetic resonance imaging (MRI) using T2 -weighted, diffusion-weighted, and dynamic contrast-enhanced MRI sequences, and then radical prostatectomy. Two radiologists independently reviewed MR images using PI-RADSv2. For AS, PRIAS required clinical stage <T3, prostate-specific antigen (PSA) ≤10 ng/mL, PSA density <0.2 ng/mL2 , Gleason score (GS) ≤6, and the number of positive cores ≤2. For AS, PI-RADSv2 required an index lesion scored <4. Standard reference was prostatectomy, in which insignificant cancer was defined as a small (<0.5 cm3 ) organ-confined lesion with GS ≤6. Sensitivity and specificity for insignificant cancer were obtained with PRIAS, PI-RADSv2, and both. The sensitivity and specificity with PRIAS were 82.9% (68/82) and 70.9% (265/374), respectively. PI-RADSv2 decreased the sensitivity to 61% (50/82) to 80.5% (66/82), but increased the specificity to 77.8% (291/374) to 90.8% (340/374). The combination of PRIAS and PI-RDASv2 increased significantly the specificity to 89.6% (335/374) to 92.8% (347/374) (P < 0.001). PRIAS using multiparametric MRI can identify a greater number of insignificant cancers than PI-RADSv2. However, PI-RADSv2 helps detect many significant cancers that are misdiagnosed as insignificant cancer with PRIAS. 3 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;45:1753-1759.

Quantification of Pelvic Mobility on Dynamic Magnetic Resonance Images: Using Mechanical Insight to Help Diagnose Pelvic Pathologies

AbstractPelvic mobility is essential for good pelvic organ function. Any modification may be a sign of pathology. The objective of this study was to define a methodology to quantify pelvic mobility. An analysis protocol based on an image registration technique performed on dynamic magnetic resonance imaging sequences is presented. A methodology is proposed for measuring and analysing the whole displacement field based on the contour of the four pelvic organs: the vagina, bladder, rectum and uterus. A targeted analysis of pelvic mobility can be applied in the normal, hypermobility and hypomobility context. The quantification of pelvic mobility in normal conditions allows localising fascia or ligaments involved in the static of pelvic organs. In pathological situations such as prolapse, it helps localise a suspension structure weakness. In a context of hypomobility such as deep pelvic endometriosis, it should help localise pathologic areas to provide more relevant diagnosis and treatment. When combined with conventional radiology, this analysis protocol can be applied to the diagnosis and assessment of complex pelvic pathologies to help define the most suitable surgery. Moreover, these experimental results obtained in normal and pathological cases will help build and validate a better mechanical finite element model of the pelvic system.

Pelvic Floor Failure: MR Imaging Evaluation of Anatomic and Functional Abnormalities

Pelvic floor failure is a common disorder that can seriously jeopardize a woman's quality of life by causing urinary and fecal incontinence, difficult defecation, and pelvic pain. Multiple congenital and acquired risk factors are associated with pelvic floor failure, including altered collagen metabolism, female sex, vaginal delivery, menopause, and advanced age. A complex variety of fascial and muscular lesions that range from stretching, insertion detachment, denervation atrophy, and combinations of pelvic floor relaxation to pelvic organ prolapse may manifest in a single patient. Thorough preoperative assessment of pelvic floor failure is necessary to reduce the rate of relapse, which is reported to be as high as 30%. Magnetic resonance (MR) imaging of the pelvic floor is a two-step process that includes analysis of anatomic damage on axial fast spin-echo (FSE) T2-weighted images and functional evaluation using sagittal dynamic single-shot T2-weighted sequences during straining and defecation. This article presents high-resolution FSE T2-weighted MR images that permit detailed assessment of anatomic lesions and briefly describes pelvic floor pathophysiology, associated clinical symptoms, and patterns of dysfunction seen with dynamic MR imaging sequences. MR imaging is a powerful tool that enables radiologists to comprehensively evaluate pelvic anatomic and functional abnormalities, thus helping surgeons provide appropriate treatment and avoid repeat operations.

Compressed Sensing Based Real-Time Dynamic MRI Reconstruction

This work addresses the problem of real-time online reconstruction of dynamic magnetic resonance imaging sequences. The proposed method reconstructs the difference between the previous and the current image frames. This difference image is sparse. We recover the sparse difference image from its partial k-space scans by using a nonconvex compressed sensing algorithm. As there was no previous fast enough algorithm for real-time reconstruction, we derive a novel algorithm for this purpose. Our proposed method has been compared against state-of-the-art offline and online reconstruction methods. The accuracy of the proposed method is less than offline methods but noticeably higher than the online techniques. For real-time reconstruction we are also concerned about the reconstruction speed. Our method is capable of reconstructing 128 × 128 images at the rate of 6 frames/s, 180 × 180 images at the rate of 5 frames/s and 256 × 256 images at the rate of 2.5 frames/s.