Fast Spin-echo MR Research Articles

High-Resolution Single-Shot Fast Spin-Echo MR Imaging with Deep Learning Reconstruction Algorithm Can Improve Repeatability and Reproducibility of Follicle Counting.

To investigate the diagnostic performance of high-resolution single-shot fast spin-echo (SSFSE) imaging with deep learning (DL) reconstruction algorithm on follicle counting and compare it with original SSFSE images and conventional fast spin-echo (FSE) images. This study included 20 participants (40 ovaries) with clinically confirmed polycystic ovary syndrome (PCOS) who underwent high-resolution ovary MRI, including three-plane T2-weighted FSE sequences and slice-matched T2-weighted SSFSE sequences. A DL reconstruction algorithm was applied to the SSFSE sequences to generate SSFSE-DL images, and the original SSFSE images were also saved. Subjective evaluations such as the blurring artifacts, subjective noise, and clarity of the follicles on the SSFSE-DL, SSFSE, and conventional FSE images were independently conducted by two observers. Intra-class correlation coefficients and Bland-Altman plots were used to present the repeatability and reproducibility of the follicle number per ovary (FNPO) based on the three types of images. SSFSE-DL images showed less blurring artifact, subjective noise, and better clarity of the follicles than SSFSE and FSE (p < 0.05). For the repeatability of the FNPO, SSFSE-DL showed the highest intra-observer (ICC = 0.930; 95% CI: 0.878-0.962) and inter-observer (ICC = 0.914; 95% CI: 0.843-0.953) agreements. The inter-observer 95% limits of agreement (LOA) for SSFSE-DL, SSFSE, and FSE ranged from -3.7 to 4.5, -4.4 to 7.0, and -7.1 to 7.6, respectively. The intra-observer 95% LOA for SSFSE-DL, SSFSE, and FSE ranged from -3.5 to 4.0, -5.1 to 6.1, and -5.7 to 4.2, respectively. The absolute values of intra-observer and inter-observer differences for SSFSE-DL were significantly lower than those for SSFSE and FSE (p < 0.05). Compared with the original SSFSE images and the conventional FSE images, high-resolution SSFSE images with DL reconstruction algorithm can better display follicles, thus improving FNPO assessment.

DeepLiverNet: a deep transfer learning model for classifying liver stiffness using clinical and T2-weighted magnetic resonance imaging data in children and young adults.

Although MR elastography allows for quantitative evaluation of liver stiffness to assess chronic liver diseases, it has associated drawbacks related to additional scanning time, patient discomfort, and added costs. To develop a machine learning model that can categorically classify the severity of liver stiffness using both anatomical T2-weighted MRI and clinical data for children and young adults with known or suspected pediatric chronic liver diseases. We included 273 subjects with known or suspected chronic liver disease. We extracted data including axial T2-weighted fast spin-echo fat-suppressed images, clinical data (e.g., demographic/anthropomorphic data, particular medical diagnoses, laboratory values) and MR elastography liver stiffness measurements. We propose DeepLiverNet (a deep transfer learning model) to classify patients into one of two groups: no/mild liver stiffening (<3kPa) or moderate/severe liver stiffening (≥3kPa). We conducted internal cross-validation using 178 subjects, and external validation using an independent cohort of 95 subjects. We assessed diagnostic performance using accuracy, sensitivity, specificity and area under the receiver operating characteristic curve (AuROC). In the internal cross-validation experiment, the combination of clinical and imaging data produced the best performance (AuROC=0.86) compared to clinical (AuROC=0.83) or imaging (AuROC=0.80) data alone. Using both clinical and imaging data, the DeepLiverNet correctly classified patients with accuracy of 88.0%, sensitivity of 74.3% and specificity of 94.6%. In our external validation experiment, this same deep learning model achieved an accuracy of 80.0%, sensitivity of 61.1%, specificity of 91.5% and AuROC of 0.79. A deep learning model that incorporates clinical data and anatomical T2-weighted MR images might provide a means of risk-stratifying liver stiffness and directing the use of MR elastography.

Magnetic resonance angiography reveals increased arterial blood supply and tumorigenesis following high fat feeding in a mouse model of triple-negative breast cancer.

Breast cancer is the second most commonly diagnosed malignancy among women globally. Past MRI studies have linked a high animal fat diet (HAFD) to increased mammary cancer risk in the SV40Tag mouse model of triple-negative breast cancer. Here, serial MRI examines tumor progression and measures the arterial blood volume feeding mammary glands in low fat diet (LFD) or HAFD fed mice. Virgin female C3(1)SV40Tag mice (n = 8), weaned at 3 weeks old, were assigned to an LFD (n = 4, 3.7 kcal/g, 17.2% kcal from vegetable oil) or an HAFD (n = 4, 5.3 kcal/g, 60% kcal from lard) group. From ages 8 to 12 weeks, weekly fast spin echo MR images and time-of-flight (TOF) MR angiography of inguinal mammary glands were acquired at 9.4 T. Following in vivo MRI, mice were sacrificed. Inguinal mammary glands were excised and fixed for ex vivo MRI and histology. Tumor, blood, and mammary gland volumes for each time point were measured from manually traced regions of interest; tumors were classified as invasive by histopathology-blinded observers. Our analysis confirmed a strong correlation between total tumor volume and blood volume in the mammary gland. Tumor growth rates from weeks 8-12 were twice as high in HAFD-fed mice (0.42 ± 0.14/week) as in LFD-fed mice (0.21 ± 0.03/week), p < 0.004. Mammary gland blood volume growth rate was 2.2 times higher in HAFD mice (0.29 ± 0.11/week) compared with LFD mice (0.13 ± 0.06/week), p < 0.02. The mammary gland growth rate of HAFD-fed mice (0.071 ± 0.011/week) was 2.7 times larger than that of LFD-fed mice (0.026 ± 0.009/week), p < 0.01. This is the first non-invasive, in vivo MRI study to demonstrate a strong correlation between an HAFD and increased cancer burden and blood volume in mammary cancer without using contrast agents, strengthening the evidence supporting the adverse effects of an HAFD on mammary cancer. These results support the potential future use of TOF angiography to evaluate vasculature of suspicious lesions.

Threshold-based quantification of fatty degeneration in the supraspinatus muscle on MRI as an alternative method to Goutallier classification and single-voxel MR spectroscopy

BackgroundConventional fat quantification methods for rotator cuff muscles have various limitations, such as inconsistent reliabilities of the Goutallier grades and need for advanced techniques in quantitative MRI sequences. We aimed to examine a threshold-based fat quantification method in the supraspinatus muscle on standard T1-weighted MR images and compare the threshold-based method with Goutallier grades and MR spectroscopy.MethodsWe retrospectively examined 38 symptomatic patients, who underwent T1 and T2-weighted fast spin-echo MR imaging and a single voxel spin-echo MR spectroscopy. The supraspinatus muscle and fossa were manually segmented in T1-weighted sagittal images and clustering-based thresholding was applied to quantify the fat fractions in the segmented areas using custom MATLAB software. Threshold-based fat fractions were compared with the Goutallier grades and MR spectroscopy fat/water ratios. A one-way analysis of variance and Pearson correlation were tested in the MATLAB software.ResultsInter-observer reliability of threshold-based fat fractions for the supraspinatus muscle and fossa were 0.977 and 0.990 respectively, whereas the reliability of the Goutallier grading was 0.798. Threshold-based fat fractions in the supraspinatus fossa were significantly different between various Goutallier grades (one-way ANOVA, p < 0.001). Threshold-based fat fractions in the supraspinatus muscle strongly correlated with the MR spectroscopy fat/water ratio (Pearson correlation R-square = 0.83).ConclusionsThreshold-based fat quantification on standard T1-weighted MR images was highly reliable and produced comparable results to conventional Goutallier grades and MR spectroscopy fat/water ratios and could serve as an alternative method for accurate fat quantification in rotator cuff muscles.

Standard Normal Fetal Lung Volume by MRI Measurement

Background: Pulmonary hypoplasia is a significant decrease in lung volume by any cause in comparison to the normal volume for gestational age. Objectives: To evaluate the application of prenatal magnetic resonance imaging in order to predict pulmonary hypoplasia, measurement of fetal lung volume (FLV) was aimed to establish a reference data in normal fetuses. Patients and Methods: Three hundred forty two fetuses with abnormal ultrasound findings underwent fast spin-echo T2-weighted MR imaging at a single tertiary care hospital (Shahid Faghihi Hospital, Shiraz, Iran). Data of 241 fetuses at 18 - 36 weeks’ gestation without thoracic malformations were obtained for a FLV normative curve. To acquire a best-fit formula for the mean total fetal lung volume based on each gestational week with 95% confidence interval (CI), we used the regression model applied by Rypens et al. This resulted in a formula calculating the expected fetal lung volume based on gestational age. A one-sample t-test was also carried out to compare the mean total fetal lung volume at each gestational week with the expected mean total fetal lung volume predicted by the formula by Rypens et al., Meyers et al., and Osada et al. Results: Normal FLV increased with gestational age as the spread of values. The expected fetal lung volume was derived from the following formula: Fetal lung volume (mL) = 0.002 × (gestational age [GA]2.913), in which GA is gestational weeks. FLV in our population had a more consistent correlation with Japanese fetuses than European or American fetuses. Conclusion: In fetuses with normal lungs, FLV distribution against gestational age is simply measured prenatally with MR imaging. A single universal formula might not be suitable for fetuses worldwide. In our region, acquired data were more consistent with Asian normal values.

Three Dimensional Positive Contrast Susceptibility Fast Spin Echo MR Imaging with Variable Excitation Pulses and PD Algorithm.

A susceptibility-based positive contrast MR technique is applied to image the MR compatible metallic devices by solving a regularized ℓ1 minimization problem. However, the previous SE/FSE sequence is used for the data acquisition which can result in high SAR and low sampling efficiency in 3D imaging. Therefore, a 3D single slab 3D FSE sequence with slab selective and variable excitation pulse is proposed to implement 3D positive contrast MR imaging for low SAR and acquiring high-resolution 3D images within a shorter timeframe. Furthermore, in order to achieve faster reconstruction and better imaging quality of the 3D positive contrast MRI, the primal-dual iteration algorithm is also used to solve the regularized ℓ1 minimization problem. The visualization of the positive contrast and convergence behaviour of the proposed reconstruction framework base on the first-order PD algorithm were tested and validated on phantom experiments, compared with the previous nonlinear conjugate gradient (NLCG), fast iterative soft thresholding (FISTA) and alternating direction method of multipliers (ADMM) algorithms.

Fully Automated Diagnosis of Anterior Cruciate Ligament Tears on Knee MR Images by Using Deep Learning.

To investigate the feasibility of using a deep learning-based approach to detect an anterior cruciate ligament (ACL) tear within the knee joint at MRI by using arthroscopy as the reference standard. A fully automated deep learning-based diagnosis system was developed by using two deep convolutional neural networks (CNNs) to isolate the ACL on MR images followed by a classification CNN to detect structural abnormalities within the isolated ligament. With institutional review board approval, sagittal proton density-weighted and fat-suppressed T2-weighted fast spin-echo MR images of the knee in 175 subjects with a full-thickness ACL tear (98 male subjects and 77 female subjects; average age, 27.5 years) and 175 subjects with an intact ACL (100 male subjects and 75 female subjects; average age, 39.4 years) were retrospectively analyzed by using the deep learning approach. Sensitivity and specificity of the ACL tear detection system and five clinical radiologists for detecting an ACL tear were determined by using arthroscopic results as the reference standard. Receiver operating characteristic (ROC) analysis and two-sided exact binomial tests were used to further assess diagnostic performance. The sensitivity and specificity of the ACL tear detection system at the optimal threshold were 0.96 and 0.96, respectively. In comparison, the sensitivity of the clinical radiologists ranged between 0.96 and 0.98, while the specificity ranged between 0.90 and 0.98. There was no statistically significant difference in diagnostic performance between the ACL tear detection system and clinical radiologists at P < .05. The area under the ROC curve for the ACL tear detection system was 0.98, indicating high overall diagnostic accuracy. There was no significant difference between the diagnostic performance of the ACL tear detection system and clinical radiologists for determining the presence or absence of an ACL tear at MRI.© RSNA, 2019Supplemental material is available for this article.

Case 267.

History A 28-year-old man presented with lifelong anejaculation, which had become an issue because of family planning. The patient had a history of normal erections and experienced the sensation of orgasm without ever ejaculating. On physical examination, both testes were present in the scrotum, with normal dimensions and a normal epididymis bilaterally. The patient had a slightly tender left testicle, and digital rectal examination findings were normal. The patient underwent further investigation for the possibility of retrograde ejaculation with urine cytology, the results of which were negative. Genetic testing was performed to exclude Y chromosome microdeletions. Serum-luteinizing and follicle-stimulating hormone levels were normal, with a borderline low level of testosterone (7.6 nmol/L; normal range, 8.0-29.0 nmol/L). All other pertinent laboratory results were noncontributory. Pelvic MRI was requested to exclude an anatomic cause of anejaculation. MRI was performed in accordance with the standard clinical prostate protocol, with a dynamic contrast material-enhanced study ( Figs 1 - 3 ). CT of the upper abdomen was also performed ( Fig 4 ). The patient subsequently underwent cystoscopy, which revealed an intravesicular fluid-filled mass near the left ureteric orifice ( Fig 5 ). Figure 1a: (a) Coronal and (b, c) axial fast spin-echo T2-weighted MR images of the pelvis, with b being superior to c. Figure 1b: (a) Coronal and (b, c) axial fast spin-echo T2-weighted MR images of the pelvis, with b being superior to c. Figure 1c: (a) Coronal and (b, c) axial fast spin-echo T2-weighted MR images of the pelvis, with b being superior to c. Figure 2a: (a) Coronal T2-weighted (repetition time msec/echo time msec, 4574/86.5) MR image of the pelvis. (b) Axial T2-weighted (3000/85.4) MR image of the pelvis. Figure 2b: (a) Coronal T2-weighted (repetition time msec/echo time msec, 4574/86.5) MR image of the pelvis. (b) Axial T2-weighted (3000/85.4) MR image of the pelvis. Figure 3: Unenhanced axial fat-saturated T1-weighted (6.2/3.1) MR images. Figure 4: Coronal CT urogram. Figure 5: Image obtained at cystoscopy.

Non-alcoholic fatty liver disease in underweight patients with inflammatory bowel disease: A case-control study.

Non-alcoholic fatty liver disease (NAFLD) was shown to also occur in lean and underweight patients. So far, the prevalence of NAFLD in underweight individuals with and without inflammatory bowel disease (IBD) is insufficiently enlightened. In this cross-sectional age, gender and disease-matched case-control study, underweight patients (BMI<18.5 kg/m2) with inflammatory bowel disease (IBD), who underwent abdominal MRI at 1.5 T/3 T with fat-saturated fast-spin-echo imaging from 10/2005-07/2018 were analysed (control-to-case-ratio 1:1, n = 130). All patients were additionally investigated for duration, history of surgery, medical treatment, laboratory values, liver and spleen diameters. On MRI, liver fat was quantified by two observers based on the relative signal loss on T2-weighted fast spin-echo MR images with fat saturation compared to images without fat saturation. The prevalence of NAFLD/liver steatosis, defined as a measured intrahepatic fat content of at least 5%, was significantly higher in underweight IBD patients than in normal weight patients (87.6% versus 21.5%, p<0.001). Compared to the cases, the liver fat content of the controls was reduced by -0.19 units on average (-19%; 95%Cl: -0.20; -0.14). Similar results were obtained for the subgroup of non-IBD individuals (n = 12; -0.25 units on average (-25%); 95%Cl: -0.35; -0.14). Patients with extremely low body weight (BMI <17.5 kg/m2) showed the highest liver fat content (+0.15 units on average (+15%) compared to underweight patients with a BMI of 17.5–18.5 kg/m2 (p<0.05)). Furthermore, underweight patients showed slightly increased liver enzymes and liver diameters. There were no indications of significant differences in disease duration, type of medications or surgery between cases and controls and also, there were no significant differences between observers or field strengths (p>0.05). The prevalence of liver steatosis was higher among underweight IBD and non-IBD patients compared to normal weight controls. Also, underweight patients showed slightly increased liver enzymes and liver diameters, hinting at initial metabolic disturbances.

Intermediate Weighted Fast Spin Echo (IW FSE) MR Imaging of Hyaline Cartilage Defects of the Knee: Comparison with the Fat Suppressed Three Dimensional Gradient Echo (3D SPGR) Imaging and Arthroscopy

Intermediate Weighted Fast Spin Echo (IW FSE) MR Imaging of Hyaline Cartilage Defects of the Knee: Comparison with the Fat Suppressed Three Dimensional Gradient Echo (3D SPGR) Imaging and Arthroscopy

Deep convolutional neural network for segmentation of knee joint anatomy.

To describe and evaluate a new segmentation method using deep convolutional neural network (CNN), 3D fully connected conditional random field (CRF), and 3D simplex deformable modeling to improve the efficiency and accuracy of knee joint tissue segmentation. A segmentation pipeline was built by combining a semantic segmentation CNN, 3D fully connected CRF, and 3D simplex deformable modeling. A convolutional encoder-decoder network was designed as the core of the segmentation method to perform high resolution pixel-wise multi-class tissue classification for 12 different joint structures. The 3D fully connected CRF was applied to regularize contextual relationship among voxels within the same tissue class and between different classes. The 3D simplex deformable modeling refined the output from 3D CRF to preserve the overall shape and maintain a desirable smooth surface for joint structures. The method was evaluated on 3D fast spin-echo (3D-FSE) MR image data sets. Quantitative morphological metrics were used to evaluate the accuracy and robustness of the method in comparison to the ground truth data. The proposed segmentation method provided good performance for segmenting all knee joint structures. There were 4 tissue types with high mean Dice coefficient above 0.9 including the femur, tibia, muscle, and other non-specified tissues. There were 7 tissue types with mean Dice coefficient between 0.8 and 0.9 including the femoral cartilage, tibial cartilage, patella, patellar cartilage, meniscus, quadriceps and patellar tendon, and infrapatellar fat pad. There was 1 tissue type with mean Dice coefficient between 0.7 and 0.8 for joint effusion and Baker's cyst. Most musculoskeletal tissues had a mean value of average symmetric surface distance below 1 mm. The combined CNN, 3D fully connected CRF, and 3D deformable modeling approach was well-suited for performing rapid and accurate comprehensive tissue segmentation of the knee joint. The deep learning-based segmentation method has promising potential applications in musculoskeletal imaging.

PET Imaging Stability Measurements During Simultaneous Pulsing of Aggressive MR Sequences on the SIGNA PET/MR System.

The recent introduction of simultaneous whole-body PET/MR scanners has enabled new research taking advantage of the complementary information obtainable with PET and MRI. One such application is kinetic modeling, which requires high levels of PET quantitative stability. To accomplish the required PET stability levels, the PET subsystem must be sufficiently isolated from the effects of MR activity. Performance measurements have previously been published, demonstrating sufficient PET stability in the presence of MR pulsing for typical clinical use; however, PET stability during radiofrequency (RF)-intensive and gradient-intensive sequences has not previously been evaluated for a clinical whole-body scanner. In this work, PET stability of the GE SIGNA PET/MR was examined during simultaneous scanning of aggressive MR pulse sequences. Methods: PET performance tests were acquired with MR idle and during simultaneous MR pulsing. Recent system improvements mitigating RF interference and gain variation were used. A fast recovery fast spin echo MR sequence was selected for high RF power, and an echo planar imaging sequence was selected for its high heat-inducing gradients. Measurements were performed to determine PET stability under varying MR conditions using the following metrics: sensitivity, scatter fraction, contrast recovery, uniformity, count rate performance, and image quantitation. A final PET quantitative stability assessment for simultaneous PET scanning during functional MRI studies was performed with a spiral in-and-out gradient echo sequence. Results: Quantitation stability of a 68Ge flood phantom was demonstrated within 0.34%. Normalized sensitivity was stable during simultaneous scanning within 0.3%. Scatter fraction measured with a 68Ge line source in the scatter phantom was stable within the range of 40.4%-40.6%. Contrast recovery and uniformity were comparable for PET images acquired simultaneously with multiple MR conditions. Peak noise equivalent count rate was 224 kcps at an effective activity concentration of 18.6 kBq/mL, and the count rate curves and scatter fraction curve were consistent for the alternating MR pulsing states. A final test demonstrated quantitative stability during a spiral functional MRI sequence. Conclusion: PET stability metrics demonstrated that PET quantitation was not affected during simultaneous aggressive MRI. This stability enables demanding applications such as kinetic modeling.

MRI reveals increased tumorigenesis following high fat feeding in a mouse model of triple‐negative breast cancer

High animal fat consumption is associated with an increase in triple-negative breast cancer (TNBC) risk. Based on previous MRI studies demonstrating the feasibility of detecting very early non-palpable mammary cancers in simian virus 40 large T antigen (SV40TAg) mice, we examined the effect of dietary fat fed from weaning to young adulthood in this model of TNBC. Virgin female C3(1)SV40TAg mice (n=16) were weaned at 3-4weeks of age and then fed either a low fat diet (LFD) (n=8, 3.7kcal/g; 17.2% kcal from vegetable oil) or a high animal fat diet (HAFD) (n=8, 5.3kcal/g; 60% kcal from lard). After 8weeks on the diet (12weeks of age), fast spin echo MR images of inguinal mammary glands were acquired at 9.4T. Following in vivo MRI, mice were sacrificed and inguinal mammary glands were excised and formalin fixed for ex vivo MRI. 3D volume-rendered MR images were then correlated with mammary gland histology to assess the glandular parenchyma and tumor burden. Using in vivo MRI, an average of 3.88±1.03 tumors were detected per HAFD-fed mouse compared with an average of 1.25±1.16 per LFD-fed mouse (p<0.007). Additionally, the average tumor volume was significantly higher following HAFD feeding (0.53±0.45mm3 ) compared with LFD feeding (0.20±0.08mm3 , p<0.02). Analysis of ex vivo MR and histology images demonstrated that HAFD mouse mammary glands had denser parenchyma, irregular and enlarged ducts, dilated blood vessels, increased white adipose tissue, and increased tumor invasion. MRI and histological studies of the SV40TAg mice demonstrated that HAFD feeding also resulted in higher cancer incidence and larger mammary tumors. Unlike other imaging methods for assessing environmental effects on mammary cancer growth, MRI allows routine serial measurements and reliable detection of small cancers as well as accurate tumor volume measurements and assessment of the three-dimensional distribution of tumors over time.

High-Resolution 3-T Endorectal Prostate MRI: A Multireader Study of Radiologist Preference and Perceived Interpretive Quality of 2D and 3D T2-Weighted Fast Spin-Echo MR Images.

The goal of this study was to compare the perceived quality of 3-T axial T2-weighted high-resolution 2D and high-resolution 3D fast spin-echo (FSE) endorectal MR images of the prostate. Six radiologists independently reviewed paired 3-T axial T2-weighted high-resolution 2D and 3D FSE endorectal MR images of the prostates of 85 men in two sessions. In the first session (n = 85), each reader selected his or her preferred images; in the second session (n = 28), they determined their confidence in tumor identification and compared the depiction of the prostatic anatomy, tumor conspicuity, and subjective intrinsic image quality of images. A meta-analysis using a random-effects model, logistic regression, and the paired Wilcoxon rank-sum test were used for statistical analyses. Three readers preferred the 2D acquisition (67-89%), and the other three preferred the 3D images (70-80%). The option for one of the techniques was not associated with any of the predictor variables. The 2D FSE images were significantly sharper than 3D FSE (p < 0.001) and significantly more likely to exhibit other (nonmotion) artifacts (p = 0.002). No other statistically significant differences were found. Our results suggest that there are strong individual preferences for the 2D or 3D FSE MR images, but there was a wide variability among radiologists. There were differences in image quality (image sharpness and presence of artifacts not related to motion) but not in the sequences' ability to delineate the glandular anatomy and depict a cancerous tumor.

Proton Density MRI Increases Detection of Cervical Spinal Cord Multiple Sclerosis Lesions Compared with T2-Weighted Fast Spin-Echo.

There is a paucity of literature that supports the Consortium of Multiple Sclerosis Centers guideline that proton density MR imaging is a core spinal cord sequence. We hypothesized that proton density fast spin-echo imaging is superior to T2 fast spin-echo MR imaging for the detection of cervical cord MS lesions. This study compared the detection rate and conspicuity of cervical cord MS lesions on sagittal 1.5T proton density fast spin-echo and T2 fast spin-echo MR imaging. One hundred consecutive patients with MS imaged with 1.5T sagittal proton density fast spin-echo and T2 fast spin-echo cervical cord MR imaging between September 2012 and October 2013 were retrospectively included. The number of MS lesions detected on each sequence was recorded; conspicuity was assessed quantitatively with the lesion-to-cord contrast ratio and lesion-contrast-to-noise ratio. Statistical analysis was performed by using the Wilcoxon signed rank test. Seventy-eight patients had MS cord lesions detected. Proton density fast spin-echo imaging detected a greater number of lesions (n = 181) compared with T2 fast spin-echo imaging (n = 137, P < .001). Fifteen patients (19%) with abnormal findings on proton density fast spin-echo imaging had normal findings on T2 fast spin-echo imaging; no patient with abnormal T2 fast spin-echo imaging findings had normal proton density fast spin-echo imaging findings. Although proton density fast spin-echo and T2 fast spin-echo imaging had similar lesion-to-cord contrast ratios (proton density fast spin-echo, 0.32 ± 0.01, versus T2 fast spin-echo, 0.33 ± 0.01; P = .43), proton density fast spin-echo had greater lesion-contrast-to-noise ratio (proton density fast spin-echo, 82 ± 3.0, versus T2 fast spin-echo, 64 ± 2.6; P < .001). Proton density fast spin-echo imaging is superior to T2 fast spin-echo MR imaging for the detection of cervical cord MS lesions. Proton density fast spin-echo detects cord lesions in patients in whom T2 fast spin-echo findings appear normal. This study forms the evidentiary base for the current Consortium of Multiple Sclerosis Centers guideline that proton density imaging is a core spinal cord sequence.

T2-weighted four dimensional magnetic resonance imaging with result-driven phase sorting.

T2-weighted MRI provides excellent tumor-to-tissue contrast for target volume delineation in radiation therapy treatment planning. This study aims at developing a novel T2-weighted retrospective four dimensional magnetic resonance imaging (4D-MRI) phase sorting technique for imaging organ/tumor respiratory motion. A 2D fast T2-weighted half-Fourier acquisition single-shot turbo spin-echo MR sequence was used for image acquisition of 4D-MRI, with a frame rate of 2-3 frames/s. Respiratory motion was measured using an external breathing monitoring device. A phase sorting method was developed to sort the images by their corresponding respiratory phases. Besides, a result-driven strategy was applied to effectively utilize redundant images in the case when multiple images were allocated to a bin. This strategy, selecting the image with minimal amplitude error, will generate the most representative 4D-MRI. Since we are using a different image acquisition mode for 4D imaging (the sequential image acquisition scheme) with the conventionally used cine or helical image acquisition scheme, the 4D dataset sufficient condition was not obviously and directly predictable. An important challenge of the proposed technique was to determine the number of repeated scans (NR) required to obtain sufficient phase information at each slice position. To tackle this challenge, the authors first conducted computer simulations using real-time position management respiratory signals of the 29 cancer patients under an IRB-approved retrospective study to derive the relationships between NR and the following factors: number of slices (NS), number of 4D-MRI respiratory bins (NB), and starting phase at image acquisition (P0). To validate the authors' technique, 4D-MRI acquisition and reconstruction were simulated on a 4D digital extended cardiac-torso (XCAT) human phantom using simulation derived parameters. Twelve healthy volunteers were involved in an IRB-approved study to investigate the feasibility of this technique. 4D data acquisition completeness (Cp) increases as NR increases in an inverse-exponential fashion (Cp = 100 - 99 × exp(-0.18 × NR), when NB = 6, fitted using 29 patients' data). The NR required for 4D-MRI reconstruction (defined as achieving 95% completeness, Cp = 95%, NR = NR,95) is proportional to NB (NR,95 ∼ 2.86 × NB, r = 1.0), but independent of NS and P0. Simulated XCAT 4D-MRI showed a clear pattern of respiratory motion. Tumor motion trajectories measured on 4D-MRI were comparable to the average input signal, with a mean relative amplitude error of 2.7% ± 2.9%. Reconstructed 4D-MRI for healthy volunteers illustrated clear respiratory motion on three orthogonal planes, with minimal image artifacts. The artifacts were presumably caused by breathing irregularity and incompleteness of data acquisition (95% acquired only). The mean relative amplitude error between critical structure trajectory and average breathing curve for 12 healthy volunteers is 2.5 ± 0.3 mm in superior-inferior direction. A novel T2-weighted retrospective phase sorting 4D-MRI technique has been developed and successfully applied on digital phantom and healthy volunteers.

Abnormal tibiofemoral contact mechanics in subjects with medial and lateral compartment articular cartilage lesions

s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A306 481 ABNORMAL TIBIOFEMORAL CONTACT MECHANICS IN SUBJECTS WITH MEDIAL AND LATERAL COMPARTMENT ARTICULAR CARTILAGE LESIONS S.Y. Segev, D. Kumar, L. Nardo, V. Pedoia, T.M. Link, S. Majumdar, R.B. Souza. Univ. of California San Francisco, San Francisco, CA, USA Purpose: To evaluate the changes in cartilage-on-cartilage contact areas and medial and lateral contact area centroid movement in the tibiofemoral joint during knee flexion and extension using MRI in subjects with and without tibiofemoral cartilage lesion. Methods: Subjects from an observational study on knee Osteoarthritis (OA), including both subjects with andwithout radiographic OA, (n1⁄4 94 Mean age 1⁄4 54.1±10.5 years; Mean BMI 1⁄4: 24.4±3.4 kg/m2; Men:Women 1⁄4 35:59) underwent 2D fast-spin echo (FSE) MR imaging at 0 and 30 of knee flexion under axial loading (25% bodyweight). For subjects with radiographic OA, the more severe knee was enrolled. For subjects without radiographic OA, the enrolled knee was randomly selected. A fluid sensitive-fat-saturated 3D fast spin-echo sequence with variable flip angle (CUBE) was acquired in order to grade cartilage lesions using a semi-quantitative score. Subjects were then stratified into those with and without cartilage lesions at the tibiofemoral joint. Tibiofemoral contact area was defined on FSE images as the area of contact between the tibial and femoral articular cartilage, excluding meniscus contact area and joint fluid. This region of contact was semiautomatically segmented separately in the medial and lateral knee compartment using Bezier-splines created with in-house software written in Matlab. Contact area centroid position was determined by evaluation of the contact area on a defined anatomic coordinate system embedded within the tibia. Differences in medial and lateral contact area at flexed and extended conditions, and medial and lateral contact area centroid translations were compared between subjects with and without cartilage lesions using analysis of co-variance (ANCOVA), adjusted for age, gender, knee alignment, and BMI. Results: Subjects with medial compartment cartilage lesions (n1⁄428) had greater contact area in the affected compartment during extension (Figure 1, 361 vs. 270 mm2; p1⁄40.025), but not flexion (Figure 1, 287 vs. 219mm2; p1⁄40.146) when compared to subjects without lesions (n1⁄466). No differences in contact area in the lateral compartment were observed between subjects with and without medial compartment lesions. In contrast, subjects with lesions in the lateral compartment (n1⁄418) were found to have greater contact area than subjects without lesions (n1⁄476) in both extension (Figure 2, 366 vs. 271 mm2; p1⁄40.009) and flexion (Figure 2, 326 vs. 224 mm2; p1⁄40.002) as well as in the contralateral compartment while in full extension (Figure 2, 374 vs. 279 mm2; p1⁄40.012). With regard to contact kinematics, subjects with medial compartment lesions had greater anterior-posterior translation of the medial contact centroid when moving from extension to flexion (Figure 3, Figure 4, p1⁄40.047). No differences in anterior-posterior centroid translations were observed in either the medial or lateral compartment of subjects with lateral compartment lesions. Conclusions: Contact mechanics in subjects with cartilage lesions are significantly different compared to those without lesions. The higher contact area in subjects with cartilage lesions is likely due to the changes in the ability of the cartilage to adapt to loading, expanding the contact surface as the cartilage adjacent to the lesion gives way to the load. This phenomenon is coupled with abnormal contact kinematics in persons with cartilage lesions. While the normal kinematics of knee flexion requires the femur to slide back on the tibial plateau, our data suggests that the movement in the affected compartment is greater in knees with medial compartment cartilage lesions. This finding could be related to knee instability, an extremely common symptom in patients with OA. Taken together, these differences may be responsible for more rapid cartilage degeneration in individuals with OA. Abstracts / Osteoarthritis and Cartilage 23 (2015) A82eA416 A307s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A307 482 SERUM LEVELS OF RESISTIN AND INTERLEUKIN-17 ARE ASSOCIATED WITH INCREASED CARTILAGE DEFECTS AND BONE MARROW LESIONS IN PATIENTS WITH KNEE SYMPTOMATIC OSTEOARTHRITIS K. Wang y, J. Xu y, J. Cai y, S. Zheng y, X. Yang y, C. Ding zy. yDept. of Rheumatology and Immunology, First Affiliated Hosp. of Anhui Med. Univ., Hefei, China; zMenzies Inst. of Med. Res., Univ. of Tasmania,

Four dimensional magnetic resonance imaging with retrospective k-space reordering: a feasibility study.

Current four dimensional magnetic resonance imaging (4D-MRI) techniques lack sufficient temporal/spatial resolution and consistent tumor contrast. To overcome these limitations, this study presents the development and initial evaluation of a new strategy for 4D-MRI which is based on retrospective k-space reordering. We simulated a k-space reordered 4D-MRI on a 4D digital extended cardiac-torso (XCAT) human phantom. A 2D echo planar imaging MRI sequence [frame rate (F) = 0.448 Hz; image resolution (R) = 256 × 256; number of k-space segments (NKS) = 4] with sequential image acquisition mode was assumed for the simulation. Image quality of the simulated "4D-MRI" acquired from the XCAT phantom was qualitatively evaluated, and tumor motion trajectories were compared to input signals. In particular, mean absolute amplitude differences (D) and cross correlation coefficients (CC) were calculated. Furthermore, to evaluate the data sufficient condition for the new 4D-MRI technique, a comprehensive simulation study was performed using 30 cancer patients' respiratory profiles to study the relationships between data completeness (Cp) and a number of impacting factors: the number of repeated scans (NR), number of slices (NS), number of respiratory phase bins (NP), NKS, F, R, and initial respiratory phase at image acquisition (P0). As a proof-of-concept, we implemented the proposed k-space reordering 4D-MRI technique on a T2-weighted fast spin echo MR sequence and tested it on a healthy volunteer. The simulated 4D-MRI acquired from the XCAT phantom matched closely to the original XCAT images. Tumor motion trajectories measured from the simulated 4D-MRI matched well with input signals (D = 0.83 and 0.83 mm, and CC = 0.998 and 0.992 in superior-inferior and anterior-posterior directions, respectively). The relationship between Cp and NR was found best represented by an exponential function (CP=1001-e(-0.18NR) , when NS = 30, NP = 6). At a CP value of 95%, the relative error in tumor volume was 0.66%, indicating that NR at a CP value of 95% (NR,95%) is sufficient. It was found that NR,95% is approximately linearly proportional to NP (r = 0.99), and nearly independent of all other factors. The 4D-MRI images of the healthy volunteer clearly demonstrated respiratory motion in the diaphragm region with minimal motion induced noise or aliasing. It is feasible to generate respiratory correlated 4D-MRI by retrospectively reordering k-space based on respiratory phase. This new technology may lead to the next generation 4D-MRI with high spatiotemporal resolution and optimal tumor contrast, holding great promises to improve the motion management in radiotherapy of mobile cancers.

Localizer sequences of magnetic resonance imaging accurately identify osteoporotic vertebral fractures

The aim of the present study was to evaluate the performance of sagittal MR localizer (MR-loc), in terms of diagnostic accuracy and intra- and inter-observer agreement in the detection of vertebral fractures (VFs). Three-hundred MR examinations of the thoracic and/or lumbar spine were randomly collected. A semi-quantitative approach was used and morphometric analysis was performed when a VF was suspected. MR-loc images were evaluated blindly by three radiologists in two different sessions. A full diagnostic sagittal T1-weighted fast spin echo MR sequence was used as standard of reference (RS). Degenerative arthritis was also scored on RS. Only vertebral bodies which were assessable by both MR-loc and RS were considered for the analysis. Area under the receiver operating characteristic curve (AUROC), Cohen kappa statistic, and linear-by-linear association were used for statistical analysis. Kappa values were compared by means of the z distribution.A total of 2186 vertebrae were analysed in 300 MRI exams (147 males, 153 females, 59.4±16.4y.o.). Sixty-seven out of 2136 (3.1%) VFs were identified in 23/300 (7.7%) patients submitted to MRI. In the detection of VFs, sensitivity and specificity of MR-loc were both 100% (accuracy AUROC=1.000). Inter-observer agreement was excellent (k=0.938±0.013), while intra-observer agreement was perfect (k=1.000). The diagnostic performance was independent from degenerative arthritis, vertebral level, type and grade of VFs.MR-loc is a simple but accurate tool in the detection of VFs. It should be introduced for systematic evaluation in the detection of VFs in MR examinations performed in daily clinical practice.

Isotropic three‐dimensional MRI‐Fricke‐infused gel dosimetry

Fricke-infused gel has been shown to be a simple and attainable method for the conformal measurement of absorbed radiation dose. Nevertheless, its accuracy is seriously hindered by the irreversible ferric ion diffusion during magnetic resonance imaging, particularly when three-dimensional (3D) dose measurement in radiosurgery is considered. In this study, the authors developed a fast three-dimensional spin-echo based Fricke gel dosimetry technique to reduce the adverse effects of ferric ion diffusion and to obtain an accurate isotropic 3D dose measurement. A skull shaped phantom containing Fricke-infused gel was irradiated using Leksell Gamma Knife. The rapid image-based dosimetry technique was applied with the use of a 3D fast spin-echo magnetic resonance imaging sequence. The authors mathematically derived and experimentally validated the correlations between dose-response characteristics and parameters of the 3D fast spin-echo MR imaging sequence. Absorbed dose profiles were assessed and compared to the calculated profiles given by the Gamma Knife treatment planning system. Coefficient of variance (CV%) and coefficient of determination (R(2)) were used to evaluate the precision of dose-response curve estimation. The agreement between the measured and the planned 3D dose distributions was quantified by gamma-index analysis of two acceptance criteria. Proper magnetic resonance imaging parameters were explored to render an accurate three-dimensional absorbed dose mapping with a 1 mm(3) isotropic image resolution. The efficacy of the dose-response estimation was approved by an R(2) > 0.99 and an average CV% of 1.6%. Average gamma pass-rate between the experimentally measured and GammaPlan calculated dose distributions were 83.8% and 99.7% for 2%/2 and 3%/3 mm criteria, respectively. With the designed MR imaging sequence and parameters, total 3D MR acquisition time was confined to within 20 min postirradiation, during which time ferric ion diffusion effects were negligible, thus enabling an accurate 3D radiation dose measurement.