Clinical Feasibility of Synthetic Magnetic Resonance Imaging in the Diagnosis of Internal Derangements of the Knee

Potential clinical feasibility of synthetic MRI in bladder tumors: a comparative study with conventional MRI

Background

Synthetic magnetic resonance imaging (MRI) can provide quantitative information about inherent tissue properties and synthesize tailored contrast-weighted images simultaneously in a single scan. This study aimed to investigate the clinical feasibility of synthetic MRI in bladder tumors.

Methods

A total of 47 patients (37 males; mean age: 66±10 years old) with postoperative pathology-confirmed papillary urothelial neoplasms of the bladder were enrolled in this retrospective study. A 2-dimensional (2D) multi-dynamic multi-echo pulse sequence was performed for synthetic MRI at 3T. The overall image quality, lesion conspicuity, contrast resolution, resolution of subtle anatomic structures, motion artifact, blurring, and graininess of images were subjectively evaluated by 2 radiologists independently using a 5-point Likert scale for qualitative analysis. The signal intensity ratio (SIR), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured for quantitative analysis. Linear weighted Kappa, Wilcoxon's signed-rank test, and the Mann-Whitney U-test were used for statistical analysis.

Results

The interobserver consistency was excellent (κ values: 0.607-1). Synthetic T1-weighted (syn-T1w) and synthetic T2-weighted (syn-T2w) images obtained scores of 4 in most subjective terms, which were relatively smaller than those of conventional images. The SIR and SNR of syn-T1w were significantly higher than those of con-T1w images (SIR 2.37±0.86 vs. 1.47±0.20, P<0.001; SNR 21.83±9.43 vs. 14.81±3.30, P<0.001). No difference was found in SIR between syn-T2w and conventional T2-weighted (con-T2w) images, whereas the SNR of the syn-T2w was significantly lower (8.79±4.06 vs. 26.49±6.80, P<0.001). Additionally, the CNR of synthetic images was significantly lower than that of conventional images (T1w 1.41±0.72 vs. 2.68±1.04; T2w 1.40±0.87 vs. 4.03±1.55, all P<0.001).

Conclusions

Synthetic MRI generates morphologic magnetic resonance (MR) images with diagnostically acceptable image quality in bladder tumors, especially T1-weighted images with high image contrast of tumors relative to urine. Further technological improvements are needed for synthetic MRI to reduce noise. Combined with T1, T2, and proton density (PD) quantitative data, synthetic MRI has potential for clinical application in bladder tumors.

Image quality using synthetic brain MRI: an age-stratified study

BACKGROUND

Synthetic magnetic resonance imaging (MRI) might replace the conventional MR sequences in brain evaluation to shorten scan time and obtain multiple quantitative parameters.

PURPOSE

To evaluate the image quality of multiple-delay-multiple-echo (MDME) sequence-derived synthetic brain MR images compared to conventional images by considering a multi-age sample.

MATERIAL AND METHODS

Image sets of conventional and synthetic MRI of 200 participants were included. On the basis of the presence of intracranial lesions, the participants were divided into a normal group and a pathological group. Two neuroradiologists compared the anonymous and unordered images. Image quality, artifacts, and diagnostic performance were analyzed.

RESULTS

In the quantitative analysis, comparing with conventional images, MDME sequence-derived synthetic MRI demonstrated an equal/greater signal-to-noise ratio and contrast-to-noise ratio (CNR) in all age groups. Specifically, for participants aged ≤2 years, synthetic T2-fluid-attenuated inversion recovery imaging showed a significantly higher cerebellum gray/white matter CNR (P < 0.05). In the qualitative and artifact analyses, except for the superior sagittal sinus and cranial nerves, synthetic MRI showed good imaging quality (≥3 points) in all brain structures. On synthetic T1-weighted imaging, high signal intensity within the superior sagittal sinus was found in most of our participants (107/118, 90.7%). No difference was observed between synthetic and conventional MRI in diagnosing the lesions.

CONCLUSION

MDME sequence-derived synthetic MRI showed similar image quality and diagnostic performance with a shorter acquisition time than conventional MRI. However, the high signal intensity within the superior sagittal sinus on synthetic T1-weighted images requires consideration.

Synthetic Contrasts in Musculoskeletal MRI: A Review

ABSTRACT

This review summarizes the existing techniques and methods used to generate synthetic contrasts from magnetic resonance imaging data focusing on musculoskeletal magnetic resonance imaging. To that end, the different approaches were categorized into 3 different methodological groups: mathematical image transformation, physics-based, and data-driven approaches. Each group is characterized, followed by examples and a brief overview of their clinical validation, if present. Finally, we will discuss the advantages, disadvantages, and caveats of synthetic contrasts, focusing on the preservation of image information, validation, and aspects of the clinical workflow.

The effect of scan parameters on T1, T2 relaxation times measured with multi-dynamic multi-echo sequence: a phantom study

Multi-Dynamic Multi-Echo (MDME) Sequence is a new method which can acquire various contrast-weighted images using quantitative relaxometric parameters measured from multicontrast images. The purpose of our study was to investigate the effect of scan parameters of MDME Sequence on measured T1, T2 values of phantoms at 3.0 T MRI scanner. Gray matter, white matter and cerebrospinal fluid simulation phantoms with different relaxation times (named GM, WM, CSF, respectively) were used in our study. All the phantoms were scanned 9 times on different days using MDME sequence with variations of echo train length, matrix, and acceleration factor. The T1, T2 measurements were acquired after each acquisition. The repeatability was characterized as the intragroup coefficient of variation (CV) of measured values over 9 times, and the discrepancies of measurements across different groups were characterized as intergroup CVs. The highest intragroup CVs of T1-GM, T2-GM, T1-WM, T2-WM, T1-CSF, T2-SCF were 1.36%, 1.75%, 0.74%, 1.41%, 1.70%, 7.79%, respectively. The highest intergroup CVs of T1-GM, T2-GM, T1-WM, T2-WM, T1-CSF, T2-SCF were 0.54%, 1.86%, 1.70%, 0.94%, 1.00%, 2.17%, respectively. Quantitative T1, T2 measurements of gray matter, white matter and cerebrospinal fluid simulation phantoms derived from the MDME sequence were not obviously affected by variations of scanning parameters, such as echo train length, matrix, and acceleration factor on 3T scanner.

Synthetic magnetic resonance imaging for primary prostate cancer evaluation: Diagnostic potential of a non-contrast-enhanced bi-parametric approach enhanced with relaxometry measurements

Purpose

Bi-parametric magnetic resonance imaging (bpMRI) with diffusion-weighted images has wide utility in diagnosing clinically significant prostate cancer (csPCa). However, bpMRI yields more false-negatives for PI-RADS category 3 lesions than multiparametric (mp)MRI with dynamic-contrast-enhanced (DCE)-MRI. We investigated the utility of synthetic MRI with relaxometry maps for bpMRI-based diagnosis of csPCa.

Methods

One hundred and five treatment-naïve patients who underwent mpMRI and synthetic MRI before prostate biopsy for suspected PCa between August 2019 and December 2020 were prospectively included. Three experts and three basic prostate radiologists evaluated the diagnostic performance of conventional bpMRI and synthetic bpMRI for csPCa. PI-RADS version 2.1 category 3 lesions were identified by consensus, and relaxometry measurements (T1-value, T2-value, and proton density [PD]) were performed. The diagnostic performance of relaxometry measurements for PI-RADS category 3 lesions in peripheral zone was compared with that of DCE-MRI. Histopathological evaluation results were used as the reference standard. Statistical analysis was performed using the areas under the receiver operating characteristic curve (AUC) and McNemar test.

Results

In 102 patients without significant MRI artefacts, the diagnostic performance of conventional bpMRI was not significantly different from that of synthetic bpMRI for all readers (p = 0.11–0.79). The AUCs of the combination of T1-value, T2-value, and PD (T1 + T2 + PD) for csPCa in peripheral zone for PI-RADS category 3 lesions were 0.85 for expert and 0.86 for basic radiologists, with no significant difference between T1 + T2 + PD and DCE-MRI for both expert and basic radiologists (p = 0.29–0.45).

Conclusion

Synthetic MRI with relaxometry maps shows promise for contrast media-free evaluation of csPCa.

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Diagnostic performances of synthetic bpMRI and conventional bpMRI are comparable for primary PCa

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Diagnostic performance of synthetic MRI variables are similar to that of DCE-MRI for csPCa in PZ

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Synthetic bpMRI shows potential as a contrast agent-free method for primary PCa

Clinical feasibility of simultaneous multislice acceleration in knee MRI

PURPOSE

To find the best simultaneous multislice (SMS) accelerated setting for clinical application in knee MRI.

MATERIAL AND METHODS

Thirty-three patients (mean age, 54 years; 21 women) who underwent knee MRI (conventional/SMS sequences) between June and October 2020 were enrolled. Two radiologists retrospectively evaluated sagittal T1- and T2-weighted conventional (2-fold parallel acquisition technique [PAT-2]) and SMS (SMS-2 [PAT-2 with 2-fold SMS], SMS-3, and SMS-4) images. For qualitative analysis, artifacts (zebra/residual aliasing) and diagnostic confidence for internal derangement of knee (bone marrow, cartilage, meniscus, anterior cruciate ligament, and synovium abnormalities) were evaluated. For quantitative analysis, contrast-to-noise ratios of bone marrow, meniscus, joint effusion, and ligament were evaluated.

RESULTS

Compared to PAT-2 (2 min 32 s), mean acquisition time was reduced by 47% in SMS-2; 64%, SMS-3; and 70%, SMS-4. In qualitative analysis, zebra artifacts were only seen on T2-weighted SMS images. The more SMS was applied, the more zebra and residual aliasing artifacts were seen and the lower diagnostic confidence was for internal derangement. However, qualitative analysis showed acceptable image quality in SMS-2 and SMS-3 images, but not in SMS-4 images. In quantitative analysis, SMS-4 images showed the lowest contrast-to-noise ratios and there were no significant differences among PAT-2, SMS-2, and SMS-3 images.

CONCLUSION

Applying SMS-3 to knee MRI reduced scan time and showed acceptable image quality compared to conventional (PAT-2). However, when evaluating SMS images, radiologists should know that when more SMS is applied, more zebra and residual aliasing artifacts appear.

Deep Generative Adversarial Networks: Applications in Musculoskeletal Imaging

In recent years, deep learning techniques have been applied in musculoskeletal radiology to increase the diagnostic potential of acquired images. Generative adversarial networks (GANs), which are deep neural networks that can generate or transform images, have the potential to aid in faster imaging by generating images with a high level of realism across multiple contrast and modalities from existing imaging protocols. This review introduces the key architectures of GANs as well as their technical background and challenges. Key research trends are highlighted, including: (a) reconstruction of high-resolution MRI; (b) image synthesis with different modalities and contrasts; (c) image enhancement that efficiently preserves high-frequency information suitable for human interpretation; (d) pixel-level segmentation with annotation sharing between domains; and (e) applications to different musculoskeletal anatomies. In addition, an overview is provided of the key issues wherein clinical applicability is challenging to capture with conventional performance metrics and expert evaluation. When clinically validated, GANs have the potential to improve musculoskeletal imaging. Keywords: Adults and Pediatrics, Computer Aided Diagnosis (CAD), Computer Applications-General (Informatics), Informatics, Skeletal-Appendicular, Skeletal-Axial, Soft Tissues/Skin © RSNA, 2021.

Investigating the Image Quality and Utility of Synthetic MRI in the Breast

Purpose

Synthetic MRI reconstructs multiple sequences in a single acquisition. In the present study, we aimed to compare the image quality and utility of synthetic MRI with that of conventional MRI in the breast.

Methods

We retrospectively collected the imaging data of 37 women (mean age: 55.1 years; range: 20–78 years) who had undergone both synthetic and conventional MRI of T2-weighted, T1-weighted, and fat-suppressed (FS)-T2-weighted images. Two independent breast radiologists evaluated the overall image quality, anatomical sharpness, contrast between tissues, image homogeneity, and presence of artifacts of synthetic and conventional MRI on a 5-point scale (5 = very good to 1 = very poor). The interobserver agreement between the radiologists was evaluated using weighted kappa.

Results

For synthetic MRI, the acquisition time was 3 min 28 s. On the 5-point scale evaluation of overall image quality, although the scores of synthetic FS-T2-weighted images (4.01 ± 0.56) were lower than that of conventional images (4.95 ± 0.23; P < 0.001), the scores of synthetic T1- and T2-weighted images (4.95 ± 0.23 and 4.97 ± 0.16) were comparable with those of conventional images (4.92 ± 0.27 and 4.97 ± 0.16; P = 0.484 and 1.000, respectively). The kappa coefficient of conventional MRI was fair (0.53; P < 0.001), and that of conventional MRI was fair (0.46; P < 0.001).

Conclusion

The image quality of synthetic T1- and T2-weighted images was similar to that of conventional images and diagnostically acceptable, whereas the quality of synthetic T2-weighted FS images was inferior to conventional images. Although synthetic MRI images of the breast have the potential to provide efficient image diagnosis, further validation and improvement are required for clinical application.

The diagnostic performance of quantitative mapping in breast cancer patients: a preliminary study using synthetic MRI

Background

Previous studies have indicated that quantitative MRI (qMR) is beneficial for diagnosis of breast cancer. As a novel qMR technology, synthetic MRI (syMRI) may be advantageous by offering simultaneous generation of T1 and T2 mapping in one scan within a few minutes and without concern to the deposition of the gadolinium contrast agent in cell nucleus. In this study, the potential of quantitative mapping derived from Synthetic MRI (SyMRI) to diagnose breast cancer was investigated.

Methods

From April 2018 to May 2019, a total of 87 patients with suspicious breast lesions underwent both conventional and SyMRI before treatment. The quantitative metrics derived from SyMRI, including T1 and T2 values, were measured in breast lesions. The diagnostic performance of SyMRI was evaluated with unpaired Student’s t-tests, receiver operating characteristic curve analysis and multivariate logistic regression analysis. The AUCs of quantitative values were compared using Delong test.

Results

Among 77 patients who met the inclusion criteria, 48 were diagnosed with histopathological confirmed breast cancers, and the rest had benign lesions. The breast cancers showed significantly higher T1 (1611.61 ± 215.88 ms) values and lower T2 (80.93 ± 7.51 ms) values than benign lesions. The area under the ROC curve (AUC) values were 0.931 (95% CI: 0.874–0.989) and 0.883 (95% CI: 0.810–0.956) for T1 and T2 maps, respectively, in diagnostic discrimination between breast cancers and benign lesions. A slightly increased AUC of 0.978 (95% CI: 0.915–0.993) was achieved by combining those two relaxation-based quantitative metrics.

Conclusion

In conclusion, our preliminary study showed that the quantitative T1 and T2 values obtained by SyMRI could distinguish effectively between benign and malignant breast lesions, and T1 relaxation time showed the highest diagnostic efficiency. Furthermore, combining the two quantitative relaxation metrics further improved their diagnostic performance.

Synthetic MRI is not yet ready for morphologic and functional assessment of patellar cartilage at 1.5Tesla

PURPOSE

The purpose of this study was to compare morphologic assessment and relaxometry of patellar hyaline cartilage between conventional sequences (fast spin-echo [FSE] T2-weighted fat-saturated and T2-mapping) and synthetic T2 short-TI inversion recovery (STIR) and T2 maps at 1.5T magnetic resonance imaging (MRI).

METHOD

The MRI examinations of the knee obtained at 1.5T in 49 consecutive patients were retrospectively studied. There were 21 men and 28 women with a mean age of 45±17.7 (SD) years (range: 18-88 years). Conventional and synthetic acquisitions were performed, including T2-weighted fat-saturated and T2-mapping sequences. Two radiologists independently compared patellar cartilage T2-relaxation time on conventional T2-mapping and synthetic T2-mapping images. A third radiologist evaluated the patellar cartilage morphology on conventional and synthetic T2-weighted images. The presence of artifacts was also assessed. Interobserver agreement for quantitative variables was assessed using intraclass correlation coefficient (ICC).

RESULTS

In vitro, conventional and synthetic T2 maps yielded similar mean T2 values 58.5±2.3 (SD) ms and 58.8±2.6 (SD) ms, respectively (P=0.414) and 6% lower than the expected experimental values (P=0.038). Synthetic images allowed for a 15% reduction in examination time compared to conventional images. On conventional sequences, patellar chondropathy was identified in 35 patients (35/49; 71%) with a mean chondropathy grade of 4.8±4.8 (SD). On synthetic images, 28 patients (28/49; 57%) were diagnosed with patellar chondropathy, with a significant 14% difference (P=0.009) and lower chondropathy scores (3.7±4.9 [SD]) compared to conventional images. Motion artifacts were more frequently observed on synthetic images (18%) than on conventional ones (6%). The interobserver agreement was excellent for both conventional and synthetic T2 maps (ICC>0.83). Mean cartilage T2 values were significantly greater on synthetic images (36.2±3.8 [SD] ms; range: 29-46ms) relative to conventional T2 maps (31.8±4.1 [SD] ms; range: 26-49ms) (P<0.0001).

CONCLUSION

Despite a decrease in examination duration, synthetic images convey lower diagnostic performance for chondropathy, greater prevalence of motion artifacts, and an overestimation of T2 values compared to conventional MRI sequences.

Quantitative Assessment of Bone Metastasis in Prostate Cancer Using Synthetic Magnetic Resonance Imaging

OBJECTIVES

The aims of this study were to evaluate the feasibility of quantitative synthetic magnetic resonance imaging (SyMRI) for characterizing bone lesions in prostate cancer and to discriminate viable progressive osteoblastic bone metastasis from nonviable bone metastases with treatment-induced sclerosis during the treatment course.

MATERIALS AND METHODS

This institutional review board-approved prospective study included 96 consecutive prostate cancer patients who underwent whole-body MRI including diffusion-weighted imaging at the time of staging at diagnosis or starting a new line of anticancer treatment. Additional synthetic MRI of the lumbosacral spine, pelvis, and proximal femurs was performed. A region of interest of 1.0 cm in diameter was set in each bone lesion by 2 independent readers who were blinded to bone lesions' diagnosis. Differences in SyMRI variables between the different bone lesions were compared with the Wilcoxon rank sum test, and associations of SyMRI variables with active disease were analyzed with logistic regression analysis. Performance of T1, T2, and proton density (PD) for diagnosing active disease was assessed using the area under the receiver operating characteristic curve.

RESULTS

Ninety-three bone lesions were eligible for analysis. The PD values of active (viable) bone metastatic lesions were significantly higher than those of inactive (nonviable) bone metastatic lesions without sclerosis and those of red bone marrow (P < 0.001 for both readers). The PD values of inactive bone metastatic lesions with sclerosis were significantly lower than those of inactive bone metastatic lesions without sclerosis and red bone marrow (P < 0.001 for both readers). The PD value proved to be an independent significant indicator (P < 0.001) for differentiating bone lesions. The areas under the curve of T1/T2/PD for identifying active disease were 0.81/0.69/0.93 for reader 1 and 0.78/0.70/0.92 for reader 2, respectively.

CONCLUSIONS

Signal quantification on SyMRI provides objective assessment of bone lesions in the lower trunk. The PD value can be useful to determine the viability of bone metastases in prostate cancer.

The feasibility of synthetic MRI in breast cancer patients: comparison of T2 relaxation time with multiecho spin echo T2 mapping method

OBJECTIVE

To compare the T2 relaxation times acquired with synthetic MRI to those of multi-echo spin-echo sequences and to evaluate the usefulness of synthetic MRI in the clinical setting.

METHODS

From January 2017 to May 2017, we included 51 patients with newly diagnosed breast cancer, who underwent additional synthetic MRI and multiecho spin echo (MESE) T2 mapping sequences. Synthetic MRI technique uses a multiecho and multidelay acquisition method for the simultaneous quantification of physical properties such as T1 and T2 relaxation times and proton density image map. A radiologist with 9 years of experience in breast imaging drew region of interests manually along the tumor margins on two consecutive axial sections including the center of tumor mass and in the fat tissue of contralateral breast on both synthetic T2 map and MESE T2 map images.

RESULTS

The mean T2 relaxation time of the cancer was 84.75 ms (± 15.54) by synthetic MRI and 90.35 ms (± 19.22) by MESE T2 mapping. The mean T2 relaxation time of the fat was 129.22 ms (± 9.53) and 102.11 ms (± 13.9), respectively. Bland-Altman analysis showed mean difference of 8.4 ms for the breast cancer and a larger mean difference of 27.8 ms for the fat tissue. Spearman's correlation test showed that there was significant positive correlation between synthetic MRI and MESE sequences for the cancer (r = 0.713, p < 0.001) and for the fat (r = 0.551, p < 0.001). The positive estrogen receptor and low histologic grade were associated with little differences between two methods (p = 0.02  and = 0.043, respectively).

CONCLUSION

T2 relaxation times of breast cancer acquired with synthetic MRI showed positive correlation with those of MESE T2 mapping. Synthetic MRI could be useful for the evaluation of tissue characteristics by simultaneous acquisition of several quantitative physical properties.

ADVANCES IN KNOWLEDGE

Synthetic MRI is useful for the evaluation of T2 relaxation times of the breast cancers.

Feasibility of a Synthetic MR Imaging Sequence for Spine Imaging

BACKGROUND AND PURPOSE

Synthetic MR imaging is a method that can produce multiple contrasts from a single sequence, as well as quantitative maps. Our aim was to determine the feasibility of a synthetic MR image for spine imaging.

MATERIALS AND METHODS

Thirty-eight patients with clinical indications of infectious, degenerative, and neoplastic disease underwent an MR imaging of the spine (11 cervical, 8 dorsal, and 19 lumbosacral MR imaging studies). The SyntAc sequence, with an acquisition time of 5 minutes 40 seconds, was added to the usual imaging protocol consisting of conventional sagittal T1 TSE, T2 TSE, and STIR TSE.

RESULTS

Synthetic T1-weighted, T2-weighted, and STIR images were of adequate quality, and the acquisition time was 53% less than with conventional MR imaging. The image quality was rated as "good" for both synthetic and conventional images. Interreader agreement concerning lesion conspicuity was good with a Cohen κ of 0.737. Artifacts consisting of white pixels/spike noise across contrast views, as well as flow artifacts, were more common in the synthetic sequences, particularly in synthetic STIR. There were no statistically significant differences between readers concerning the scores assigned for image quality or lesion conspicuity.

CONCLUSIONS

Our study shows that synthetic MR imaging is feasible in spine imaging and produces, in general, good image quality and diagnostic confidence. Furthermore, the non-negligible time savings and the ability to obtain quantitative measurements as well as to generate several contrasts with a single acquisition should promise a bright future for synthetic MR imaging in clinical routine.