Dynamic MRI Techniques Research Articles

Application of Differential Subsampling with Cartesian Ordering in Evaluating Left Ovarian Venous Reflux for Pretreatment Planning for Pelvic Venous Disorders.

The diagnosis of a common cause of chronic pelvic pain can be made by visualizing reflux in the ovarian veins. Fluoroscopic venography is the gold standard for diagnosing ovarian vein reflux, but it is an invasive technique that exposes patients to ionizing radiation. MRI, with its lack of ionizing radiation and capability of high-temporal and spatial-resolution vascular imaging, has the potential to provide similar diagnostic information. This retrospective report describes and assesses the utility of a dynamic contrast-enhanced MRI technique based on Differential Subsampling with Cartesian Ordering (DISCO)-MRI in 30 patients with chronic pelvic pain. Among the 14 patients who underwent both DISCO-MRI and fluoroscopic venograms, 11 (78.6%) exhibited concordant results, while 3 patients (21.4%) had discordant findings. These results suggest the potential of multiphasic contrast-enhanced DISCO-MRI as a non-invasive diagnostic tool for evaluating chronic pelvic pain.

Dynamic contrast-enhanced mammography and breast MRI in the diagnosis of breast cancer and detection of tumor size.

The aim of this study is to evaluate the performance of contrast-enhanced mammography (CEM) and dynamic breast MRI techniques for diagnosing breast lesions, assess the diagnostic accuracy of CEM's using histopathological findings, and compare lesion size measurements obtained from both methods with pathological size. This prospective study included 120 lesions, of which 70 were malignant, in 104 patients who underwent CEM and MRI within a week. Two radiologists independently evaluated the MR and CEM images in separate sessions, using the BI-RADS classification system. Additionally, the maximum sizes of lesion were measured. Diagnostic accuracy parameters and the receiver operating characteristics (ROC) curves were constructed for the two modalities. The correlation between the maximum diameter of breast lesions observed in MRI, CEM, and pathology was analyzed. The overall diagnostic values for MRI were as follows: sensitivity 97.1%, specificity 60%, positive predictive value (PPV) 77.3%, negative predictive value (NPV) 93.8%, and accuracy 81.7%. Correspondingly, for CEM, the sensitivity, accuracy, specificity, PPV, and NPV were 97.14%, 81.67%, 60%, 77.27%, and 93.75%, respectively. The ROC analysis of CEM revealed an area under the curve (AUC) of 0.907 for observer 1 and 0.857 for observer 2, whereas MRI exhibited an AUC of 0.910 for observer 1 and 0.914 for observer 2. Notably, CEM showed the highest correlation with pathological lesion size (r = 0.660 for observer 1 and r = 0.693 for observer 2, p < 0.001 for both). CEM can be used with high sensitivity and similar diagnostic performance comparable to MRI for diagnosing breast cancer. CEM proves to be a successful diagnostic method for precisely determining tumor size.

“The Pituitary within GRASP” – Golden-Angle Radial Sparse Parallel Dynamic MRI Technique and Applications to the Pituitary Gland

MRI is the preferred radiologic modality for evaluating the pituitary gland. An important component of pituitary MRI examinations is dynamic contrast-enhanced MRI. Compared to conventional dynamic techniques, golden-angle radial sparse parallel (GRASP) imaging offers multiple advantages, including the ability to achieve higher spatial and temporal resolution. In this narrative review, we discuss dynamic imaging of the pituitary gland, the technical fundamentals of GRASP, and applications of GRASP to the pituitary gland.

The Role of MRI in the Diagnosis of Pelvic Floor Disorders.

This article provides an overview of MRI as a dynamic imaging modality as well as recent updates on the role of MRI in the evaluation of female pelvic floor disorders, including pelvic organ prolapse (POP), rectal prolapse, and defecatory dysfunction. Pelvic floor disorders in women are common, and demand for treatment is high. Recently, multidisciplinary guidelines for dynamic MRI have been published to reflect this need. Despite criticisms that MRI is an expensive modality, cost-analysis studies are demonstrating utility for MRI in surgical decision-making trees for patients at risk for treatment failure after POP repairs. Novel measures such as anterior pelvic area and levator volumes are being used to predict and study patients with and at risk for POP. Recent standardized radiographic guidelines as reviewed in this paper will likely lead to improved reproducibility of dynamic MRI techniques across institutions, making complex pelvic floor assessment increasingly accessible to patients while creating opportunities for novel and collaborative research.

Monitoring of Breast Lesions after Breast Conservative Therapy: Does A Combination of Dynamic and Functional MRI Techniques Can Add Value in Early Detection of Recurrent Malignancy?

Abstract Background: To assess efficacy of combined dynamic and functional MRI techniques in early detection of recurrent malignancy after breast conservative therapy and differentiating it from other post-operative lesions. Aim of Study: To assess efficacy of combined dynamic and functional MRI techniques in early detection of recurrent malignancy after breast conservative therapy and differentiating it from other post-operative lesions. Patients and Methods: Thirty female patients who under-went breast conservative therapy were involved in this pro-spective study. Patients were examined by sono-mammography that aroused suspicious of breast lesions followed by DCE-MRI & DWI-MRI to exclude recurrence. DWI was performed using b-values of 50, 400, 800s/mm2. All patients were subjected to histopathological confirmation which was the gold standard in this study. Results: Eight patients had pathologically proven recur-rence and 22 patients showed spectrum of post-operative changes. DCE- MRI diagnosis (considering lesion morphology, enhancement pattern) overestimated 2 lesions were scored BIRADS 4 and proved pathologically as fat necrosis. When adding the data elicited by the DWI to the DCE-MRI assessment, the statistical analysis presented 100% sensitivity, 95.4% specificity, 88.9% PPV, 100% NPV and 96.6% accuracy. Conclusion: Combination of functional & dynamic MRI techniques added high significant value in follow-up of breast lesion occurred after BCT as it can avoid biopsy in positive patients, to send negative patients to follow-up and reserving biopsy in the cases with a clinico-radiological mismatch. Breast MRI should be the imaging modality of choice in detection of the tumoral recurrence, and differentiating it from other post-operative lesions.

The value of dynamic subtraction MRI technique in the assessment of treatment response of hepatocellular carcinoma to transcatheter arterial chemoembolization

BackgroundHepatocellular carcinoma is considered to be the fifth most common cancer worldwide. Resection and liver transplantation have a high survival in the correct clinical scenarios; however, locoregional therapy has many advantages over tumor resection like preservation of hepatic parenchyma and overall less morbidity and mortality. Our aim was to present the role of dynamic subtraction MRI technique in the assessment of treatment response of hepatocellular carcinoma to transarterial chemoembolization.MethodsThe study consisted of 43 patients with 55 hepatocellular carcinoma lesions who underwent transarterial chemoembolization procedure and followed up by dynamic MRI of the liver with post processing to obtain subtraction images 1–1.5 months after the procedure. If no signs of disease activity, another follow up study was preformed 2–4 months later. Five patients were excluded due to misregistration artifact at the subtraction images. The final cohort is 38 patients having 50 lesions. Precontrast T1, T2, dynamic contrast enhanced, and diffusion-weighted images were acquired. Subtracted dynamic images were created on the workstation. Sequences were assessed by three experienced readers in hepatic imaging. The sensitivity, specificity, positive predictive value, negative predictive value, 95% confidence interval, and overall agreement were calculated for the dynamic and subtracted dynamic images.ResultsThe subtraction images have sensitivity of 96%, specificity of 100%, PPV of 100%, and NPV of 100% Compared to 96%, 100%, 100%, 96%, and 96%, 100%, 100% 96% for the three readers respectively. On the other hand, the dynamic images has sensitivity of 92%, specificity of 96%, PPV of 95%, and NPV of 92.3% compared to 92%, 96%, 95%, 92.3% and 80%, 68%, 71.4%, and 77.2% for the three readers respectively.ConclusionSubtraction technique is a useful confirmative tool as it had higher sensitivity, specificity, PPV, and NPV values compared to the dynamic and diffusion images with high level of agreement between the readers and also associated with significantly higher reader confidence levels.

Role of Magnetic Resonance Spectroscopic Imaging in Recategorization of BIRADS 4 Breast Lesions

AbstractBackground: Breast cancer is one of the major causes of death among females, its early diagnosis allow better prognosis and prolonged survival rates of the patients. Post contrast dynamic MRI is the most sensitive method for breast cancer detection which has also good diagnostic performance for evaluation of different breast pathological lesions. Magnetic Resonance (MR) spectroscopy is a functional MRI technique which is used to study the metabolic profile of different breast lesions to improve the diagnostic accuracy of MRI especially in BIRADS 4 breast lesions in order to reduce the unnecessary biopsies.Aim of Study: Evaluation of the role of multi-voxel MR spectroscopy in the recategorization of BIRADS 4 breast lesions when combined with Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI).Material and Methods: This study included 63 patients, their ages ranged from 28 to 73 years old with mean age 46.7 years old. All the patients included in this study were subjected to history, clinical examination, MRI examination and his-topathology. Initially the included breast lesions were catego-rized as BIRADS 4 by conventional post contrast dynamic MRI techniques, and then we added the results of the magnetic resonance spectroscopic imaging to detect whether the spec-troscopic data can improve the diagnostic accuracy of the MRI study. Finally the reported diagnosis was confirmed by histopathological specimens obtained after excision biopsy and core needle biopsy. We used 1.5 T MRI system and the sequences performed included T1 & T2 pulse sequences, STIR and dynamic contrast enhanced MRI followed by MRS for the suspected lesions. For statistical analysis we used T-test and ROC curve.Results: This study included 63 female patients, their ages ranged from 28 to 73 years old with mean age 46.7 years old. All the breast lesion were categorized as BI-RADS 4 breast lesions based on the Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) then after magnetic resonance spectroscopy the breast lesions were re-categorized into BIRADS 3, 4 and 5 categories. Finally the results were compared to the histopathological results. The most common clinical presentation is palpable mass. We had 33 pathologically proven benign lesions and 30 pathologically proven malignant lesions. The diagnosis was downgraded into BIRADS 3 in 29 cases and upgraded into BIRADS 5 in 28 cases and in 6 cases there was no change in the BIRADS 4 categorization after MRS. During MRS examination the choline resonance peak was detected at a frequency of 3.23ppm, and the choline SNR was measured at cut off value of 2. There were statistically significant differences between malignant and benign breast lesions, the choline SNR measured 6.31±0.99 (mean ± SD) in the malignant lesions and it measured 1.902±0.47 (mean ± SD) in the benign lesions. The sensitivity, specificity, PPV, NPV and accuracy measured 81.3%, 62.6%, 76.5%, 67.1% and 73.4% for the DCE-MRI and measured 87.9%, 89.1%, 85.2%, 88.9% and 94.8% for combined assessment by MRS and DCE-MRI.Conclusion: Magnetic resonance spectroscopic imaging can be problem solving method for BIRADS 4 breast lesions when combined with dynamic contrast enhanced MRI to improve its diagnostic accuracy.

GRASP-Pro: imProving GRASP DCE-MRI through self-calibrating subspace-modeling and contrast phase automation.

To propose a highly accelerated, high-resolution dynamic contrast-enhanced MRI (DCE-MRI) technique called GRASP-Pro (golden-angle radial sparse parallel imaging with imProved performance) through a joint sparsity and self-calibrating subspace constraint with automated selection of contrast phases. GRASP-Pro reconstruction enforces a combination of an explicit low-rank subspace-constraint and a temporal sparsity constraint. The temporal basis used to construct the subspace is learned from an intermediate reconstruction step using the low-resolution portion of radial k-space, which eliminates the need for generating the basis using auxiliary data or a physical signal model. A convolutional neural network was trained to generate the contrast enhancement curve in the artery, from which clinically relevant contrast phases are automatically selected for evaluation. The performance of GRASP-Pro was demonstrated for high spatiotemporal resolution DCE-MRI of the prostate and was compared against standard GRASP in terms of overall image quality, image sharpness, and residual streaks and/or noise level. Compared to GRASP, GRASP-Pro reconstructed dynamic images with enhanced sharpness, less residual streaks and/or noise, and finer delineation of the prostate without prolonging reconstruction time. The image quality improvement reached statistical significance (P < 0.05) in all the assessment categories. The neural network successfully generated contrast enhancement curves in the artery, and corresponding peak enhancement indexes correlated well with that from the manual selection. GRASP-Pro is a promising method for rapid and continuous DCE-MRI. It enables superior reconstruction performance over standard GRASP and allows reliable generation of artery enhancement curve to guide the selection of desired contrast phases for improving the efficiency of GRASP MRI workflow.

Impaired brain glymphatic flow in experimental hepatic encephalopathy

Background & AimsNeuronal function is exquisitely sensitive to alterations in the extracellular environment. In patients with hepatic encephalopathy (HE), accumulation of metabolic waste products and noxious substances in the interstitial fluid of the brain is thought to result from liver disease and may contribute to neuronal dysfunction and cognitive impairment. This study was designed to test the hypothesis that the accumulation of these substances, such as bile acids, may result from reduced clearance from the brain.MethodsIn a rat model of chronic liver disease with minimal HE (the bile duct ligation [BDL] model), we used emerging dynamic contrast-enhanced MRI and mass-spectroscopy techniques to assess the efficacy of the glymphatic system, which facilitates clearance of solutes from the brain. Immunofluorescence of aquaporin-4 (AQP4) and behavioural experiments were also performed.ResultsWe identified discrete brain regions (olfactory bulb, prefrontal cortex and hippocampus) of altered glymphatic clearance in BDL rats, which aligned with cognitive/behavioural deficits. Reduced AQP4 expression was observed in the olfactory bulb and prefrontal cortex in HE, which could contribute to the pathophysiological mechanisms underlying the impairment in glymphatic function in BDL rats.ConclusionsThis study provides the first experimental evidence of impaired glymphatic flow in HE, potentially mediated by decreased AQP4 expression in the affected regions.Lay summaryThe ‘glymphatic system’ is a newly discovered brain-wide pathway that facilitates clearance of various substances that accumulate in the brain due to its activity. This study evaluated whether the function of this system is altered in a model of brain dysfunction that occurs in cirrhosis. For the first time, we identified that the clearance of substances from the brain in cirrhosis is reduced because this clearance system is defective. This study proposes a new mechanism of brain dysfunction in patients with cirrhosis and provides new targets for therapy.

The Role of Diffusion Weighted Magnetic Resonance Imaging and Subtraction Magnetic Resonance imaging in Assessing Treatment Response of Hepatocellular Carcinoma After Transarterial Chemoembolization

Background: Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and has a poor prognosis unless treated. Ablative therapies are promising treatment options for patients who are not eligible for surgery. Monitoring tumor response after transarterial chemoemolization (TACE) procedure is an important task in oncologic imaging. Early favorable response indicates effectiveness of therapy, while early treatment failure identification is also critical in patient management. In such cases further re-treatment will be mandatory. Aim of work: The aim of this study is to evaluate the efficiency of both diffusion weighted images and subtracted dynamic MRI technique in the detection of residual/ recurrent disease after TACE ablation of non resectable hepatocellular carcinoma (HCC) lesions. Accurate judgment of tumor viability will help diagnose the need for further treatment sessions. Patients and Methods: This study included 32 patients having 54 HCC lesions that underwent transarterial chemoembolization procedure over a period of 6 months (2017- 2018) were followed up 1-1.5 months by dynamic MRI. 12 patients of which underwent a second follow up within 3-4 months. Patients’ ages ranged between 59 to 73 years (mean age 53.1); 26 patients were males and 6 were females. All patients had liver cirrhosis related to chronic viral hepatitis. Results: In 1ry response and follow up findings post TACE, where good response was defied as disappearance of any intra tumoral arterial enhancement in treated lesions, residual disease was defined as at least 30% reduction in the sum of diameters of the viable enhancing lesion in the arterial phase, no response was less than 30% reduction in the enhancing lesion diameters. Progressive disease was defined as 20% increase in the sum of diameters of the enhancing lesions in comparison to the target lesion diameter at the start of treatment. Conclusion: MRI is a powerful tool in detection of residual tumor viability, quantifying tumor necrosis and detecting complications after TACE. Imaging protocol should include dynamic study combined with post processing subtraction images for better tissue characterization.

Dynamic MRI to quantify musculoskeletal motion: A systematic review of concurrent validity and reliability, and perspectives for evaluation of musculoskeletal disorders.

PurposeTo report evidence for the concurrent validity and reliability of dynamic MRI techniques to evaluate in vivo joint and muscle mechanics, and to propose recommendations for their use in the assessment of normal and impaired musculoskeletal function.Materials and methodsThe search was conducted on articles published in Web of science, PubMed, Scopus, Academic search Premier, and Cochrane Library between 1990 and August 2017. Studies that reported the concurrent validity and/or reliability of dynamic MRI techniques for in vivo evaluation of joint or muscle mechanics were included after assessment by two independent reviewers. Selected articles were assessed using an adapted quality assessment tool and a data extraction process. Results for concurrent validity and reliability were categorized as poor, moderate, or excellent.ResultsTwenty articles fulfilled the inclusion criteria with a mean quality assessment score of 66% (±10.4%). Concurrent validity and/or reliability of eight dynamic MRI techniques were reported, with the knee being the most evaluated joint (seven studies). Moderate to excellent concurrent validity and reliability were reported for seven out of eight dynamic MRI techniques. Cine phase contrast and real-time MRI appeared to be the most valid and reliable techniques to evaluate joint motion, and spin tag for muscle motion.ConclusionDynamic MRI techniques are promising for the in vivo evaluation of musculoskeletal mechanics; however results should be evaluated with caution since validity and reliability have not been determined for all joints and muscles, nor for many pathological conditions.

Optimization of Quantitative Dynamic Postgadolinium MRI Technique Using Normalized Ratios for the Evaluation of Temporomandibular Joint Synovitis in Patients with Juvenile Idiopathic Arthritis.

MR imaging has been shown to be useful in the diagnosis of juvenile idiopathic arthritis of the temporomandibular joint. Prior MR imaging approaches have relied mainly on the subjective interpretation of synovial enhancement as a marker for synovial inflammation. Although, more recently, several attempts have been made to quantify synovial enhancement, these methods have not taken into account the dynamic enhancement characteristics of the temporomandibular joint and the effect of sampling time. Our aim was to develop a clinically feasible, reproducible, dynamic, contrast-enhanced MR imaging technique for the quantitative assessment of temporomandibular joint synovitis in patients with juvenile idiopathic arthritis and to study the effect of sampling time on the evaluation of synovitis. This was a retrospective study of all patients who had dynamic, contrast-enhanced coronal T1 3T MR imaging through the temporomandibular joint at our institution between January 1, 2015, and July 8, 2016. Patients in this cohort included those with a history of juvenile idiopathic arthritis and control patients who underwent MR imaging for other routine, clinical purposes. Synovial enhancement was calculated for each temporomandibular joint using 3 different types of equations termed normalization ratios. The enhancement profiles generated by each equation were studied to determine which provided the best discrimination between affected and unaffected joints, was the least susceptible to sampling errors, and was the most clinically feasible. A ratio of synovial enhancement (defined as the difference between the postgadolinium and the pregadolinium T1 signal of the synovium) to the postgadolinium signal of the longus capitis provided the best discrimination between affected and unaffected joints, the least susceptibility to sampling error, and was thought to be the most clinically feasible method of quantification of synovial inflammation. Additional synovial enhancement ratios studied did not provide the same level rates of discrimination between the affected and unaffected joints and were thought to be too temporally variable to provide reliable clinical use. We provide a robust, reproducible, dynamic gadolinium-enhanced MR imaging technique for the quantitative assessment of temporomandibular joint synovitis in patients with juvenile idiopathic arthritis.

Quantifying musculoskeletal motion using dynamic MRI techniques: A systematic review of validity and perspectives for musculoskeletal disorder evaluation

This systematic review reports the evidence of validity and reliability of dynamic MRI (dMRI) techniques in quantifying in vivo skeletal joint movement (kinematics) or muscle tracking and to propose recommendations of use for the assessment of normal and impaired musculoskeletal function. A systematic search was conducted on six bibliographic databases (Web of science, PubMed, Scopus, Academic search Premier, Pascal, and Cochrane Library) for articles published between 1990 and January 2017. Prospective studies that reported the concurrent validity and/or reliability of determining in vivo skeletal joint or muscle motion using dMRI techniques were included after assessment by two independent reviewers for inclusion and exclusion criteria. Selected articles were assessed using an adapted quality assessment tool and a data extraction process. Concurrent validity and reliability measurement results were categorized as poor, moderate, or excellent for this review. Bibliographic search identified 20 articles that met the inclusion and exclusion criteria. The mean quality assessment score for all the selected articles was 66% (±10.4). Concurrent validity and/or reliability of eight dMRI techniques evaluating the musculoskeletal motion were reported. Selected studies spanned various joints and muscles with knee joint being the most evaluated joint (seven studies), followed by ankle and temporomandibular joint (two studies each). Moderate to excellent concurrent validity and reliability were reported for most of the dMRI techniques. Based on the current level of metrological evidence Cine Phase-Contrast and Real-time MRI techniques stand out for determining skeletal joint motion whereas Spin tag MRI technique stands out for determining muscle motion. dMRI techniques can be effectively applied to understand in vivo skeletal joint and muscle movement mechanics for both healthy and pathological populations. However, caution must be exercised as the evidence of validity and reliability of using these techniques in all the skeletal joints and muscles have not been systematically evaluated. Furthermore, clinical utility of the techniques in impaired population is not addressed yet in terms of concurrent validity and reliability measures setting up a good research direction for future studies. Examples of the best available techniques and outcomes for rehabilitation application will be provided during the presentation.

Magnetic resonance imaging of head and neck vascular anomalies

Purpose: The aim of this study was to describe typical MRI features of the head and neck vascular anomalies and the possible diagnostic pitfalls. Patients and methods: Patients with extracranial vascular anomalies of the head and neck, who underwent MRI examinations between January 2013 and January 2016, were included in the study. Precontrast and postcontrast T1-WI,T2-WI, with and without fat saturation were acquired. When indicated, a noncontrast MR angiography was performed. Dynamic postcontrast MRI techniques were available in six children. Results: The study included 33 patients (age ranged from 10 to 20 years, mean: 49 months). MRI confirmed the clinical diagnosis in equivocal cases, and provided proper determination of lesion extension and/or associated intracranial anomalies. The study included 10 cases of vascular tumors (hemangioma), whereas the remaining 23 cases had the diagnosis of vascular malformations (one patient with arteriovenous malformation, one with capillary malformation, seven with venous, nine with macrocystic lymphatic, and five with microcystic lymphatic malformations). Conclusion: Vascular anomalies in the head and neck are mostly diagnosed on clinical basis; however, when the history is uncertain or the diagnosis is equivocal, a well-tailored MR examination can be a single valuable diagnostic tool providing structural and functional information. Keywords: children, head and neck, hemangioma, lymphatic malformation, magnetic resonance angiography, venous malformation

A continuous-infusion dynamic MRI model at 3.0 Tesla for the serial quantitative evaluation of microvascular proliferation in an animal model of glioblastoma multiforme.

To develop a continuous-infusion dynamic MRI technique to characterize tumor-associated microvascular proliferation (MVP) in a rat brain model of glioblastoma multiforme. The proposed model assumes effects due to tumor-associated MVP (eg, vascular permeability, Ktrans ; intravascular plasma fraction, vp ) cannot be individually separated and solves for a single parameter (kvasc ) that quantifies the T1 -weighted contrast enhancement from dynamic images acquired during continuous contrast agent (CA) infusion. Untreated C6 tumor-bearing animals (N = 6) were serially imaged on postoperative days (PODs) 14 and 18 with a 3 Tesla clinical scanner utilizing a dynamic spatial and temporal resolution of 0.38 × 0.38 × 1.5 mm3 and 3.47 s, respectively. An association was present between PODs 14 and 18 for median tumor kvasc (Pearson's r = 0.94, P = 0.0052) and CA concentration ([CA], derived from pre- and postcontrast R1 maps; r = 0.94, P = 0.0054). On POD 18, there was a voxel-based association between kvasc and [CA] within each tumor (0.45 < r < 0.82, P < 0.001). However, voxel-based subregions demonstrated a reduced association between kvasc and [CA] (N = 5; -0.08 < r < 0.22, P > 0.05) or an inverse association (N = 1; r = -0.28, P = 0.001), indicating differences between locations of vascular permeability and subsequent CA pooling in tumors. The continuous-infusion method may provide a quantitative measure for characterizing and monitoring tumor-associated MVP. Magn Reson Med 78:1824-1838, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Pulmonary perfusion quantification with flow-sensitive inversion recovery (FAIR) UTE MRI in small animal imaging.

Blood perfusion in lung parenchyma is an important property for assessing lung function. In small animals, its quantitation is limited even with radioactive isotopes or dynamic contrast-enhanced MRI techniques. In this study, the feasibility flow-sensitive alternating inversion recovery (FAIR) for the quantification of blood flow in lung parenchyma in free breathing rats at 7T has been investigated. In order to obtain sufficient signal from the short T2 * lung parenchyma, a 2D ultra-short echo time (UTE) Look-Locker read-out has been implemented. Acquisitions were segmented to maintain acquisition time within an acceptable range. A method to perform retrospective respiratory gating (DC-SG) has been applied to investigate the impact of respiratory movement. Reproducibilities within and between sessions were estimated, and the ability of FAIR-UTE to identify the decrease of lung perfusion under hyperoxic conditions was tested. The implemented technique allowed for the visualization of lung parenchyma with excellent SNR and no respiratory artifact even in ungated acquisitions. Lung parenchyma perfusion was obtained as 32.54±2.26mL/g/min in the left lung, and 34.09±2.75mL/g/min in the right lung. Application of retrospective gating significantly but minimally changes the perfusion values, implying that respiratory gating may not be necessary with this center-our acquisition method. A decrease of 10% in lung perfusion was found between normoxic and hyperoxic conditions, proving the feasibility of the FAIR-UTE approach to quantify lung perfusion changes.

Dynamic Contrast-Enhanced CT and MRI for Pulmonary Nodule Assessment

The purpose of this article is to review advanced imaging of pulmonary nodules, including pathologic and pharmacokinetic background, conventional contrast-enhanced CT and MRI assessment, dynamic contrast-enhanced CT and MRI techniques, and dual-source and area-detector CT systems for pulmonary nodule evaluation. Clinicians need to understand the underlying principles and pathologic and pharmacokinetic backgrounds of contrast-enhanced CT and MRI to further improve diagnostic performance. With adjustments in image acquisition and postprocessing, contrast-enhanced CT and MRI, especially the dynamic versions, can have enhanced clinical application for pulmonary nodules and expanded clinical relevance for other thoracic diseases.

Golden‐angle radial sparse parallel MRI: Combination of compressed sensing, parallel imaging, and golden‐angle radial sampling for fast and flexible dynamic volumetric MRI

To develop a fast and flexible free-breathing dynamic volumetric MRI technique, iterative Golden-angle RAdial Sparse Parallel MRI (iGRASP), that combines compressed sensing, parallel imaging, and golden-angle radial sampling. Radial k-space data are acquired continuously using the golden-angle scheme and sorted into time series by grouping an arbitrary number of consecutive spokes into temporal frames. An iterative reconstruction procedure is then performed on the undersampled time series where joint multicoil sparsity is enforced by applying a total-variation constraint along the temporal dimension. Required coil-sensitivity profiles are obtained from the time-averaged data. iGRASP achieved higher acceleration capability than either parallel imaging or coil-by-coil compressed sensing alone. It enabled dynamic volumetric imaging with high spatial and temporal resolution for various clinical applications, including free-breathing dynamic contrast-enhanced imaging in the abdomen of both adult and pediatric patients, and in the breast and neck of adult patients. The high performance and flexibility provided by iGRASP can improve clinical studies that require robustness to motion and simultaneous high spatial and temporal resolution. Magn Reson Med 72:707-717, 2014. © 2013 Wiley Periodicals, Inc.

Dynamic Contrast-Enhanced MRI Evaluation of Cerebral Cavernous Malformations

The aim of this study is to quantitatively evaluate the behavior of CNS cavernous malformations (CCMs) using a dynamic contrast-enhanced MRI (DCEMRI) technique sensitive for slow transfer rates of gadolinium. The prospective study was approved by the institutional review board and was HIPPA compliant. Written informed consent was obtained from 14 subjects with familial CCMs (4 men and 10 women, ages 22-76years, mean 48.1years). Following routine anatomic MRI of the brain, DCEMRI was performed for six slices, using T1 mapping with partial inversion recovery (TAPIR) to calculate T1 values, following administration of 0.025mmol/kg gadolinium DTPA. The transfer rate (Ki) was calculated using the Patlak model, and Ki within CCMs was compared to normal-appearing white matter as well as to 17 normal control subjects previously studied. All subjects had typical MRI appearance of CCMs. Thirty-nine CCMs were studied using DCEMRI. Ki was low or normal in 12 lesions and elevated from 1.4 to 12 times higher than background in the remaining 27 lesions. Ki ranged from 2.1E-6 to 9.63E-4min(-1), mean 3.55E-4. Normal-appearing white matter in the CCM patients had a mean Ki of 1.57E-4, not statistically different from mean WM Ki of 1.47E-4 in controls. TAPIR-based DCEMRI technique permits quantifiable assessment of CCMs in vivo and reveals considerable differences not seen with conventional MRI. Potential applications include correlation with biologic behavior such as lesion growth or hemorrage, and measurement of drug effects.

Prostate Cancer: Comparison of Dynamic Contrast-Enhanced MRI Techniques for Localization of Peripheral Zone Tumor

The objective of this study was to compare the performance of different methodologies for interpretation of dynamic contrast-enhanced MRI (DCE-MRI) in localization of peripheral zone prostate cancer. Forty-three men (mean age, 59±8 years) with biopsy-proven prostate cancer who underwent prostate MRI including DCE-MRI before prostatectomy were included. Two observers independently reviewed DCE-MRI data using three methodologies: qualitative, in which kinetic curves of signal intensity versus time were generated for foci showing rapid enhancement on subtracted contrast-enhanced images; semiquantitative, in which a biexponential heuristic model was used to generate color-coded maps depicting maximum slope and washout of contrast enhancement; and quantitative, in which a Tofts model was used to generate color-coded influx rate transfer constant (Ktrans) and efflux rate transfer constant (Kep) maps. Findings were stratified by whether suspicious foci showed evidence of washout with each method and compared with histopathologic results in each sextant. There was similar accuracy for the semiquantitative and quantitative models for both observers irrespective of requiring evidence of washout. For the more experienced observer, requiring washout resulted in lower sensitivity and higher specificity for the qualitative and semiquantitative models. Also for the more experienced observer, use of either a semiquantitative or quantitative model provided greater sensitivity compared with a qualitative model when requiring washout. There was no association between tumor detection and Gleason score for any DCE-MRI methodology for either reader. For the experienced reader, sensitivity for peripheral zone tumor was increased by use of either a semiquantitative or quantitative model compared with a qualitative model and decreased by requiring washout. We failed to identify a difference in performance between semiquantitative and quantitative models.