MRI Pulse Sequences Research Articles

Simultaneous proton resonance frequency T1 - MR shear wave elastography for MR-guided focused ultrasound multiparametric treatment monitoring.

To develop an efficient MRI pulse sequence to simultaneously measure multiple parameters that have been shown to correlate with tissue nonviability following thermal therapies. A 3D segmented EPI pulse sequence was used to simultaneously measure proton resonance frequency shift (PRFS) MR thermometry (MRT), T1 relaxation time, and shear wave velocity induced by focused ultrasound (FUS) push pulses. Experiments were performed in tissue mimicking gelatin phantoms and ex vivo bovine liver. Using a carefully designed FUS triggering scheme, a heating duty cycle of approximately 65% was achieved by interleaving FUS ablation pulses with FUS push pulses to induce shear waves in the tissue. In phantom studies, temperature increases measured with PRFS MRT and increases in T1 correlated with decreased shear wave velocity, consistent with material softening with increasing temperature. During ablation in ex vivo liver, temperature increase measured with PRFS MRT initially correlated with increasing T1 and decreasing shear wave velocity, and after tissue coagulation with decreasing T1 and increasing shear wave velocity. This is consistent with a previously described hysteresis in T1 versus PRFS curves and increased tissue stiffness with tissue coagulation. An efficient approach for simultaneous and dynamic measurements of PRSF, T1 , and shear wave velocity during treatment is presented. This approach holds promise for providing co-registered dynamic measures of multiple parameters, which correlates to tissue nonviability during and following thermal therapies, such as FUS.

Effect of Averaging Measurements From Multiple MRI Pulse Sequences on Kidney Volume Reproducibility in Autosomal Dominant Polycystic Kidney Disease.

Total kidney volume (TKV) is an important biomarker for assessing kidney function, especially for autosomal dominant polycystic kidney disease (ADPKD). However, TKV measurements from a single MRI pulse sequence have limited reproducibility, ± ~5%, similar to ADPKD annual kidney growth rates. To improve TKV measurement reproducibility on MRI by extending artificial intelligence algorithms to automatically segment kidneys on T1-weighted, T2-weighted, and steady state free precession (SSFP) sequences in axial and coronal planes and averaging measurements. Retrospective training, prospective testing. Three hundred ninety-seven patients (356 with ADPKD, 41 without), 75% for training and 25% for validation, 40 ADPKD patients for testing and 17 ADPKD patients for assessing reproducibility. T2-weighted single-shot fast spin echo (T2), SSFP, and T1-weighted 3D spoiled gradient echo (T1) at 1.5 and 3T. 2D U-net segmentation algorithm was trained on images from all sequences. Five observers independently measured each kidney volume manually on axial T2 and using model-assisted segmentations on all sequences and image plane orientations for two MRI exams in two sessions separated by 1-3 weeks to assess reproducibility. Manual and model-assisted segmentation times were recorded. Bland-Altman, Schapiro-Wilk (normality assessment), Pearson's chi-squared (categorical variables); Dice similarity coefficient, interclass correlation coefficient, and concordance correlation coefficient for analyzing TKV reproducibility. P-value < 0.05 was considered statistically significant. In 17 ADPKD subjects, model-assisted segmentations of axial T2 images were significantly faster than manual segmentations (2:49 minute vs. 11:34 minute), with no significant absolute percent difference in TKV (5.9% vs. 5.3%, P=0.88) between scans 1 and 2. Absolute percent differences between the two scans for model-assisted segmentations on other sequences were 5.5% (axial T1), 4.5% (axial SSFP), 4.1% (coronal SSFP), and 3.2% (coronal T2). Averaging measurements from all five model-assisted segmentations significantly reduced absolute percent difference to 2.5%, further improving to 2.1% after excluding an outlier. Measuring TKV on multiple MRI pulse sequences in coronal and axial planes is practical with deep learning model-assisted segmentations and can improve TKV measurement reproducibility more than 2-fold in ADPKD. 2 TECHNICAL EFFICACY: Stage 1.

Pulse Sequences and Reconstruction in Fast MR Imaging of the Liver.

The liver moves with respiratory motion. Respiratory motion causes image artifacts as MRI is a motion-sensitive imaging modality; thus, MRI scan speed improvement has been an important technical development target for liver MRI for years. Recent pulse sequence and image reconstruction technology advancement has realized a fast liver MRI acquisition method. Such new technologies allow us to obtain liver MRI in a shorter time, particularly, within breath-holding time. Other benefits of new the technology and the higher spatial resolution liver MRI within a given scan time are improved slice coverage and smaller pixel size. In this review, MRI pulse sequence and reconstruction technologies to accelerate scan speed for T1- and T2-weighted liver MRI will be discussed. Technologies that reduce scan time while keeping image contrast, SNR and image spatial resolution are needed for fast MRI acquisition. We will discuss the progress of MRI acquisition methods, the enabling technology, established applications, current trends, and the future outlook.

Arterial Spin Labeling: Techniques, Clinical Applications, and Interpretation.

Arterial spin labeling (ASL) is an emerging noninvasive MRI technique for assessing cerebral perfusion. An important advantage of ASL perfusion is the lack of a requirement for an exogenous tracer. ASL uses magnetically labeled water protons from arterial blood as an endogenous diffusible tracer. For this reason, ASL is an attractive perfusion imaging modality for children and for patients with contraindications or adverse reactions to gadolinium, patients with renal failure, and those who need repeated follow-up imaging. Another advantage of ASL is the possibility of quantifying cerebral blood flow, which provides an opportunity for comparative analysis among multiple longitudinal studies, unlike other MR perfusion techniques, which are semiquantitative and yield relative perfusion parameters. Advances in MRI technology and pulse sequence design have translated ASL beyond the research arena to successful clinical implementation. However, ASL is still underused in routine clinical practice. Some disadvantages of ASL include a lower signal-to-noise ratio and a longer acquisition time than those with dynamic susceptibility contrast-enhanced MRI. Additional factors limiting the use of ASL include variations in existing techniques and pulse sequence design, the complexity of implementation and postprocessing, insufficient experience with and/or knowledge of the potential clinical applications, and the absence of interpretation guidelines. The authors review the technical and physiologic basis of ASL perfusion, as well as artifacts, pitfalls, and its current clinical applications. A practical approach for interpreting ASL findings is also suggested.

A New Approach for Native Myocardial T1 mapping using a standard Single-shot MRI pulse sequence technique.

Cardiovascular magnetic resonance (CMR) diagnosis of acute myocarditis (AM) requires contrast injection in Late Gadolinium Enhancement (LGE). Native T1- mapping has been suggested as a potentially helpful technique in connection to the quantitative assessment of cardiac anomalies. This was demonstrated utilizing particular sequences, which are manufacturer-specific and not practicable on all machines. In this study, we propose to evaluate the capability of a standard, single-shot sequence in the clinical context to distinguish between healthy myocardium and diffuse disease. For this, 30 patients (22 participants with no cardiac involvement and 8 patients with verified cardiac involvement based on echocardiographic criteria and Troponin levels) received CMR (3-T) with LGE imaging. This analysis revealed that cardiac T1 times were significantly higher in patients with myocarditis (1516± 29ms), myocardial infarction (1596± 98ms), and pericardial effusion (1217± 12ms) than in healthy subjects (1117± 15ms). Furthermore, in roughly 2 minutes, our model reconstruction allows for single-shot myocardial T1 maps with great spatial resolution, precision, accuracy, and consistency. As it underlined the importance of T1 mapping in clinical application improvement and its contribution to direct assessment of cardiac system anomalies

T1 relaxation of bound and pore water in cortical bone.

MRI measures of bound and/or pore water concentration in cortical bone offer potential diagnostics of bone fracture risk. The transverse relaxation characteristics of both bound and pore water are relatively well understood and have been used to design clinical MRI pulse sequences to image each water pool quantitatively. However, these methods are also sensitive to longitudinal relaxation characteristics, which have been less well studied. Here, spectroscopic relaxometry measurements of 31 human cortical bone specimens provided a more detailed picture of of both bound and pore water. The results included mean, standard deviation, and range of spectra from both bound and pore water, as well as novel presentations of the 2D distribution of pore water. Importantly, for each sample the pore water spectrum was found to span more than one order of magnitude and varied substantially across the 31 sample studies. Because many existing methods assume pore water to be mono-exponential and constant across individuals, the results were used to compute the potential effect neglecting this intra- and intersample variation on accurate MRI measurement of both bound and pore water concentrations. The greatest effect was found for adiabatic inversion recovery (AIR) based measurements of bound water concentration, which showed an average of 8.8% and as much as 37% error when using a common mono-exponential assumption of pore water . Despite these errors, the simulated AIR measurements were still moderately well correlated with the bound water concentrations derived from the spectroscopic data.

4D flow MRI in abdominal vessels: prospective comparison of k-t accelerated free breathing acquisition to standard respiratory navigator gated acquisition

Volumetric phase-contrast magnetic resonance imaging with three-dimensional velocity encoding (4D flow MRI) has shown utility as a non-invasive tool to examine altered blood flow in chronic liver disease. Novel 4D flow MRI pulse sequences with spatio-temporal acceleration can mitigate the long acquisition times of standard 4D flow MRI, which are an impediment to clinical adoption. The purpose of our study was to demonstrate feasibility of a free-breathing, spatio-temporal (k−t) accelerated 4D flow MRI acquisition for flow quantification in abdominal vessels and to compare its image quality, flow quantification and inter-observer reproducibility with a standard respiratory navigator-gated 4D flow MRI acquisition. Ten prospectively enrolled patients (M/F: 7/3, mean age = 58y) with suspected portal hypertension underwent both 4D flow MRI acquisitions. The k−t accelerated acquisition was approximately three times faster (3:11 min ± 0:12 min/9:17 min ± 1:41 min, p < 0.001) than the standard respiratory-triggered acquisition. Vessel identification agreement was substantial between acquisitions and observers. Average flow had substantial inter-sequence agreement in the portal vein and aorta (CV < 15%) and poorer agreement in hepatic and splenic arteries (CV = 11–38%). The k−t accelerated acquisition recorded reduced velocities in small arteries and reduced splenic vein flow. Respiratory gating combined with increased acceleration and spatial resolution are needed to improve flow measurements in these vessels.

Skull phantom-based methodology to validate MRI co-registration accuracy for Gamma Knife radiosurgery.

Target localization, for stereotactic radiosurgery (SRS) treatment with Gamma Knife, has become increasingly reliant on the co-registration between the planning MRI and the stereotactic cone-beam computed tomography (CBCT). Validating image registration between modalities would be particularly beneficial when considering the emergence of novel functional and metabolic MRI pulse sequences for target delineation. This study aimed to develop a phantom-based methodology to quantitatively compare the co-registration accuracy of the standard clinical imaging protocol to a representative MRI sequence that was likely to fail co-registration. The comparative methodology presented in this study may serve as a useful tool to evaluate the clinical translatability of novel MRI sequences. A realistic human skull phantom with fiducial marker columns was designed and manufactured to fit into a typical MRI head coil and the Gamma Knife patient positioning system. A series of "optimized" 3D MRI sequences-T1 -weighted Dixon, T1 -weighted fast field echo (FFE), and T2 -weighted fluid-attenuated inversion recovery (FLAIR)-were acquired and co-registered to the CBCT. The same sequences were "compromised" by reconstructing without geometric distortion correction and re-collecting with lower signal-to-noise-ratio (SNR) to simulate a novel MRI sequence with poor co-registration accuracy. Image similarity metrics-structural similarity (SSIM) index, mean squared error (MSE), and peak SNR (PSNR)-were used to quantitatively compare the co-registration of the optimized and compromised MR images. The ground truth fiducial positions were compared to positions measured from each optimized image volume revealing a maximum median geometric uncertainty of 0.39mm (LR), 0.92mm (AP), and 0.13mm (SI) between the CT and CBCT, 0.60mm (LR), 0.36mm (AP), and 0.07mm (SI) between the CT and T1 -weighted Dixon, 0.42mm (LR), 0.23mm (AP), and 0.08mm (SI) between the CT and T1 -weighted FFE, and 0.45mm (LR), 0.19mm (AP), and 1.04mm (SI) between the CT and T2 -weighted FLAIR. Qualitatively, pairs of optimized and compromised image slices were compared using a fusion image where separable colors were used to differentiate between images. Quantitatively, MSE was the most predictive and SSIM the second most predictive metric for evaluating co-registration similarity. A clinically relevant threshold of MSE, SSIM, and/or PSNR may be defined beyond which point an MRI sequence should be rejected for target delineation based on its dissimilarity to an optimized sequence co-registration. All dissimilarity thresholds calculated using correlation coefficients with in-plane geometric uncertainty would need to be defined on a sequence-by-sequence basis and validated with patient data. This study utilized a realistic skull phantom and image similarity metrics to develop a methodology capable of quantitatively assessing whether a modern research-based MRI sequence can be co-registered to the Gamma Knife CBCT with equal or less than equal accuracy when compared to a clinically accepted protocol.

MRI Diagnosis of Clival Cancer and Sixth Nerve Palsy.

Imaging diagnosis of clival cancer may be difficult, in part because of normal variation in marrow signal with aging. Identifying whether clival cancer has damaged the sixth cranial nerve is a further challenge because minimal clival abnormalities could impinge on the nerve, which travels very close to the clivus. Two neuroradiologists, who were unaware of previous imaging and clinical diagnoses, reviewed MRI studies of 25 patients with cancer but no clival involvement and no sixth nerve palsy, 24 patients with clival cancer but without sixth nerve palsy, and 31 patients with clival cancer and sixth nerve palsy. The radiologists were tasked with determining whether there was clival cancer, whether there was a sixth nerve palsy and its laterality, and with indicating the pulse sequences used to make those determinations. Both neuroradiologists correctly identified all 25 cases with a normal clivus. In about half of those cases, they depended on finding a homogeneously bright marrow signal; in the remaining cases, they excluded cancer by determining that the clivus was not expanded and that there were no focal signal abnormalities. Both neuroradiologists correctly identified clival cancer in 54 (98%) of the 55 cases with and without sixth nerve palsy. In doing so, they relied mostly on clival expansion but also on focal signal abnormalities. Both neuroradiologists were at least 80% correct in identifying a sixth nerve palsy, but they often incorrectly identified a palsy in patients who did not have one. When there was a one-sided signal abnormality or the clivus was expanded in one direction, both neuroradiologists were accurate in identifying the side of the sixth nerve palsy. Current MRI pulse sequences allow accurate differentiation of a normal from a cancerous clivus. When the marrow signal is not homogeneously bright in adults, cancer can be diagnosed on the basis of clival expansion or focal signal abnormalities. MRI is less accurate in predicting the presence of a sixth nerve palsy. However, the side of a unilateral palsy can be predicted when the clivus is clearly expanded in one direction or there is a focal signal abnormality on one side.

Evaluating the Quality of Optimal MRCP Image Using RT-2D-Compressed SENSE(CS)Turbo Spin Echo: Comparing Respiratory Triggering(RT)-2D-SENSE Turbo Spin Echo and Breath Hold-2D-Single-Shot Turbo Spin Echo.

This study aimed to select the pulse sequence providing the optimal MRCP image quality by applying various reduction and denoising level parameters—which could improve image quality and shorten examination time—to BH-2D-SSh TSE, RT- 2D-SENSE TSE, and RT-2D-Compressed SENSE(CS) TSE and then comparing and analyzing the obtained images. This study was carried out using 30 subjects (15 men and 15 women with a mean age of 53 ± 8.76 years) who underwent an MRCP test using 3.0T MRI equipment. These 30 subjects were composed of 20 patients (CHDD: 7; LC: 6; and IPMN: 7) and 10 volunteers without a disease. When the CS technique was used, five reduction values (1.1, 1.2, 1.3, 1.4, and 1.5) were used and four denoising levels (No, Weak, Medium, and Strong) were used. The existing SENSE method was based on a reduction value of 1, and other parameters were set the same. The image data of BH-2D-SSh TSE, RT-2D-SENSE TSE, and RT-CS-2D TSE used for the analysis were acquired in the coronal plane, and the acquired data underwent MIP post-processing for analysis. To compare these techniques, SNR and CNR were measured for six biliary duct images for the purpose of quantitative analysis, and qualitative analysis was performed on the sharpness of the duct, the overall quality of the image, and the motion artifact. The results of the quantitative and standard analyses showed that the RT-2D-CS TSE technique had the highest results for all IPMN, LC, and CHDD diseases (p < 0.05). Moreover, SNR and CNR were the highest when the reduction value was set to 1.3 and the denoising level was set to medium as the CS setting values (p < 0.05). Compared with the conventional RT-2D-SENSE TSE, the test time decreased by 20% and SNR and CNR increased by 14% on average. When conducting RT-2D-CS TSE, we found that it shortened the examination time and improved the image quality compared to the existing RT-2D-SENSE TSE. Unlike previous studies, this study using the RT technique shows that it is a useful MRI Pulse Sequence technique able to replace the BH-2D-SSh TSE and BH-3D-SENSE GRASE techniques, which require the patient to hold their breath during the test.

Dual-Echo magnetic resonance imaging pulse sequence in diagnosis of temporomandibular disorders

Objective: This study was conducted to assess the diagnostic accuracy of different MRI pulse sequence dual-echo-PD in the diagnosis of temporomandibular disorders. Subjects and methods: Twenty seven patients (54 Temporomandibular joints) with painful joints or limited mouth opening or unexplained longstanding headache were enrolled in the study to examine the diagnostic accuracy of magnetic resonance imaging sequence dual-echo in delineation of the articular disc position, the disc morphology, and the cortical bone in comparison to the gold standard of MRI scanning sequence: proton density weighted images. Results: Dual-echo-PD weighted image showed 94.7% sensitivity and 96.3% diagnostic accuracy in identifying articular disc position. Dual-echo-PD showed no statistically significant difference than proton-density in delineation of disc morphology or cortical bone. Conclusions: The dual-echo imaging sequence can be used instead of using PD to delineate disc position, morphology, and cortical bone.

Review and consensus recommendations on clinical APT-weighted imaging approaches at 3T: Application to brain tumors.

Amide proton transfer‐weighted (APTw) MR imaging shows promise as a biomarker of brain tumor status. Currently used APTw MRI pulse sequences and protocols vary substantially among different institutes, and there are no agreed‐on standards in the imaging community. Therefore, the results acquired from different research centers are difficult to compare, which hampers uniform clinical application and interpretation. This paper reviews current clinical APTw imaging approaches and provides a rationale for optimized APTw brain tumor imaging at 3 T, including specific recommendations for pulse sequences, acquisition protocols, and data processing methods. We expect that these consensus recommendations will become the first broadly accepted guidelines for APTw imaging of brain tumors on 3 T MRI systems from different vendors. This will allow more medical centers to use the same or comparable APTw MRI techniques for the detection, characterization, and monitoring of brain tumors, enabling multi‐center trials in larger patient cohorts and, ultimately, routine clinical use.

Multiparametric quantitative renal MRI in children and young adults: comparison between healthy individuals and patients with chronic kidney disease

Multiparametric quantitative renal MRI may provide noninvasive radiologic biomarkers of chronic kidney disease (CKD) based on investigations in animal models and adults. We aimed to (1) obtain normative multiparametric quantitative MRI data from the kidneys of healthy children and young adults, (2) compare MRI measurements between healthy control participants and patients with CKD, and (3) determine if MRI measurements correlate with clinical and laboratory data as well as histology. This was a prospective, case-control study of 20 healthy controls and 12 CKD patients who underwent percutaneous renal biopsy ranging from 12 to 23years of age between October 2018 and March 2020. Kidney function was documented and pathology assessed for fibrosis/inflammation. Utilizing a field strength of 1.5T, we examined renal T1, T2, and T2* relaxation mapping, MR elastography (MRE), and diffusion-weighted imaging (DWI). A single analyst made all manual measurements for quantitative MRI pulse sequences. Independent measurements from cortex, medulla, and whole kidney were obtained by drawing regions of interest on single slices from the upper, mid, and lower kidney. A weighted average was calculated for each kidney; if two kidneys, the right and left were averaged. Continuous variables were compared with Mann-Whitney U test; bivariate relationships were assessed using Spearman rank-order correlation. Median estimated glomerular filtration rate (eGFR) was 112.3ml/min/1.73 m2 in controls (n = 20, 10 females) and 55.0ml/min/m2 in CKD patients (n = 12, 2 females) (p < 0.0001). Whole kidney (1333 vs. 1291ms; p = 0.018) and cortical (1212 vs 1137ms; p < 0.0001) T1 values were higher in CKD patients. Cortical T1 values correlated with eGFR (rho = -0.62; p = 0.0003) and cystatin C (rho = 0.58; p = 0.0007). Whole kidney (1.87 vs. 2.02 10-3 mm2/s; p = 0.007), cortical (1.89 vs. 2.04 10-3 mm2/s; p = 0.008), and medullary (1.87 vs. 1.98 10-3 mm2/s; p = 0.0095) DWI apparent diffusion coefficients (ADC) were lower in CKD patients. Whole kidney ADC correlated with eGFR (rho = 0.45; p = 0.012) and cystatin C (rho = -0.46; p = 0.009). Cortical histologic inflammation correlated with DWI ADC (rho = -0.71; p = 0.011). Renal T1 relaxation and DWI ADC measurements differ between pediatric healthy controls and CKD patients, correlate with laboratory markers of CKD, and may have histologic correlates.

A multi-modality medical imaging head and neck phantom: Part 1. Design and fabrication

A novel anthropomorphic head and neck phantom which features the emulation of blood flow and perfusion is proposed. The phantom is helpful in both education and research and contains major blood vessels and a porous silicone elastomer brain compartment with microvascular capillary flow. The porous brain compartment is fabricated by use of a novel cast-moulding-dissolution technique. The skull and vertebra are fabricated by a combination of 3D printing and cast-moulding and are tissue equivalent with CT numbers ranging from 1000 HU to 1200 HU. The elastic structure of the phantom allows ultrasound imaging in the neck region. MRI compatible pressure sensors measure the pressure in the carotic arteries and the jugular veins and pulsatile flow is created by use of a peristaltic pump. The pressure-flow dynamics are physiologically realistic and also matches well with computational simulations of porous Darcy flow. The phantom can be used to optimize and validate MRI pulse sequences and protocols for flow imaging, MR angiography, Arterial Spin Labeling (ASL) and dynamic contrast enhanced (DCE) MRI.

Macromolecular Proton Fraction as a Myelin Biomarker: Principles, Validation, and Applications.

Macromolecular proton fraction (MPF) is a quantitative MRI parameter describing the magnetization transfer (MT) effect and defined as a relative amount of protons bound to biological macromolecules with restricted molecular motion, which participate in magnetic cross-relaxation with water protons. MPF attracted significant interest during past decade as a biomarker of myelin. The purpose of this mini review is to provide a brief but comprehensive summary of MPF mapping methods, histological validation studies, and MPF applications in neuroscience. Technically, MPF maps can be obtained using a variety of quantitative MT methods. Some of them enable clinically reasonable scan time and resolution. Recent studies demonstrated the feasibility of MPF mapping using standard clinical MRI pulse sequences, thus substantially enhancing the method availability. A number of studies in animal models demonstrated strong correlations between MPF and histological markers of myelin with a minor influence of potential confounders. Histological studies validated the capability of MPF to monitor both demyelination and re-myelination. Clinical applications of MPF have been mainly focused on multiple sclerosis where this method provided new insights into both white and gray matter pathology. Besides, several studies used MPF to investigate myelin role in other neurological and psychiatric conditions. Another promising area of MPF applications is the brain development studies. MPF demonstrated the capabilities to quantitatively characterize the earliest stage of myelination during prenatal brain maturation and protracted myelin development in adolescence. In summary, MPF mapping provides a technically mature and comprehensively validated myelin imaging technology for various preclinical and clinical neuroscience applications.

Phantom Construction and Equipment Configurations for Characterizing Electrical Properties Using MRI.

Phantom objects are commonly employed in MRI systems as stable substitutes for biological tissues to ensure systems for measuring images are operating correctly and safely. For magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance electrical property tomography (MREPT), conductivity or permittivity phantoms play an important role in checking MRI pulse sequences, MREIT equipment performance, and algorithm validation. The construction of these phantoms is explained in this chapter. In the first part, materials used for phantom construction are introduced. Ingredients for modifying the electromagnetic properties and relaxation times are presented, and the advantages and disadvantages of aqueous, gel, and hybrid conductivity phantoms are explained. The devices and methods used to confirm phantom electromagnetic properties are explained. Next, different types of MREIT electrode materials and the constant current sources used for MREIT studies are discussed. In the last section, we present the results of previous MREIT and MREPT studies.

The neuroradiology of progressive multifocal leukoencephalopathy: a clinical trial perspective.

Progressive multifocal leukoencephalopathy (PML) is an opportunistic infection of the CNS caused by the JC virus, which infects white and grey matter cells and leads to irreversible demyelination and neuroaxonal damage. Brain MRI, in addition to the clinical presentation and demonstration of JC virus DNA either in the CSF or by histopathology, is an important tool in the detection of PML. In clinical practice, standard MRI pulse sequences are utilized for screening, diagnosis and monitoring of PML, but validated imaging-based outcome measures for use in prospective, interventional clinical trials for PML have yet to be established. We review the existing literature regarding the use of MRI and PET in PML and discuss the implications of PML histopathology for neuroradiology. MRI not only demonstrates the localization and extent of PML lesions, but also mirrors the tissue destruction, ongoing viral spread, and resulting inflammation. Finally, we explore the potential for imaging measures to serve as an outcome in PML clinical trials and provide recommendations for current and future imaging outcome measure development in this area.

NIMG-44. PROGNOSTIC VALUE OF PH- AND OXYGEN-SENSITIVE MRI IN GLIOMA PATIENTS

Abstract Hypoxia and tissue acidosis are two key features of the glioma microenvironment, both associated with a more aggressive phenotype through promotion of invasion, angiogenesis, and resistance to a vast number of therapies. In the current study, we demonstrate that higher levels of acidity and hypoxia in glioma are associated with worse prognosis by using simultaneous pH- and oxygen-sensitive amine chemical exchange saturation transfer spin-and-gradient echo echo-planar imaging (CEST-SAGE-EPI). A total of 159 histologically confirmed adult glioma patients (WHO grade II: N = 42; grade III: N = 38; grade IV, N = 79) were retrospectively evaluated. All patients were scanned with a custom amine CEST-SAGE-EPI MRI pulse sequence at 3T. Magnetization transfer ratio asymmetry (MTRasym) at 3ppm was used as a measure of relative acidity, R2’ was used as a surrogate of hypoxia, and their product MTRasym×R2' was used to quantify the degree of both acidity and hypoxia. Cox regression was performed to evaluate prognostic factors for OS and PFS. Univariate results suggested higher hypoxia, R2' (HR = 1.44, p = 0.0002), and higher combined measure of acidity and hypoxia, MTRasym×R2' (HR = 1.14, p = 0.0008), were associated with a shorter OS. When considering age, treatment status, and IDH mutation status as covariates, R2' and MTRasym×R2' remained significantly associated with patient OS (R2': HR = 1.27, p = 0.045; MTRasym×R2': HR = 1.17, p = 0.002). Within the treatment naïve patients, tumor acidity MTRasym, was also associated with OS (HR = 3.72, p = 0.003). R2' and MTRasym×R2' were significantly associated with PFS, both using univariate (R2': p &amp;lt; 0.0001; MTRasym×R2': p &amp;lt; 0.0001) and multivariate analyses including clinical factors (R2': p = 0.010; MTRasym×R2': p &amp;lt; 0.0001). In summary, tumor acidity and hypoxia measured using pH- and oxygen-sensitive metabolic MRI are significant prognostic factors in glioma.

Body Interventional MRI for Diagnostic and Interventional Radiologists: Current Practice and Future Prospects.

Clinical use of MRI for guidance during interventional procedures emerged shortly after the introduction of clinical diagnostic MRI in the late 1980s. However, early applications of interventional MRI (iMRI) were limited owing to the lack of dedicated iMRI magnets, pulse sequences, and equipment. During the 3 decades that followed, technologic advancements in iMRI magnets that balance bore access and field strength, combined with the development of rapid MRI pulse sequences, surface coils, and commercially available MR-conditional devices, led to the rapid expansion of clinical iMRI applications, particularly in the field of body iMRI. iMRI offers several advantages, including superior soft-tissue resolution, ease of multiplanar imaging, lack of ionizing radiation, and capability to re-image the same section. Disadvantages include longer examination times, lack of MR-conditional equipment, less operator familiarity, and increased cost. Nonetheless, MRI guidance is particularly advantageous when the disease is best visualized with MRI and/or when superior soft-tissue contrast is needed for treatment monitoring. Safety in the iMRI environment is paramount and requires close collaboration among interventional radiologists, MR physicists, and all other iMRI team members. The implementation of risk-limiting measures for personnel and equipment in MR zones III and IV is key. Various commercially available MR-conditional needles, wires, and biopsy and ablation devices are now available throughout the world, depending on the local regulatory status. As such, there has been tremendous growth in the clinical applications of body iMRI, including localization of difficult lesions, biopsy, sclerotherapy, and cryoablation and thermal ablation of malignant and nonmalignant soft-tissue neoplasms. Online supplemental material is available for this article. ©RSNA, 2021.

PD36-01 CORRELATION BETWEEN WHITE MATTER INTEGRITY AND LOWER URINARY TRACT SYMPTOMS (LUTS) IN FEMALE MULTIPLE SCLEROSIS PATIENTS

You have accessJournal of UrologyUrodynamics/Lower Urinary Tract Dysfunction/Female Pelvic Medicine: Neurogenic Voiding Dysfunction (PD36)1 Sep 2021PD36-01 CORRELATION BETWEEN WHITE MATTER INTEGRITY AND LOWER URINARY TRACT SYMPTOMS (LUTS) IN FEMALE MULTIPLE SCLEROSIS PATIENTS Darshil Choksi, Khue Tran, Bradley Schott, Christof Karmonik, Timonthy Boone, and Rose Khavari Darshil ChoksiDarshil Choksi More articles by this author , Khue TranKhue Tran More articles by this author , Bradley SchottBradley Schott More articles by this author , Christof KarmonikChristof Karmonik More articles by this author , Timonthy BooneTimonthy Boone More articles by this author , and Rose KhavariRose Khavari More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002040.01AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Multiple Sclerosis (MS) is a demyelinating disease of the central nervous system and around 90% of MS patients experience LUTS. The degree of demyelination and signal disruption can be quantified by measuring the functional anisotropy (FA) and mean diffusivity (MD) of white matter tracts (WMTs) via diffusion tensor imaging (DTI). In this study, we analyzed the correlation between clinical variables evaluating LUTS (including urodynamics parameters and validated questionnaires) with both FA and MD values in a cohort of female MS patients. METHODS: Twenty-eight MS women with LUTS were enrolled in this prospective study. Urodynamics and validated questionnaires including the Urinary Distress Inventory (UDI-6) and Incontinence Impact Questionnaire (IIQ-7) were collected. DTI images were acquired (32 directions, one B0 image) for each subject using the standard MRI pulse sequence available on the Philips 3 Tesla Ingenia scanner. The AFNI software package was used to automatically align clinical DTI images onto the ICMB DTI81 atlas to extract the FA and MD values of 50 tracts for each subject. Pearson’s correlation was performed between FA and MD values versus each clinical variable for all 50 tracts. Any WMTs with a p-value less than 0.05 on the Pearson’s correlation with FA or MD in at least one of the clinical variables was considered a statistically significant correlation. A positive correlation coefficient (R) for MD and negative correlation for FA were noted as signs of WMT demyelination contributing directly to clinical symptoms whereas a negative correlation for MD and positive correlation for FA were noted to indicate compensatory strengthening of the WMT in an effort to maintain continence in the presence of MS. Only WMTs with |R| >0.3 were reported. RESULTS: Five WMTs (ML-L, CP-R, SS-R, UNC-L, and SFO-R) showed statistically significant demyelination in correlation to symptoms, whereas three WMTs (IFO-R, PCR-R, and CGH-L) displayed statistically significant compensatory strengthening (Table 1). CONCLUSIONS: The ability to correlate changes in WMT signaling to clinical symptoms strengthens our understanding of the demyelination that leads to LUTS in female MS patients and can enable the development of targeted therapies for patients early in the disease course. Source of Funding: Dr. Khavari reports that she is partially supported by K23DK118209, National Institute of Health, NIDDK (RK). Also supported by Houston Methodist Clinician Scientist Award (RK) © 2021 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 206Issue Supplement 3September 2021Page: e595-e595 Advertisement Copyright & Permissions© 2021 by American Urological Association Education and Research, Inc.MetricsAuthor Information Darshil Choksi More articles by this author Khue Tran More articles by this author Bradley Schott More articles by this author Christof Karmonik More articles by this author Timonthy Boone More articles by this author Rose Khavari More articles by this author Expand All Advertisement Loading ...