Performance of a fast and high-resolution multi-echo spin-echo sequence for prostate T2 mapping across multiple systems.

PURPOSE: To evaluate the performance of a multi-echo spin-echo sequence with k-t undersampling scheme (k-t T2 ) in prostate cancer. METHODS: Phantom experiments were performed at five systems to estimate the bias, short-term repeatability, and reproducibility across all systems expressed with the within-subject coefficient of variation (wCV). Monthly measurements were performed on two systems for long-term repeatability estimation. To evaluate clinical repeatability, two T2 maps (voxel size 0.8 × 0.8 × 3 mm3 ; 5 min) were acquired at separate visits on one system for 13 prostate cancer patients. Repeatability was assessed per patient in relation to spatial resolution. T2 values were compared for tumor, peripheral zone, and transition zone. RESULTS: Phantom measurements showed a small bias (median = -0.9 ms) and good short-term repeatability (median wCV = 0.5%). Long-term repeatability was 0.9 and 1.1% and reproducibility between systems was 1.7%. The median bias observed in patients was -1.1 ms. At voxel level, the median wCV was 15%, dropping to 4% for structures of 0.5 cm3 . The median tumor T2 values (79 ms) were significantly lower (P < 0.001) than in the peripheral zone (149 ms), but overlapped with the transition zone (91 ms). CONCLUSIONS: Reproducible T2 mapping of the prostate is feasible with good spatial resolution in a clinically reasonable scan time, allowing reliable measurement of T2 in structures as small as 0.5 cm3 . Magn Reson Med 79:1586-1594, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Optimal high b-value for diffusion weighted MRI in diagnosing high risk prostate cancers in the peripheral zone.

PURPOSE: To retrospectively determine the optimal b-value(s) of diffusion-weighted imaging (DWI) associated with intermediate-high risk cancer in the peripheral zone (PZ) of the prostate. MATERIALS AND METHODS: Forty-two consecutive patients underwent multi b-value (16 evenly spaced b-values between 0 and 2000 s/mm2 ) DWI along with multi-parametric MRI (MP-MRI) of the prostate at 3 Tesla followed by trans-rectal ultrasound/MRI fusion guided targeted biopsy of suspicious lesions detected at MP-MRI. Computed DWI images up to a simulated b-value of 4000 s/mm2 were also obtained using a pair of b-values (b = 133 and 400 or 667 or 933 s/mm2 ) from the multi b-value DWI. The contrast ratio of average intensity of the targeted lesions and the background PZ was determined. Receiver operator characteristic curves and the area under the curve (AUCs) were obtained for separating patients eligible for active surveillance with low risk prostate cancers from intermediate-high risk prostate cancers as per the cancer of the prostate risk assessment (CAPRA) scoring system. RESULTS: The AUC first increased then decreased with the increase in b-values reaching maximum at b = 1600 s/mm2 (0.74) with no statistically significant different AUC of DWI with b-values 1067-2000 s/mm2 . The AUC of computed DWI increased then decreased with the increase in b-values reaching a maximum of 0.75 around b = 2000 s/mm2 . There was no statistically significant difference between the AUC of optimal acquired DWI and either of optimal computed DWI. CONCLUSION: The optimal b-value for acquired DWI in differentiating intermediate-high from low risk prostate cancers in the PZ is b = 1600 s/mm2 . The computed DWI has similar performance as that of acquired DWI with the optimal performance around b = 2000 s/mm2 . LEVEL OF EVIDENCE: 4 J. Magn. Reson. Imaging 2017;45:125-131.

Application of an unsupervised multi-characteristic framework for intermediate-high risk prostate cancer localization using diffusion-weighted MRI.

PURPOSE: The aim of this proof-of-concept work is to propose an unsupervised framework that combines multiple parameters, in "positive-if-all-positive" manner, from different models to localize tumors. METHODS: A voxel-by-voxel analysis of the DW-MRI images of whole prostate was performed to obtain parametric maps for D*, D, f, and K using the IVIM and kurtosis models. Ten patients with moderate or high-risk prostate cancer were included in study. The mean age and serum PSA for these 10 patients were 65years (range 54-78) and 21.9ng/mL (range 4.84-44.81), respectively. These patients were scanned using a DW spin-echo sequence with echo-planar readout with 16 equidistantly spaced b-values in the range of 0-2000s/mm2 (TE=58ms; TR=3990ms; spatial resolution 2.19×2.19×2.73mm3, slices =26, FOV=140×140mm, slice gap =0.27mm, NSA=2). RESULTS: The proposed framework detected 24 lesions of which 14 were true positive with 58% tumor detection rate on lesion-based analysis with sensitivity of 100%. The mpMRI evaluation (PIRADSv2) identified 12 of 14 true positive lesions with sensitivity of 86%; positive predictive value of mpMRI was 92%. The index lesions were visible on all framework maps and were coded as the most suspicious in 9 of 10 patients. CONCLUSION: Preliminary results of the proposed framework indicate high patient-based sensitivity with 100% detection rate for identifying moderate-high risk aggressive index lesions.

A Phase I Dosing Study of Ferumoxytol for MR Lymphography at 3 T in Patients With Prostate Cancer.

OBJECTIVE: The objective of our study was to determine the optimal dose of ferumoxytol for performing MR lymphography (MRL) at 3 T in patients with prostate cancer. SUBJECTS AND METHODS: This phase I trial enrolled patients undergoing radical prostatectomy (RP) with bilateral pelvic lymph node dissection (PLND). Three groups of five patients each (total of 15 patients) received IV ferumoxytol before RP with bilateral PLND at each of the following doses of iron: 4, 6, and 7.5 mg Fe/kg. Patients underwent abdominopelvic MRI at 3 T before and 24 hours after ferumoxytol injection using T2- and T2*-weighted sequences. Normalized signal intensity (SI) and normalized SD changes from baseline to 24 hours after injection within visible lymph nodes were calculated for each dose level. Linear mixed effects models were used to estimate the effects of dose on the percentage SI change and log-transformed SD change within visible lymph nodes to determine the optimal dose of ferumoxytol for achieving uniform low SI in normal nodes. RESULTS: One patient who was excluded from the study group had a mild allergic reaction requiring treatment after approximately 2.5 mg Fe/kg ferumoxytol injection whereupon the injection was interrupted. The 15 study group patients tolerated ferumoxytol at all dose levels. The mean percentage SI change in 13 patients with no evidence of lymph metastasis was -36.4%, -45.4%, and -65.1% for 4, 6, and 7.5 mg Fe/kg doses, respectively (p = 0.041). CONCLUSION: A dose level of 7.5 mg Fe/kg ferumoxytol was safe and effective in deenhancing benign lymph nodes. This dose therefore can be the starting point for future phase II studies regarding the efficacy of ferumoxytol for MRL.

Magnetic resonance sentinel lymph node imaging of the prostate with gadofosveset trisodium-albumin: preliminary results in a canine model.

RATIONALE AND OBJECTIVES: To determine if intraprostatic injection of gadofosveset trisodium mixed with human serum albumin (HSA) can identify sentinel lymph nodes (LNs) draining the prostate on magnetic resonance imaging (MRI) in a canine model. MATERIALS AND METHODS: Three male canines weighing between 25.7 and 41.3 kg were anesthetized, placed in a 3-T MRI, and a needle was placed transrectally into one side of the prostate using a commercially available intrarectal needle guide. Gadofosveset trisodium premixed with 10% HSA was then administered at doses ranging from 0.1 to 2.5 mL. T1W MRI was performed immediately after injection, and two readers evaluated images for visualization of LNs draining the prostate. RESULTS: Intraprostatic injection of 0.2 mL gadofosveset trisodium premixed with HSA identified the draining periprostatic LNs in all cases. Delayed images demonstrated upper echelon nodes in the pelvis and the abdomen. Higher volume injections resulted in excessive periprostatic extravasation, whereas lower volume injections resulted in suboptimal visualization of LNs. CONCLUSIONS: We demonstrate that gadofosveset trisodium (premixed with 10% HSA) injected intraprostatically at 0.2 mL visualized LNs draining the prostate. This approach can be readily adapted for clinical applications such as sentinel LN imaging in prostate cancer patients before surgery.

Comparison of calculated and acquired high b value diffusion-weighted imaging in prostate cancer.

PURPOSE: To determine whether the performance of calculated high b value diffusion-weighted images (DWI) derived from regular lower b value DWI using exponential diffusion decay models (intravoxel incoherent motion = IVIM and diffusional kurtosis = DK) is comparable to acquired high b value DWI in prostate cancer detection. MATERIALS AND METHODS: One hundred six patients underwent diagnostic multiparametric prostate MRI at 3T using an endorectal coil. Five b value (b = 0, 188, 375, 563, 750 s/mm(2)) DWI and high b value (b = 0, 1000 and 2000 s/mm(2)) DWI were acquired. Calculated high b value (b = 1000 s/mm(2) and b = 2000 s/mm(2)) DWI were derived from the DWI dataset using DK and IVIM models. Calculated and acquired high b value DWI images were compared for lesion visibility and image quality by two experienced radiologists (1 and 6 years of experience). GEE with Wald test was used to compare the image quality among the four calculated high b value DWI by comparing the proportion of lesions in each model which were comparable to the acquired images. This comparison was done for all lesions and by lesion location (PZ or CG; low apical/anterior or apical/mid/base) RESULTS: More lesions were visible on acquired b = 2000 s/mm(2) compared to b = 1000 s/mm(2) DWI. Calculated high b value DWI using the IVIM model had approximately the same number of lesions as acquired high b value DWI, whereas the DK model had fewer lesions than acquired images. The image quality of calculated high b value DWI was comparable to that of acquired images, and the highest quality images were obtained with b1000IVIM. The image quality of calculated b1000IVIM was the same as that of acquired DWI in apical/mid/base (98%) locations and comparable in low apical and anterior (95.4%) locations. The image quality of calculated b2000IVIM was inferior in both apical/mid/base (86.2%) locations and comparable in low apical and anterior (83.9%) locations. CONCLUSION: Calculated high b value DWI obtained using IVIM model has same lesion visibility as that of acquired DWI. The image quality of calculated high b value DWI relative to corresponding acquired DWI decreases with increase in b value.

Whole prostate volume and shape changes with the use of an inflatable and flexible endorectal coil.

Purpose. To determine to what extent an inflatable endorectal coil (ERC) affects whole prostate (WP) volume and shape during prostate MRI. Materials and Methods. 79 consecutive patients underwent T2W MRI at 3T first with a 6-channel surface coil and then with the combination of a 16-channel surface coil and ERC in the same imaging session. WP volume was assessed by manually contouring the prostate in each T2W axial slice. PSA density was also calculated. The maximum anterior-posterior (AP), left-right (LR), and craniocaudal (CC) prostate dimensions were measured. Changes in WP prostate volume, PSA density, and prostate dimensions were then evaluated. Results. In 79 patients, use of an ERC yielded no significant change in whole prostate volume (0.6 ± 5.7%, P = 0.270) and PSA density (-0.2 ± 5.6%, P = 0.768). However, use of an ERC significantly decreased the AP dimension of the prostate by -8.6 ± 7.8% (P < 0.001), increased LR dimension by 4.5 ± 5.8% (P < 0.001), and increased the CC dimension by 8.8 ± 6.9% (P < 0.001). Conclusion. Use of an ERC in prostate MRI results in the shape deformation of the prostate gland with no significant change in the volume of the prostate measured on T2W MRI. Therefore, WP volumes calculated on ERC MRI can be reliably used in clinical workflow.

Atlas based AAM and SVM model for fully automatic MRI prostate segmentation.

Automatic prostate segmentation in MR images is a challenging task due to inter-patient prostate shape and texture variability, and the lack of a clear prostate boundary. We propose a supervised learning framework that combines the atlas based AAM and SVM model to achieve a relatively high segmentation result of the prostate boundary. The performance of the segmentation is evaluated with cross validation on 40 MR image datasets, yielding an average segmentation accuracy near 90%.

Functional and molecular imaging of localized and recurrent prostate cancer.

Prostate cancer is the most common malignancy among American men. Imaging of localized and recurrent prostate cancer is challenging since conventional imaging techniques are limited. New imaging techniques such as multiparametric MRI and PET with targeted tracers have been investigated extensively in the last decade. As a result, the role of novel imaging techniques for the detection of localized and recurrent prostate cancer has recently expanded. In this review, novel functional and molecular imaging techniques used in the management of localized and recurrent prostate cancer are discussed.

Three-dimensional regional strain analysis in porcine myocardial infarction: a 3T magnetic resonance tagging study.

BACKGROUND: Previous studies of mechanical strain anomalies in myocardial infarction (MI) have been largely limited to analysis of one-dimensional (1D) and two-dimensional (2D) strain parameters. Advances in cardiovascular magnetic resonance (CMR) methods now permit a complete three-dimensional (3D) interrogation of myocardial regional strain. The aim of this study was to investigate the incremental value of CMR-based 3D strain and to test the hypothesis that 3D strain is superior to 1D or 2D strain analysis in the assessment of viability using a porcine model of infarction. METHODS: Infarction was induced surgically in 20 farm pigs. Cine, late gadolinium enhancement, and CMR tagging images were acquired at 11 days before (baseline), and 11 days (early) and 1 month (late) after induction of infarct. Harmonic phase analysis was performed to measure circumferential, longitudinal, and radial strains in myocardial segments, which were defined based on the transmurality of delayed enhancement. Univariate, bivariate, and multivariate logistic regression models of strain parameters were created and analyzed to compare the overall diagnostic accuracy of 3D strain analysis with 1D and 2D analyses in identifying the infarct and its adjacent regions from healthy myocardium. RESULTS: 3D strain differed significantly in infarct, adjacent, and remote segments (p<0.05) at early and late post-MI. In univariate, bivariate, and multivariate analyses, circumferential, longitudinal, and radial strains were significant factors (p<0.001) in differentiation of infarct and adjacent segments from baseline values. In identification of adjacent segments, receiver operating characteristic analysis using the 3D strain multivariate model demonstrated a significant improvement (p<0.01) in overall diagnostic accuracy in comparison with 2D (circumferential and radial) and 1D (circumferential) models (3D: 96%, 2D: 81%, and 1D: 71%). A similar trend was observed in identification of infarct segments. CONCLUSIONS: Cumulative 3D strain information accurately identifies infarcts and their neighboring regions from healthy myocardium. The 3D interrogation of myocardial contractility provides incremental diagnostic accuracy in delineating the dysfunctional and nonviable myocardium in comparison with 1D or 2D quantification of strain. The infarct neighboring regions are the major beneficiaries of the 3D assessment of regional strain.

Regional coronary endothelial function is closely related to local early coronary atherosclerosis in patients with mild coronary artery disease: pilot study.

BACKGROUND: Coronary endothelial function is abnormal in patients with established coronary artery disease and was recently shown by MRI to relate to the severity of luminal stenosis. Recent advances in MRI now allow the noninvasive assessment of both anatomic and functional (endothelial function) changes that previously required invasive studies. We tested the hypothesis that abnormal coronary endothelial function is related to measures of early atherosclerosis such as increased coronary wall thickness. METHODS AND RESULTS: Seventeen arteries in 14 healthy adults and 17 arteries in 14 patients with nonobstructive coronary artery disease were studied. To measure endothelial function, coronary MRI was performed before and during isometric handgrip exercise, an endothelial-dependent stressor, and changes in coronary cross-sectional area and flow were measured. Black blood imaging was performed to quantify coronary wall thickness and indices of arterial remodeling. The mean stress-induced change in cross-sectional area was significantly higher in healthy adults (13.5%±12.8%, mean±SD, n=17) than in those with mildly diseased arteries (-2.2%±6.8%, P<0.0001, n=17). Mean coronary wall thickness was lower in healthy subjects (0.9±0.2 mm) than in patients with coronary artery disease (1.4±0.3 mm, P<0.0001). In contrast to healthy subjects, stress-induced changes in cross-sectional area, a measure of coronary endothelial function, correlated inversely with coronary wall thickness in patients with coronary artery disease (r=-0.73, P=0.0008). CONCLUSIONS: There is an inverse relationship between coronary endothelial function and local coronary wall thickness in patients with coronary artery disease but not in healthy adults. These findings demonstrate that local endothelial-dependent functional changes are related to the extent of early anatomic atherosclerosis in mildly diseased arteries. This combined MRI approach enables the anatomic and functional investigation of early coronary disease.

A statistical model-based technique for accounting for prostate gland deformation in endorectal coil-based MR imaging.

In prostate brachytherapy procedures, combining high-resolution endorectal coil (ERC)-MRI with Computed Tomography (CT) images has shown to improve the diagnostic specificity for malignant tumors. Despite such advantage, there exists a major complication in fusion of the two imaging modalities due to the deformation of the prostate shape in ERC-MRI. Conventionally, nonlinear deformable registration techniques have been utilized to account for such deformation. In this work, we present a model-based technique for accounting for the deformation of the prostate gland in ERC-MR imaging, in which a unique deformation vector is estimated for every point within the prostate gland. Modes of deformation for every point in the prostate are statistically identified using a set of MR-based training set (with and without ERC-MRI). Deformation of the prostate from a deformed (ERC-MRI) to a non-deformed state in a different modality (CT) is then realized by first calculating partial deformation information for a limited number of points (such as surface points or anatomical landmarks) and then utilizing the calculated deformation from a subset of the points to determine the coefficient values for the modes of deformations provided by the statistical deformation model. Using a leave-one-out cross-validation, our results demonstrated a mean estimation error of 1mm for a MR-to-MR registration.

Total removal of unwanted harmonic peaks (TruHARP) MRI for single breath-hold high-resolution myocardial motion and strain quantification.

Current MRI methods for myocardial motion and strain quantification have limited resolution because of Fourier space spectral peak interference. Methods have been proposed to remove this interference in order to improve resolution; however, these methods are clinically impractical due to the prolonged imaging times. In this paper, we propose total removal of unwanted harmonic peaks (TruHARP); a myocardial motion and strain quantification methodology that uses a novel single breath-hold MR image acquisition protocol. In post-processing, TruHARP separates the spectral peaks in the acquired images, enabling high-resolution motion and strain quantification. The impact of high resolution on calculated circumferential and radial strains is studied using realistic Monte Carlo simulations, and the improvement in strain maps is demonstrated in six human subjects.

IDENTIFICATION OF MYOCARDIAL INFARCTION USING THREE-DIMENSIONAL STRAIN TENSOR FRACTIONAL ANISOTROPY.

Accurate localization of myocardial viability is important in diagnosis of infarction. Regional strain function provides excessive information for clinical decision making but comparison of strain tensor profiles across differing tissue types is usually difficult due to multivariate nature of tensors. It is desirable to describe tensors with simplified scalar indices which are more mathematically and statistically intuitive. In this work, anisotropy of tensors in healthy and experimental infarct regions in a large animal model is assessed and compared to directional components of strain tensors which are currently the most popular indices in active use. Myocardial strain tensors are computed using zHARP, a magnetic resonance (MR) tagging technique that provides quantification of cardiac function with direct computation of three-dimensional tensors from two-dimensional short axis MR images. Fractional anisotropy of strain tensors shows high correlation with late gadolinium enhanced images and is capable of discrimination between healthy and infarcted regions.

TRUHARP: SINGLE BREATH-HOLD MRI FOR HIGH RESOLUTION CARDIAC MOTION AND STRAIN QUANTIFICATION.

MRI techniques for tissue motion and strain quantifications have limited resolution because of interference from the conjugate echo or spectral peak in Fourier space. Methods have been proposed to remove this interference in order to improve resolution; however, these methods are clinically impractical due to long image acquisition time. In this paper, we propose TruHARP, an MRI motion and strain quantification methodology that involves a novel single breath-hold imaging protocol. In post-processing, TruHARP separates the spectral peaks in the acquired datasets, enabling high resolution motion and strain quantification. The impact of high resolution on circumferential and radial strain is studied using a realistic simulation and the improvement in strain maps is demonstrated in an in-vivo human study.