Sparse-SEMAC: rapid and improved SEMAC metal implant imaging using SPARSE-SENSE acceleration.

PURPOSE: To develop an accelerated SEMAC metal implant MRI technique (Sparse-SEMAC) with reduced scan time and improved metal distortion correction. METHODS: Sparse-SEMAC jointly exploits the inherent sparsity along the additional phase-encoding dimension and multicoil encoding capabilities to significantly accelerate data acquisition. A prototype pulse sequence with pseudorandom ky -kz undersampling and an inline image reconstruction was developed for integration in clinical studies. Three patients with hip implants were imaged using the proposed Sparse-SEMAC with eight-fold acceleration and compared with the standard-SEMAC technique used in clinical studies (three-fold GRAPPA acceleration). Measurements were performed with SEMAC-encoding steps (SES) = 15 for Sparse-SEMAC and SES = 9 for Standard-SEMAC using high spatial resolution Proton Density (PD) and lower-resolution STIR acquisitions. Two expert musculoskeletal (MSK) radiologists performed a consensus reading to score image-quality parameters. RESULTS: Sparse-SEMAC enables up to eight-fold acceleration of data acquisition that results in two-fold scan time reductions, compared with Standard-SEMAC, with improved metal artifact correction for patients with hip implants without degrading spatial resolution. CONCLUSION: The high acceleration enabled by Sparse-SEMAC would enable clinically feasible examination times with improved correction of metal distortion. Magn Reson Med 78:79-87, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Voxelwise analysis of simultaneously acquired and spatially correlated 18 F-fluorodeoxyglucose (FDG)-PET and intravoxel incoherent motion metrics in breast cancer.

PURPOSE: Diffusion-weighted imaging (DWI) and 18 F-fluorodeoxyglucose-positron emission tomography (18 F-FDG-PET) independently correlate with malignancy in breast cancer, but the relationship between their structural and metabolic metrics is not completely understood. This study spatially correlates diffusion, perfusion, and glucose avidity in breast cancer with simultaneous PET/MR imaging and compares correlations with clinical prognostics. METHODS: In this Health Insurance Portability and Accountability Act-compliant prospective study, with written informed consent and approval of the institutional review board and using simultaneously acquired FDG-PET and DWI, tissue diffusion (Dt ), and perfusion fraction (fp ) from intravoxel incoherent motion (IVIM) analysis were registered to FDG-PET within 14 locally advanced breast cancers. Lesions were analyzed using 2D histograms and correlation coefficients between Dt , fp , and standardized uptake value (SUV). Correlations were compared with prognostics from biopsy, metastatic burden from whole-body PET, and treatment history. RESULTS: SUV||Dt correlation coefficient significantly distinguished treated (0.11 ± 0.24) from nontreated (-0.33 ± 0.26) patients (P = 0.005). SUV||fp correlations were on average negative for the whole cohort (-0.17 ± 0.13). CONCLUSION: Simultaneously acquired and registered FDG-PET/DWI allowed quantifiable descriptions of breast cancer microenvironments that may provide a framework for monitoring and predicting response to treatment. Magn Reson Med 78:1147-1156, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Polarized multichannel transmit MRI to reduce shading near metal implants.

PURPOSE: To investigate the benefit of a two-channel transmit system on shading close to total hip replacements and other elongated metal structures in parallel to the magnet bore. METHODS: An analytical model comprising a water cylinder and a metal rod is introduced to describe the B1 effects close to elongated metal structures and it is verified. The dependence of the optimal polarization, which induces minimum shading, on the position of the metal is analyzed. Furthermore, the optimal polarization for two patients is determined both on the basis of the model and experimentally and its benefit compared with circular polarization is investigated. RESULTS: The cylindrical model approximates the modification of the B1 field due to the metal well, and the optimal polarization strongly depends on the position of the rod. In vivo, shading can be ameliorated by the use of the optimal polarization; for total hip replacements with shafts of titanium, this polarization can be determined on the basis of both the analytical model and the experimental data. CONCLUSION: Parallel transmission offers the possibility of a substantial reduction of shading close to long metal structures in parallel to the magnet bore.

Dynamic contrast-enhanced MRI of the prostate with high spatiotemporal resolution using compressed sensing, parallel imaging, and continuous golden-angle radial sampling: preliminary experience.

PURPOSE: To demonstrate dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) of the prostate with both high spatial and temporal resolution via a combination of golden-angle radial k-space sampling, compressed sensing, and parallel-imaging reconstruction (GRASP), and to compare image quality and lesion depiction between GRASP and conventional DCE in prostate cancer patients. MATERIALS AND METHODS: Twenty prostate cancer patients underwent two 3T prostate MRI examinations on separate dates, one using standard DCE (spatial resolution 3.0 × 1.9 × 1.9 mm, temporal resolution 5.5 sec) and the other using GRASP (spatial resolution 3.0 × 1.1 × 1.1 mm, temporal resolution 2.3 sec). Two radiologists assessed measures of image quality and dominant lesion size. The experienced reader recorded differences in contrast arrival times between the dominant lesion and benign prostate. RESULTS: Compared with standard DCE, GRASP demonstrated significantly better clarity of the capsule, peripheral/transition zone boundary, urethra, and periprostatic vessels; image sharpness; and lesion conspicuity for both readers (P < 0.001-0.020). GRASP showed improved interreader correlation for lesion size (GRASP: r = 0.691-0.824, standard: r = 0.495-0.542). In 8/20 cases, only GRASP showed earlier contrast arrival in tumor than benign; in no case did only standard DCE show earlier contrast arrival in tumor. CONCLUSION: High spatiotemporal resolution prostate DCE is possible with GRASP, which has the potential to improve image quality and lesion depiction as compared with standard DCE.

Diffusion-weighted imaging of the liver: comparison of image quality between monopolar and bipolar acquisition schemes at 3T.

PURPOSE: To compare image quality of monopolar and bipolar diffusion-weighted imaging (DWI) sequences of the liver at 3T. METHODS: 32 healthy volunteers (mean 27 ± 8 years; 27 M/5F) and 11 patients (mean age 58 ± 14 years; 8 M/3F) underwent liver MRI using a 3T system incorporating 2-channel parallel transmission for B1-shimming and reduced B1-inhomogeneity. Scans included free-breathing DWI sequences (b-value 0, 400, 800 s/mm(2)) acquired using both monopolar and bipolar techniques. Estimated signal-to-noise ratio (eSNR), apparent diffusion coefficient (ADC), and measures of subjective image quality on b-800 images, scored on a 1-5 scale by two independent radiologists, were compared between sequences. RESULTS: Monopolar sequence demonstrated significantly higher eSNR (volunteers: 12.7 ± 4.0 vs. 11.3 ± 3.5, patients: 11.4 ± 4.0 vs. 10.2 ± 3.3; p ≤ 0.013) compared with the bipolar sequence. Monopolar sequence also achieved significantly higher scores for reader 1 in volunteers and patients in terms of clarity of right lobe edge, clarity of intra-hepatic vessels, conspicuity of the left lobe, and overall diagnostic quality (p ≤ 0.031), as well as significantly higher scores for reader 2 in volunteers in terms of clarity of intra-hepatic vessels, conspicuity of the left lobe, and overall diagnostic quality (p ≤ 0.035). Respiratory motion artifact was not significantly different between sequences in patients or volunteers for either reader (p ≥ 0.191). Hepatic ADC was significantly lower using monopolar technique only in volunteers (1.28 ± 0.12 vs. 1.43 ± 0.15, p < 0.001). CONCLUSION: In comparison with past studies performed at 1.5T, when using a modern 3T system, we observed improved image quality of liver DWI using a monopolar, rather than a bipolar, acquisition scheme, largely attributed to higher eSNR.

Zoomed echo-planar imaging using parallel transmission: impact on image quality of diffusion-weighted imaging of the prostate at 3T.

PURPOSE: To assess impact of two-channel parallel transmission (pTx) with focused excitation [zoomed echo-planar imaging (EPI)] on image quality of prostate diffusion-weighted imaging (DWI) at 3T. METHODS: 27 male volunteers (27 ± 8 years) underwent 3T prostate MRI using 2-channel radiofrequency-transmit system and 18-channel torso receive coil. Scans included EPI-DWI sequence (b values 50, 500, 1000 s/mm(2)) acquired both with standard sinc pulse and 2-channel pTX with focused excitation, each acquired at large-field-of-view (FOV) (20 × 20 cm) and small-FOV (14 × 14 cm). An abdominal radiologist scored b-1000 images and ADC maps for image quality measures. Sequences were compared using paired Wilcoxon tests. RESULTS: pTx with focused excitation showed significant improvements compared with standard DWI on b-1000 images at large-FOV for the absence of wrap and overall image quality (p ≤ 0.049); on b-1000 images at small-FOV for reduced distortion of prostate, absence of ghosting, absence of wrap, clarity of prostate capsule, clarity of peripheral/transition zone boundary, clarity of peri-urethral region, and overall image quality (p ≤ 0.004); and on ADC maps at small-FOV for reduced distortion of prostate, sharpness of prostate, clarity of prostatic capsule, clarity of peri-urethral region, and overall image quality (p = 0.002-0.036). When compared with standard large-FOV images, small-FOV images obtained using pTx with focused excitation showed no significant difference on the b-1000 images for any feature (p ≥ 0.175), while showing significant improvements on the ADC maps in terms of reduced distortion, absence of ghosting, and absence of wrap (p = 0.010-0.030). CONCLUSION: Zoomed DWI using 2-channel pTx reduced artifacts and improved image quality for 3T prostate DWI; benefit was most apparent for small-FOV images.

Breast MRI at 7 Tesla with a bilateral coil and robust fat suppression.

PURPOSE: To develop a bilateral coil and fat suppressed T1-weighted sequence for 7 Tesla (T) breast MRI. MATERIALS AND METHODS: A dual-solenoid coil and three-dimensional (3D) T1w gradient echo sequence with B1+ insensitive fat suppression (FS) were developed. T1w FS image quality was characterized through image uniformity and fat-water contrast measurements in 11 subjects. Signal-to-noise ratio (SNR) and flip angle maps were acquired to assess the coil performance. Bilateral contrast-enhanced and unilateral high resolution (0.6 mm isotropic, 6.5 min acquisition time) imaging highlighted the 7T SNR advantage. RESULTS: Reliable and effective FS and high image quality was observed in all subjects at 7T, indicating that the custom coil and pulse sequence were insensitive to high-field obstacles such as variable tissue loading. 7T and 3T image uniformity was similar (P=0.24), indicating adequate 7T B1+ uniformity. High 7T SNR and fat-water contrast enabled 0.6 mm isotropic imaging and visualization of a high level of fibroglandular tissue detail. CONCLUSION: 7T T1w FS bilateral breast imaging is feasible with a custom radiofrequency (RF) coil and pulse sequence. Similar image uniformity was achieved at 7T and 3T, despite different RF field behavior and variable coil-tissue interaction due to anatomic differences that might be expected to alter magnetic field patterns.

Contrast-enhanced radial 3D fat-suppressed T1-weighted gradient-recalled echo sequence versus conventional fat-suppressed contrast-enhanced T1-weighted studies of the head and neck.

OBJECTIVE: Traditional fat-suppressed T1-weighted spin-echo or turbo spin-echo (TSE) sequences (T1-weighted images) may be degraded by motion and pulsation artifacts in head-and-neck studies. Our purpose is to evaluate the role of a fat-suppressed T1-weighted 3D radial gradient-recalled echo sequence (radial-volumetric interpolated breath-hold examination [VIBE]) in the head and neck as compared with standard contrast-enhanced fat-suppressed T1-weighted images. MATERIALS AND METHODS: We retrospectively evaluated 21 patients (age range, 9-67 years) who underwent head-and-neck MRI at 1.5 T. Both contrast-enhanced radial-VIBE and conventional fat-suppressed TSE contrast-enhanced T1-weighted imaging were performed. Two radiologists evaluated multiple parameters of image quality, graded on a 5-point scale. Mixed-model analysis of variance and interobserver variability assessment were performed. RESULTS: The following parameters were scored as significantly better for the contrast-enhanced radial-VIBE sequence than for conventional contrast-enhanced T1-weighted imaging: overall image quality (p < 0.0001), degree of fat suppression (p = 0.006), mucosal enhancement (p = 0.004), muscle edge clarity (p = 0.049), vessel clarity (p < 0.0001), respiratory motion artifact (p = 0.002), pulsation artifact (p < 0.0001), and lesion edge sharpness (p = 0.004). Interobserver agreement in qualitative evaluation of the two sequences showed fair-to-good agreement for the following variables: overall image quality (intraclass correlation coefficient [ICC], 0.779), degree of fat suppression (ICC, 0.716), mucosal enhancement (ICC, 0.693), muscle edge clarity (ICC, 0.675), respiratory motion artifact (ICC, 0.516), lesion enhancement (ICC, 0.410), and lesion edge sharpness (ICC, 0.538). Excellent agreement was shown for vessel clarity (ICC, 0.846) and pulsation artifact (ICC, 0.808). CONCLUSION: The radial-VIBE sequence is a viable motion-robust improvement on the conventional fat-suppressed T1-weighted sequence.

Pulmonary nodules in patients with primary malignancy: comparison of hybrid PET/MR and PET/CT imaging.

PURPOSE: To assess diagnostic sensitivity of radial T1-weighted gradient-echo (radial volumetric interpolated breath-hold examination [VIBE]) magnetic resonance (MR) imaging, positron emission tomography (PET), and combined simultaneous PET and MR imaging with an integrated PET/MR system in the detection of lung nodules, with combined PET and computed tomography (CT) as a reference. MATERIALS AND METHODS: In this institutional review board-approved HIPAA-compliant prospective study, 32 patients with tumors who underwent clinically warranted fluorine 18 ((18)F) fluorodeoxyglucose (FDG) PET/CT followed by PET/MR imaging were included. In all patients, the thorax station was examined with free-breathing radial VIBE MR imaging and simultaneously acquired PET data. Presence and size of nodules and FDG avidity were assessed on PET/CT, radial VIBE, PET, and PET/MR images. Percentage of nodules detected on radial VIBE and PET images was compared with that on PET/MR images by using generalized estimating equations. Maximum standardized uptake value (SUVmax) in pulmonary nodules with a diameter of at least 1 cm was compared between PET/CT and PET/MR imaging with Pearson rank correlation. RESULTS: A total of 69 nodules, including 45 FDG-avid nodules, were detected with PET/CT. The sensitivity of PET/MR imaging was 70.3% for all nodules, 95.6% for FDG-avid nodules, and 88.6% for nodules 0.5 cm in diameter or larger. PET/MR imaging had higher sensitivity than PET for all nodules (70.3% vs 61.6%, P = .002) and higher sensitivity than MR imaging for FDG-avid nodules (95.6% vs 80.0%, P = .008). There was a significantly strong correlation between SUVmax of pulmonary nodules obtained with PET/CT and that obtained with PET/MR imaging (r = 0.96, P < .001). CONCLUSION: Radial VIBE and PET data acquired simultaneously with PET/MR imaging have high sensitivity in the detection of FDG-avid nodules and nodules 0.5 cm in diameter or larger, with low sensitivity for small non-FDG-avid nodules.

Application of time-resolved angiography with stochastic trajectories (TWIST)-Dixon in dynamic contrast-enhanced (DCE) breast MRI.

PURPOSE: To evaluate a magnetic resonance imaging (MRI) technique that integrates time-resolved angiography with stochastic trajectories (TWIST) view sharing and Dixon for a breast dynamic contrast-enhanced (DCE)-MRI application. MATERIALS AND METHODS: Simulation study: K-space data at six timepoints (1 pre-, 5 postcontrast) were generated by performing Fourier transform on a digital "phantom" with 3-9 mm enhancing lesions and three types of enhancement curves (persistent, plateau, washout). Images were reconstructed with and without TWIST. Clinical study: Six TWIST-Dixon image sets (one pre-, five postcontrast) were acquired in 18 patients on a 3T scanner, followed by one conventional image set. The last TWIST-Dixon and the conventional images were scored for seven criteria: perceived signal-to-noise ratio (P.SNR), visualization of anatomy, fat suppression (FS) accuracy, FS uniformity, ghosting artifact, edge ringing artifact, and overall image quality (IQ). RESULTS: Simulation study: With proper TWIST parameters (pA ≥33%, pB ≥50%), the enhancement underestimation was 5% or less for tumor size ≥5 mm. Clinical study: TWIST-Dixon images have significantly better scores in all criteria except for ghosting artifacts, where the difference was not significant. CONCLUSION: With proper parameters, TWIST-Dixon provides higher perceived SNR, more accurate fat suppression, and better overall image quality for breast DCE-MRI without sacrificing accuracy in the enhancement estimation.

Computed diffusion-weighted imaging of the prostate at 3 T: impact on image quality and tumour detection.

OBJECTIVES: To investigate the impact of prostate computed diffusion-weighted imaging (DWI) on image quality and tumour detection. METHODS: Forty-nine patients underwent 3-T magnetic resonance imaging using a pelvic phased-array coil before prostatectomy, including DWI with b values of 50 and 1,000 s/mm(2). Computed DW images with b value 1,500 s/mm(2) were generated from the lower b-value images. Directly acquired b-1,500 DW images were obtained in 39 patients. Two radiologists independently assessed DWI for image quality measures and location of the dominant lesion. A third radiologist measured tumour-to-peripheral-zone (PZ) contrast. Pathological findings from prostatectomy served as the reference standard. RESULTS: Direct and computed b-1,500 DWI showed better suppression of benign prostate tissue than direct b-1,000 DWI for both readers (P ≤ 0.024). However, computed b-1,500 DWI showed less distortion and ghosting than direct b-1,000 and direct b-1,500 DWI for both readers (P ≤ 0.067). Direct and computed b-1,500 images showed better sensitivity and positive predictive value (PPV) for tumour detection than direct b-1,000 images for both readers (P ≤ 0.062), with no difference in sensitivity or PPV between direct and computed b-1,500 images (P ≥ 0.180). Tumour-to-PZ contrast was greater on computed b-1,500 than on either direct DWI set (P < 0.001). CONCLUSION: Computed DWI of the prostate using b value ≥1,000 s/mm(2) improves image quality and tumour detection compared with acquired standard b-value images. KEY POINTS: • Diffusion weighted MRI is increasingly used for diagnosing and assessing prostate carcinoma. • Prostate computed DWI can extrapolate high b-value images from lower b values. • Computed DWI provides greater suppression of benign tissue than lower b-value images. • Computed DWI provides less distortion and artefacts than images using same b value. • Computed DWI provides better diagnostic performance than lower b-value images.

Breast MRI at 7 Tesla with a bilateral coil and T1-weighted acquisition with robust fat suppression: image evaluation and comparison with 3 Tesla.

OBJECTIVES: To evaluate the image quality of T1-weighted fat-suppressed breast MRI at 7 T and to compare 7-T and 3-T images. METHODS: Seventeen subjects were imaged using a 7-T bilateral transmit-receive coil and 3D gradient echo sequence with adiabatic inversion-based fat suppression (FS). Images were graded on a five-point scale and quantitatively assessed through signal-to-noise ratio (SNR), fibroglandular/fat contrast and signal uniformity measurements. RESULTS: Image scores at 7 and 3 T were similar on standard-resolution images (1.1 × 1.1 × 1.1-1.6 mm(3)), indicating that high-quality breast imaging with clinical parameters can be performed at 7 T. The 7-T SNR advantage was underscored on 0.6-mm isotropic images, where image quality was significantly greater than at 3 T (4.2 versus 3.1, P ≤ 0.0001). Fibroglandular/fat contrast was more than two times higher at 7 T than at 3 T, owing to effective adiabatic inversion-based FS and the inherent 7-T signal advantage. Signal uniformity was comparable at 7 and 3 T (P < 0.05). Similar 7-T image quality was observed in all subjects, indicating robustness against anatomical variation. CONCLUSION: The 7-T bilateral transmit-receive coil and adiabatic inversion-based FS technique produce image quality that is as good as or better than at 3 T. KEY POINTS: • High image quality bilateral breast MRI is achievable with clinical parameters at 7 T. • 7-T high-resolution imaging improves delineation of subtle soft tissue structures. • Adiabatic-based fat suppression provides excellent fibroglandular/fat contrast at 7 T. • 7- and 3-T 3D T1-weighted gradient-echo images have similar signal uniformity. • The 7-T dual solenoid coil enables bilateral imaging without compromising uniformity.

Comparison of the accuracy of PET/CT and PET/MRI spatial registration of multiple metastatic lesions.

OBJECTIVE: The purpose of this study was to compare the accuracy of the spatial registration of conventional PET/CT with that of hybrid PET/MRI of patients with FDG-avid metastatic lesions. SUBJECTS AND METHODS: Thirteen patients with known metastatic lesions underwent FDG PET/CT followed by PET/MRI with a hybrid whole-body system. The inclusion criterion for tumor analysis was spherical or oval FDG-avid tumor clearly identified with both CT and MRI. The spatial coordinates (x, y, z) of the visually estimated centers of the lesions were determined for PET/CT (PET and CT independently) and PET/MRI (PET, T1-weighted gradient-echo sequence with radial stack-of-stars trajectory, T2-weighted sequence), and the b0 images of an echo-planar imaging (EPI) diffusion-weighted imaging (DWI) acquisition. All MRI sequences were performed in the axial plane with free breathing. The spatial coordinates of the estimated centers of the lesions were determined for PET and CT and PET and MRI sequences. Distance between the isocenter of the lesion on PET images and on the images obtained with the anatomic modalities was measured, and misregistration (in millimeters) was calculated. The degree of misregistration was compared between PET/CT and PET/MRI with a paired Student t test. RESULTS: Nineteen lesions were evaluated. On PET/CT images, the average of the total misregistration in all planes of CT compared with PET was 4.13 ± 4.24 mm. On PET/MR images, lesion misregistration between PET and T1-weighted gradient-echo images had a shift of 2.41 ± 1.38 mm and between PET and b0 DW images was 5.97 ± 2.83 mm. Similar results were calculated for 11 lesions on T2-weighted images. The shift on T2-weighted images compared with PET images was 2.24 ± 1.12 mm. Paired Student t test calculations for PET/CT compared with PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory, b0 DW images, and T2-weighted images showed significant differences (p < 0.05). Similar results were seen in the analysis of six lung lesions. CONCLUSION: PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory and T2-weighted images had more accurate spatial registration than PET/CT images. This may be because that the whole-body PET/MRI system used can perform simultaneous acquisition, whereas the PET/CT system acquires data sequentially. However, the EPI-based b0 DWI datasets were significantly misregistered compared with the PET/CT datasets, especially in the thorax. Radiologists reading PET/MR images should be aware of the potential for misregistration on images obtained with EPI-based DWI sequences because of inherent spatial distortion associated with this type of MRI acquisition.

Correlation between standardized uptake value and apparent diffusion coefficient of neoplastic lesions evaluated with whole-body simultaneous hybrid PET/MRI.

OBJECTIVE: The purpose of this study was to assess the correlation between standardized uptake value (SUV) and apparent diffusion coefficient (ADC) of neoplastic lesions in the use of a simultaneous PET/MRI hybrid system. SUBJECTS AND METHODS: Twenty-four patients with known primary malignancies underwent FDG PET/CT. They then underwent whole-body PET/MRI. Diffusion-weighted imaging was performed with free breathing and a single-shot spin-echo echo-planar imaging sequence with b values of 0, 350, and 750 s/mm(2). Regions of interest were manually drawn along the contours of neoplastic lesions larger than 1 cm, which were clearly identified on PET and diffusion-weighted images. Maximum SUV (SUVmax) on PET/MRI and PET/CT images, mean SUV (SUVmean), minimum ADC (ADCmin), and mean ADC (ADCmean) were recorded on PET/MR images for each FDG-avid neoplastic soft-tissue lesion with a maximum of three lesions per patient. Pearson correlation coefficient was used to asses the following relations: SUVmax versus ADCmin on PET/MR and PET/CT images, SUVmean versus ADCmean, and ratio of SUVmax to mean liver SUV (SUV ratio) versus ADCmin. A subanalysis of patients with progressive disease versus partial treatment response was performed with the ratio of SUVmax to ADCmin for the most metabolically active lesion. RESULTS: Sixty-nine neoplastic lesions (52 nonosseous lesions, 17 bone metastatic lesions) were evaluated. The mean SUVmax from PET/MRI was 7.0 ± 6.0; SUVmean, 5.6 ± 4.6; mean ADCmin, 1.10 ± 0.58; and mean ADCmean, 1.48 ± 0.72. A significant inverse Pearson correlation coefficient was found between PET/MRI SUVmax and ADCmin (r = -0.21, p = 0.04), between SUVmean and ADCmean (r = -0.18, p = 0.07), and between SUV ratio and ADCmin (r = -0.27, p = 0.01). A similar inverse Pearson correlation coefficient was found between the PET/CT SUVmax and ADCmin. Twenty of 24 patients had previously undergone PET/CT; five patients had a partial treatment response, and six had progressive disease according to Response Evaluation Criteria in Solid Tumors 1.1. The ratio between SUVmax and ADCmin was higher among patients with progressive disease than those with a partial treatment response. CONCLUSION: Simultaneous PET/MRI is a promising technology for the detection of neoplastic disease. There are inverse correlations between SUVmax and ADCmin and between SUV ratio and ADCmin. Correlation coefficients between SUVmax and ADCmin from PET/MRI were similar to values obtained with SUVmax from the same-day PET/CT. Given that both SUV and ADC are related to malignancy and that the correlation between the two biomarkers is relatively weak, SUV and ADC values may offer complementary information to aid in determination of prognosis and treatment response. The combined tumoral biomarker, ratio between SUVmax and ADCmin, may be useful for assessing progressive disease versus partial treatment response.

3DMR osseous reconstructions of the shoulder using a gradient-echo based two-point Dixon reconstruction: a feasibility study.

OBJECTIVE: To create 3DMR osseous models of the shoulder similar to 3DCT models using a gradient-echo-based two-point/Dixon sequence. MATERIALS AND METHODS: CT and 3TMR examinations of 7 cadaveric shoulders were obtained. Glenoid defects were created in 4 of the cadaveric shoulders. Each MR study included an axial Dixon 3D-dual-echo-time T1W-FLASH (acquisition time of 3 min/30 s). The water-only image data from the Dixon sequence and CT data were post-processed using 3D software. The following measurements were obtained on the shoulders: surface area (SA), height/width of the glenoid and humeral head, and width of the biceps groove. The glenoid defects were measured on imaging and compared with measurements made on en face digital photographs of the glenoid fossae (reference standard). Paired t tests/ANOVA were used to assess the differences between the imaging modalities. RESULTS: The differences between the glenoid and humeral measurements were not statistically significant (cm): glenoid SA 0.12 ± 0.04 (p = 0.45) and glenoid width 0.13 ± 0.06 (p = 0.06) with no difference in glenoid height measurement; humeral head SA 0.07 ± 0.12 (p = 0.42), humeral head height 0.03 ± 0.06 (p = 0.42), humeral head width 0.07 ± 0.06(p = 0.18), and biceps groove width 0.02 ± 0.01 (p = 0.07). The mean/standard deviation difference between the reference standard and 3DMR measurements was 0.25 ± 0.96 %/0.30 ± 0.14 mm; 3DCT 0.25 ± 0.96 /0.75 ± 0.39 mm. There was no statistical difference between the measurements obtained on 3DMR and 3DCT (percentage, p = 0.45; mm, p = 0.20). CONCLUSION: Accurate 3D osseous models of the shoulder can be produced using a 3D two-point/Dixon sequence and can be added to MR examinations with a minor increase in imaging time, used to quantify glenoid loss, and may eliminate the need for pre-surgical CT examinations.

Introduction of Lazy Luna an automatic software-driven multilevel comparison of ventricular function quantification in cardiovascular magnetic resonance imaging.

Cardiovascular magnetic resonance imaging is the gold standard for cardiac function assessment. Quantification of clinical results (CR) requires precise segmentation. Clinicians statistically compare CRs to ensure reproducibility. Convolutional Neural Network developers compare their results via metrics. Aim: Introducing software capable of automatic multilevel comparison. A multilevel analysis covering segmentations and CRs builds on a generic software backend. Metrics and CRs are calculated with geometric accuracy. Segmentations and CRs are connected to track errors and their effects. An interactive GUI makes the software accessible to different users. The software's multilevel comparison was tested on a use case based on cardiac function assessment. The software shows good reader agreement in CRs and segmentation metrics (Dice > 90%). Decomposing differences by cardiac position revealed excellent agreement in midventricular slices: > 90% but poorer segmentations in apical (> 71%) and basal slices (> 74%). Further decomposition by contour type locates the largest millilitre differences in the basal right cavity (> 3 ml). Visual inspection shows these differences being caused by different basal slice choices. The software illuminated reader differences on several levels. Producing spreadsheets and figures concerning metric values and CR differences was automated. A multilevel reader comparison is feasible and extendable to other cardiac structures in the future.

Improving robustness of automatic cardiac function quantification from cine magnetic resonance imaging using synthetic image data.

Although having been the subject of intense research over the years, cardiac function quantification from MRI is still not a fully automatic process in the clinical practice. This is partly due to the shortage of training data covering all relevant cardiovascular disease phenotypes. We propose to synthetically generate short axis CINE MRI using a generative adversarial model to expand the available data sets that consist of predominantly healthy subjects to include more cases with reduced ejection fraction. We introduce a deep learning convolutional neural network (CNN) to predict the end-diastolic volume, end-systolic volume, and implicitly the ejection fraction from cardiac MRI without explicit segmentation. The left ventricle volume predictions were compared to the ground truth values, showing superior accuracy compared to state-of-the-art segmentation methods. We show that using synthetic data generated for pre-training a CNN significantly improves the prediction compared to only using the limited amount of available data, when the training set is imbalanced.

Resolving arterial phase and temporal enhancement characteristics in DCE MRM at high spatial resolution with TWIST acquisition.

PURPOSE: To investigate the potential of a view-sharing 3D fast gradient-echo sequence using pseudo random trajectories (TWIST) to achieve very short acquisition times with high in-plane resolution and good volume coverage and its application to dynamic contrast-enhanced (DCE) breast magnetic resonance imaging (MRI). MATERIALS AND METHODS: Two versions of a 3D fast gradient echo TWIST sequence were implemented and applied to patients: First, an ultrafast TWIST acquisition (TA = 5.7 sec) in combination with a routine DCE MRM protocol to allow the extraction of arterial input functions and to resolve the first pass of the contrast agent. Second, a dynamic full coverage TWIST DCE acquisition (TA = 10.6 sec) in a repeat examination, replacing the routine DCE MRM sequence. RESULTS: The ultrafast acquisition enabled extraction of arterial input functions and the monitoring of the contrast agent's first pass through vessels and lesions. The dynamic full coverage TWIST acquisition captured the initial dynamic slope of the signal time curve of lesions accurately, in contrast to the routine protocol. CONCLUSION: TWIST acquisitions proved very robust and offer high flexibility in protocol timing. The ultrafast protocol achieved 5.7 seconds time resolution with good image quality and can be combined with any established routine protocol. The full dynamics TWIST DCE protocol offers improved time resolution of the CE dynamic time-course and closely matches the image quality of the routine protocol.

Evaluation of 4D flow MRI-based non-invasive pressure assessment in aortic coarctations.

Severity of aortic coarctation (CoA) is currently assessed by estimating trans-coarctation pressure drops through cardiac catheterization or echocardiography. In principle, more detailed information could be obtained non-invasively based on space- and time-resolved magnetic resonance imaging (4D flow) data. Yet the limitations of this imaging technique require testing the accuracy of 4D flow-derived hemodynamic quantities against other methodologies. With the objective of assessing the feasibility and accuracy of this non-invasive method to support the clinical diagnosis of CoA, we developed an algorithm (4DF-FEPPE) to obtain relative pressure distributions from 4D flow data by solving the Poisson pressure equation. 4DF-FEPPE was tested against results from a patient-specific fluid-structure interaction (FSI) simulation, whose patient-specific boundary conditions were prescribed based on 4D flow data. Since numerical simulations provide noise-free pressure fields on fine spatial and temporal scales, our analysis allowed to assess the uncertainties related to 4D flow noise and limited resolution. 4DF-FEPPE and FSI results were compared on a series of cross-sections along the aorta. Bland-Altman analysis revealed very good agreement between the two methodologies in terms of instantaneous data at peak systole, end-diastole and time-averaged values: biases (means of differences) were +0.4 mmHg, -1.1 mmHg and +0.6 mmHg, respectively. Limits of agreement (2 SD) were ±0.978 mmHg, ±1.06 mmHg and ±1.97 mmHg, respectively. Peak-to-peak and maximum trans-coarctation pressure drops obtained with 4DF-FEPPE differed from FSI results by 0.75 mmHg and -1.34 mmHg respectively. The present study considers important validation aspects of non-invasive pressure difference estimation based on 4D flow MRI, showing the potential of this technology to be more broadly applied to the clinical practice.

Diffusion weighted imaging in breast MRI: comparison of two different pulse sequences.

RATIONALE AND OBJECTIVES: Comparison of two different diffusion weighted (DW) sequences in breast MRI regarding the differentiation between benign and malignant lesions. MATERIALS AND METHODS: Breast MRI including two different DW sequences was performed in 165 consecutive women. Inclusion criteria for DW imaging and ADC evaluation were histologically proven focal mass lesions with a diameter of more than 5 mm in dynamic contrast-enhanced MRI. The DW sequences were pre-contrast echo-planar imaging with spectral fat saturation (EPI fs) and DW EPI with inversion recovery (EPI STIR) (b-values: 50, 400, and 800). Lesions were analyzed regarding visibility in DW sequences and ADC values. RESULTS: Inclusion criteria were fulfilled in 56 women with 69 lesions. Five lesions could not be evaluated for different reasons. Finally, DW sequences were evaluated in 51 women with 64 focal mass lesions (15 benign, 49 malignant). The visibility of the lesions was significantly better in the EPI fs sequence (P<0.05). The ADC values (10(-3) mm(2)/s) in the EPI fs were 1.76, 2.58, and 1.21 (mean, maximum, minimum, respectively) for benign lesions and 0.90, 1.19, and 0.34 for malignant lesions. Respective values in the EPI STIR sequence were 1.92, 3.20, 1.10, and 0.91, 1.43, 0.35. Only in the EPI fs sequence there was no overlap in ADC values between benign and malignant lesions. CONCLUSION: The DW MRI of the breast with EPI fs and EPI STIR sequences has a high potential to differentiate between benign and malignant breast lesions. Due to better lesion visibility and selectivity, the EPI fs sequence should be preferred.