T2-weighted Turbo Spin-echo Magnetic Resonance Imaging Research Articles

Deep cross-modality (MR-CT) educed distillation learning for cone beam CT lung tumor segmentation.

Despite the widespread availability of in-treatment room cone beam computed tomography (CBCT) imaging, due to the lack of reliable segmentation methods, CBCT is only used for gross set up corrections in lung radiotherapies. Accurate and reliable auto-segmentation tools could potentiate volumetric response assessment and geometry-guided adaptive radiation therapies. Therefore, we developed a new deep learning CBCT lung tumor segmentation method. The key idea of our approach called cross-modality educed distillation (CMEDL) is to use magnetic resonance imaging (MRI) to guide a CBCT segmentation network training to extract more informative features during training. We accomplish this by training an end-to-end network comprised of unpaired domain adaptation (UDA) and cross-domain segmentation distillation networks (SDNs) using unpaired CBCT and MRI datasets. UDA approach uses CBCT and MRI that are not aligned and may arise from different sets of patients. The UDA network synthesizes pseudo MRI from CBCT images. The SDN consists of teacher MRI and student CBCT segmentation networks. Feature distillation regularizes the student network to extract CBCT features that match the statistical distribution of MRI features extracted by the teacher network and obtain better differentiation of tumor from background. The UDA network was implemented with a cycleGAN improved with contextual losses separately on Unet and dense fully convolutional segmentation networks (DenseFCN). Performance comparisons were done against CBCT only using 2D and 3D networks. We also compared against an alternative framework that used UDA with MR segmentation network, whereby segmentation was done on the synthesized pseudo MRI representation. All networks were trained with 216 weekly CBCTs and 82 T2-weighted turbo spin echo MRI acquired from different patient cohorts. Validation was done on 20 weekly CBCTs from patients not used in training. Independent testing was done on 38 weekly CBCTs from patients not used in training or validation. Segmentation accuracy was measured using surface Dice similarity coefficient (SDSC) and Hausdroff distance at 95th percentile (HD95) metrics. The CMEDL approach significantly improved (p < 0.001) the accuracy of both Unet (SDSC of 0.83±0.08; HD95 of 7.69±7.86mm) and DenseFCN (SDSC of 0.75±0.13; HD95 of 11.42±9.87mm) over CBCT only 2DUnet (SDSC of 0.69±0.11; HD95 of 21.70±16.34mm), 3D Unet (SDSC of 0.72±0.20; HD95 15.01±12.98mm), and DenseFCN (SDSC of 0.66±0.15; HD95 of 22.15±17.19mm) networks. The alternate framework using UDA with the MRI network was also more accurate than the CBCT only methods but less accurate the CMEDL approach. Our results demonstrate feasibility of the introduced CMEDL approach to produce reasonably accurate lung cancer segmentation from CBCT images. Further validation on larger datasets is necessary for clinical translation.

Efficient segmentation of lumbar intervertebral disc from MR images

Segmentation of spine Magnetic Resonance Images (MRIs) has become an indispensable process in the diagnosis of lumbar disc degeneration, causing low back pain. Over the last decade of years, computer-directed diagnosis of disease, as well as computer-guided spine surgery, is based on the two-dimensional (2D) analysis of mid-sagittal slice of MRI. This work proposes an automatic strategy to extract the 3D segmentation of the normal disc as well as degenerated lumbar intervertebral discs (IVDs) from T2-weighted Turbo Spin Echo MRI of the spine using Connected Component (CC) analysis algorithm and statistical shape analysis. The challenges faced by the IVD segmentation includes (i) partial volume effects (ii) intensity inhomogeneity (iii) grey level overlap of different soft tissues. The proposed method first pre-processes the dataset and enables it for the application of the CC algorithm. The CC (subsets of pixels of the disc) of the spine MRI is extracted and apply statistical shape analysis for the refinement of the segmentation results to detect IVDs. Experimental results of the proposed method show a robust segmentation, accomplishing the dice similarity index of 92.4% and thus achieving a low error rate. Other performance measures such as Precision, Accuracy, JaccardIdx, JaccardDist, Global Consistency Error, Variation of Information, etc were also evaluated. The algorithm is evaluated quantitatively using adequate experiments on a dataset of 15 MRI scans, of different scenarios such as healthy and degenerate disc and this proposed method is verified as a promising accurate method for the automatic segmentation of IVD.

Quantitative characterization of optic nerve atrophy in patients with multiple sclerosis.

BackgroundOptic neuritis (ON) is one of the most common presentations of multiple sclerosis (MS). Magnetic resonance imaging (MRI) of the optic nerves is challenging because of retrobulbar motion, orbital fat and susceptibility artifacts from maxillary sinuses; therefore, axonal loss is investigated with the surrogate measure of a single heuristically defined point along the nerve as opposed to volumetric investigation.ObjectiveThe objective of this paper is to derive optic nerve volumetrics along the entire nerve length in patients with MS and healthy controls in vivo using high-resolution, clinically viable MRI.MethodsAn advanced, isotropic T2-weighted turbo spin echo MRI was applied to 29 MS patients with (14 patients ON+) or without (15 patients ON–) history of ON and 42 healthy volunteers. An automated tool was used to estimate and compare whole optic nerve and surrounding cerebrospinal fluid radii along the length of the nerve.Results and conclusionOnly ON+ MS patients had a significantly reduced optic nerve radius compared to healthy controls in the central segment of the optic nerve. Using clinically available MRI methods, we show and quantify ON volume loss for the first time in MS patients.

Localized Hyperthermia with Iron Oxide–Doped Yttrium Microparticles: Steps toward Image-Guided Thermoradiotherapy in Liver Cancer

PurposeTo test whether iron oxide (IO)–containing yttrium aluminosilicate (YAS) microparticles (MPs) can generate localized therapeutic hyperthermia (≥ 43°C) when injected intratumorally in an animal model of liver cancer and whether MP distributions could be visualized with magnetic resonance (MR) imaging. Materials and MethodsTwenty-one Sprague–Dawley rats implanted with N1-S1 liver tumors were assigned to alternating magnetic field (AMF) exposure following intratumoral injection with IO-YAS MPs (n = 7), sham surgery (n = 7), or baseline iron quantification (n = 7). Three fiberoptic probes allowed spatial and temporal monitoring of temperatures during 24 minutes of AMF exposure. T2-weighted turbo spin-echo MR imaging was performed within 1 hour after the procedure to detect signal voids caused by IO-YAS deposition. Hematoxylin and eosin–stained pathologic slides were also obtained, and the presence of IO-YAS was evaluated with inductively coupled plasma optical emission spectroscopy. ResultsFollowing AMF exposure, intratumoral temperatures after IO-YAS MP injection achieved therapeutic hyperthermia whereas those after sham surgery did not (46.6°C ± 1.3 vs 36.8°C ± 0.4; P < .0001). Within the treated group, the normal hepatic parenchyma (NHP) and rectal temperatures were 37.4°C ± 0.9 and 36.5°C ± 1.0 (P = .0809) at the conclusion of AMF exposure, respectively. A T2-weighted signal void at the tumor site was observed in all seven treated animals, and intratumoral IO-YAS was visualized on subsequent histopathologic examination in each case. The mean ratio of tumor:NHP Fe concentrations attributable to IO-YAS MPs was 108:1. ConclusionsAMF exposure of intratumoral IO-YAS MPs generates localized therapeutic hyperthermia in an animal model of liver cancer. MR detectability and potential for combination brachytherapy warrants further investigation for thermoradiotherapy in liver cancer.

Uterine Tumors: Comparison of 3D versus 2D T2-weighted Turbo Spin-Echo MR Imaging at 3.0 T—Initial Experience

To compare a three-dimensional (3D) T2-weighted turbo spin-echo (TSE) magnetic resonance (MR) sequence (VISTA; Philips Medical Systems, Best, the Netherlands) with a two-dimensional (2D) T2-weighted TSE sequence in terms of image quality, signal intensity (SI) difference ratios, conspicuity, and staging of uterine tumors. This retrospective study was approved by the institutional review board, and informed consent was waived. Sixty-one women (mean age, 53.0 years ± 13.7 [standard deviation]; range, 30-87 years) with cervical carcinoma (n = 28), endometrial carcinoma (n = 21), or leiomyoma (n = 30) of the uterus were included. Patients underwent T2-weighted MR imaging at 3 T with both 1-mm-thick 3D and 5-mm-thick 2D T2-weighted TSE sequences. Three-dimensional T2-weighted TSE images were reconstructed at 5-mm thickness with the aid of a workstation. Quantitative analyses of signal-to-noise ratio (SNR) and SI difference ratios between tumors and other tissues and qualitative analyses of image quality and tissue conspicuity were performed. Two radiologists independently assessed local-regional staging for carcinomas. Quantitative values, qualitative scores, and tumor staging were analyzed by using the paired t test, Wilcoxon signed rank test, and McNemar test, respectively. Mean myometrial SNR was higher on 3D than 2D images (14.3 vs 9.8; P < .0001). Mean SI difference ratios between cervical (0.45 vs 0.34; P < .0001) or endometrial (0.46 vs 0.40; P = .044) carcinomas and gluteal muscle were higher on 3D images, but those between leiomyoma and myometrium (0.33 vs 0.43; P < .0001) were lower than those on 2D images. Image quality (P = .0004) and carcinoma conspicuity (P < .0005) were superior with the 3D T2-weighted TSE sequence. Although multiplanar reconstruction of 3D T2-weighted TSE images was useful for staging in one case, there were no significant differences between 3D and 2D T2-weighted TSE imaging in accuracy of staging for the two readers for cervical or endometrial carcinoma. The 3D T2-weighted TSE sequence showed certain advantages over the 2D T2-weighted TSE sequence, and it has the potential to improve the performance of MR imaging for the evaluation of uterine carcinoma.

Radiologic and Pathologic Findings in Breast Tumors with High Signal Intensity on T2-weighted MR Images

Various histopathologic components in benign and malignant breast lesions may generate hyperintense signal at T2-weighted magnetic resonance (MR) imaging. A comparison of the specific histologic features found in breast lesions with a high-signal-intensity appearance on unenhanced T2-weighted turbo spin-echo MR images obtained without spectral fat suppression shows that this MR imaging characteristic is often suggestive of the differential diagnosis. Histopathologic features that may produce high signal intensity in breast lesions include extensive necrosis, a cystic or microcystic component, an adipose or sebaceous component, mucinous stroma, loose myxoid stroma, stromal edema, and hemorrhagic changes. A more nuanced understanding of the correlation between the MR imaging appearance and specific pathologic findings may help radiologists achieve earlier and more accurate differentiation among this group of breast lesions.

Rectal Cancer: MR Imaging in Local Staging—Is Gadolinium-based Contrast Material Helpful?

To determine retrospectively whether addition of gadolinium-enhanced T1-weighted magnetic resonance (MR) sequence to T2-weighted turbo spin-echo (SE) MR imaging is valuable for preoperative assessment of T stage and circumferential resection margin in patients with primary rectal cancer. Local institutional review board approved study and waived informed patient consent. Eighty-three patients with operable primary rectal cancer underwent preoperative MR imaging. Retrospectively, two observers independently scored T2-weighted turbo SE MR images and, in a second reading, T2-weighted images combined with gadolinium-enhanced T1-weighted turbo SE MR images for tumor penetration through rectal wall and tumor extension into mesorectal fascia. A confidence level scoring system was used, and receiver operating characteristic (ROC) curves were generated. Histologic findings were standard of reference. Difference in performance of T2-weighted and combined T2-weighted plus gadolinium-enhanced T1-weighted sequences was analyzed by comparing corresponding areas under ROC curves (A(z)) for each observer. Interobserver agreement was calculated by using linear weighted kappa statistics. Addition of contrast-enhanced T1-weighted to T2-weighted MR imaging did not significantly improve diagnostic accuracy for prediction of tumor penetration through rectal wall (A(z) of T2-weighted vs T2-weighted plus T1-weighted images for observer 1, 0.740 vs 0.764; observer 2, 0.856 vs 0.768) and tumor extension into mesorectal fascia (A(z) for observer 1, 0.962 vs 0.902; observer 2, 0.902 vs 0.911). Diagnostic performance (A(z)) of MR and interobserver agreement were high for prediction of tumor extension into mesorectal fascia (kappa = 0.61, 0.74) but only moderate for penetration through rectal wall (kappa = 0.47, 0.45). Gadolinium-enhanced MR sequences did not improve diagnostic accuracy for assessment of tumor penetration through rectal wall and tumor extension into mesorectal fascia.

Characterization of focal liver lesions with superparamagnetic iron oxide-enhanced MR imaging: value of distributional phase T1-weighted imaging.

ObjectiveTo determine the potential value of distributional-phase T1-weighted ferumoxides-enhanced magnetic resonance (MR) imaging for tissue characterization of focal liver lesions.Materials and MethodsFerumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients referred for evaluation of known or suspected hepatic malignancies. Seventy-three focal liver lesions (30 hepatocellular carcinomas [HCC], 12 metastases, 15 cysts, 13 hemangiomas, and three cholangiocarcinomas) were evaluated. MR imaging included T1-weighted double-echo gradient-echo (TR/TE: 150/4.2 and 2.1 msec), T2*-weighted gradient-echo (TR/TE: 180/12 msec), and T2-weighted turbo spin-echo MR imaging at 1.5 T before and after intravenous administration of ferumoxides (15 mmol/kg body weight). Postcontrast T1-weighted imaging was performed within eight minutes of infusion of the contrast medium (distributional phase). Both qualitative and quantitative analysis was performed.ResultsDuring the distributional phase after infusion of ferumoxides, unique enhancement patterns of focal liver lesions were observed for hemangiomas, metastases, and hepatocellular carcinomas. On T1-weighted GRE images obtained during the distributional phase, hemangiomas showed a typical positive enhancement pattern of increased signal; metastases showed ring enhancement; and hepatocellar carcinomas showed slight enhancement. Quantitatively, the signal-to-noise ratio of hemangiomas was much higher than that of other tumors (p < .05) and was similar to that of intrahepatic vessels. This finding permitted more effective differentiation between hemangiomas and other malignant tumors.ConclusionT1-weighted double-echo FLASH images obtained soon after the infusion of ferumoxides, show characteristic enhancement patterns and improved the differentiation of focal liver lesions.

Hepatocellular carcinoma: detection with gadolinium- and ferumoxides-enhanced MR imaging of the liver.

To test the hypothesis that the accuracy of gadolinium- and ferumoxides-enhanced magnetic resonance (MR) imaging is different in small (< or =1.5-cm) and large (>1.5-cm) hepatocellular carcinomas (HCCs). Forty-three consecutive patients with chronic liver disease were enrolled in this study. The imaging protocol included unenhanced breath-hold T1-weighted fast field-echo sequences, unenhanced respiratory-triggered T2-weighted turbo spin-echo (SE) sequences, dynamic gadolinium-enhanced T1-weighted three-dimensional turbo field-echo sequences, and ferumoxides-enhanced T2-weighted turbo SE sequences. Images of each sequence and two sets of sequences (ferumoxides set and gadolinium set) were reviewed by four observers. The ferumoxides set included unenhanced T1- and T2-weighted images and ferumoxides-enhanced T2-weighted turbo SE MR images. The gadolinium set included unenhanced T1- and T2-weighted images and dynamic gadolinium-enhanced three-dimensional turbo field-echo MR images. In receiver operating characteristic (ROC) curve analysis, the sensitivity and accuracy of the sequences were compared in regard to the detection of all, small, and large HCCs. Imaging performance was different with gadolinium- and ferumoxides-enhanced images in the detection of small and large HCCs. For detection of small HCCs, the sensitivity and accuracy with unenhanced and gadolinium-enhanced imaging (gadolinium set) were significantly (P =.017) superior to those with unenhanced and ferumoxides-enhanced imaging (ferumoxides set). The area under the composite ROC curves, or A(z), for the gadolinium set and the ferumoxides set was 0.97 and 0.81, respectively. For large HCC, the ferumoxides set was superior compared with the gadolinium set, but this difference was not statistically significant. Analysis of all HCCs demonstrated no significant differences for gadolinium- and ferumoxides-enhanced imaging. For the detection of early HCC, gadolinium-enhanced MR imaging is preferred to ferumoxides-enhanced MR imaging because the former demonstrated significantly greater accuracy in the detection of small HCCs.

Hepatocellular carcinoma and dysplastic nodules in patients with cirrhosis: prospective diagnosis with MR imaging and explantation correlation.

To determine the sensitivity and specificity of magnetic resonance (MR) imaging for detection of hepatocellular carcinoma (HCC) and dysplastic nodules (DNs) by using explantation correlation in patients with cirrhosis and no known HCC. Seventy-one patients without a known history of HCC who underwent MR imaging and subsequent transplantation within 90 days were examined. Breath-hold turbo short inversion time inversion-recovery and/or T2-weighted turbo spin-echo MR images were obtained. Dynamic two- or three-dimensional gadolinium-enhanced gradient-echo MR images were obtained in the hepatic arterial, portal venous, and equilibrium phases. Prospective MR image interpretations were compared directly with explanted liver pathologic results. Eleven (15%) of 71 patients had hepatic malignancies; MR imaging enabled diagnosis of tumor in six (54%) of 11 patients. On a lesion-by-lesion basis, MR imaging depicted 11 of 20 hepatic neoplasms, for an overall sensitivity of 55%. MR imaging depicted four (80%) of five lesions larger than 2 cm, six (50%) of 12 lesions 1-2 cm, and one (33%) of three lesions smaller than 1 cm. MR imaging depicted only nine (15%) of 59 DNS: The specificities of MR imaging for detection of HCC and DNs on a per patient basis were 60 (86%) of 70 patients and 53 (85%) of 62 patients, respectively. MR imaging is insensitive for the diagnosis of small (<2-cm) HCCs and DNS:

Endoluminal MR imaging of the rectum and anus: technique, applications, and pitfalls.

Anorectal diseases (e.g., fecal incontinence, perianal and anovaginal fistulas, anorectal tumors) require imaging for proper case management. Endoluminal magnetic resonance (MR) imaging has become an important part of diagnostic work-up in such cases. Optimal endoluminal MR imaging requires careful attention to patient preparation, imaging protocols, and potential pitfalls in interpretation. Comfortable positioning and the use of an antiperistaltic drug are vital for adequate patient preparation. Selected sequences and imaging planes are used in imaging protocols tailored for specific diseases. In fecal incontinence, three-dimensional sequences allow detailed demonstration of the anal anatomy and related defects. In perianal and anovaginal fistulas, longitudinal imaging planes help determine the superior extent of the abnormality. In anorectal tumors, T1-weighted turbo spin-echo MR imaging can help detect extension into the perirectal fat and T2-weighted turbo spin-echo MR imaging is used to optimize contrast between tumor and the rectal wall. Off-axis and radial imaging planes are used in all anorectal diseases to minimize partial volume effects. Potential pitfalls include various parts of the normal anal anatomy mimicking sphincter defects, veins and hemorrhoids mimicking fistulas and abscesses, and overhanging tumor mimicking more extensive tumor. Adequate patient preparation combined with proper technique and a knowledge of potential pitfalls will allow optimal endoluminal MR imaging of the rectum and anus.

Cardiac abnormalities: assessment with T2-weighted turbo spin-echo MR imaging with electrocardiogram gating at 0.5 T.

To evaluate the cardiovascular system with magnetic resonance (MR) imaging performed with the turbo spin-echo (TSE) method and electrocardiogram (ECG) gating. ECG-gated T2-weighted TSE images were obtained in 52 patients with 68 pathologic conditions (intracardiac [n = 18], myocardial [n = 23], pericardial [n = 6], paracardial [n = 10], or aortic [n = 11] disease) and 10 healthy subjects. In healthy subjects, TSE parameters were tested and optimized, and signal-to-noise ratios (S/Ns) and contrast-to-noise ratios (C/Ns) were determined. Delineation of the endo-, epi-, and pericardial borders and signal intensity characteristics of myocardium, fat, pericardium, blood flow, tumors, and clots were assessed. The TSE method provided good-quality T2-weighted images with sharp edge definition in a short imaging time. Increasing the turbo factor reduced motion artifacts and preserved the S/N and C/N. TSE images also helped in diagnosis of tumors, pleural effusions, inflammatory changes, and intravascular clots. TSE MR imaging is a feasible alternative to time-consuming conventional SE MR imaging, reduces motion artifact, and may help in evaluation of the cardiovascular system.

9 - Therapeutic Materials used in the Treatment of Coagulation Defects

To test whether iron oxide (IO)–containing yttrium aluminosilicate (YAS) microparticles (MPs) can generate localized therapeutic hyperthermia (≥ 43°C) when injected intratumorally in an animal model of liver cancer and whether MP distributions could be visualized with magnetic resonance (MR) imaging.Twenty-one Sprague–Dawley rats implanted with N1-S1 liver tumors were assigned to alternating magnetic field (AMF) exposure following intratumoral injection with IO-YAS MPs (n = 7), sham surgery (n = 7), or baseline iron quantification (n = 7). Three fiberoptic probes allowed spatial and temporal monitoring of temperatures during 24 minutes of AMF exposure. T2-weighted turbo spin-echo MR imaging was performed within 1 hour after the procedure to detect signal voids caused by IO-YAS deposition. Hematoxylin and eosin–stained pathologic slides were also obtained, and the presence of IO-YAS was evaluated with inductively coupled plasma optical emission spectroscopy.Following AMF exposure, intratumoral temperatures after IO-YAS MP injection achieved therapeutic hyperthermia whereas those after sham surgery did not (46.6°C ± 1.3 vs 36.8°C ± 0.4; P < .0001). Within the treated group, the normal hepatic parenchyma (NHP) and rectal temperatures were 37.4°C ± 0.9 and 36.5°C ± 1.0 (P = .0809) at the conclusion of AMF exposure, respectively. A T2-weighted signal void at the tumor site was observed in all seven treated animals, and intratumoral IO-YAS was visualized on subsequent histopathologic examination in each case. The mean ratio of tumor:NHP Fe concentrations attributable to IO-YAS MPs was 108:1.AMF exposure of intratumoral IO-YAS MPs generates localized therapeutic hyperthermia in an animal model of liver cancer. MR detectability and potential for combination brachytherapy warrants further investigation for thermoradiotherapy in liver cancer.