Feasibility of accelerated whole-body diffusion-weighted imaging using a deep learning-based noise-reduction technique in patients with prostate cancer.

PURPOSE: To assess the possibility of reducing the image acquisition time for diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) by denoising with deep learning-based reconstruction (dDLR). METHODS: Seventeen patients with prostate cancer who underwent DWIBS by 1.5 T magnetic resonance imaging with a number of excitations of 2 (NEX2) and 8 (NEX8) were prospectively enrolled. The NEX2 image data were processed by dDLR (dDLR-NEX2), and the NEX2, dDLR-NEX2, and NEX8 image data were analyzed. In qualitative analysis, two radiologists rated the perceived coarseness, conspicuity of metastatic lesions (lymph nodes and bone), and overall image quality. The contrast-to-noise ratios (CNRs), contrast ratios, and mean apparent diffusion coefficients (ADCs) of metastatic lesions were calculated in a quantitative analysis. RESULTS: The image acquisition time of NEX2 was 2.8 times shorter than that of NEX8 (3 min 30 s vs 9 min 48 s). The perceived coarseness and overall image quality scores reported by both readers were significantly higher for dDLR-NEX2 than for NEX2 (P = 0.005-0.040). There was no significant difference between dDLR-NEX2 and NEX8 in the qualitative analysis. The CNR of bone metastasis was significantly greater for dDLR-NEX2 than for NEX2 and NEX8 (P = 0.012 for both comparisons). The contrast ratios and mean ADCs were not significantly different among the three image types. CONCLUSIONS: dDLR improved the image quality of DWIBS with NEX2. In the context of lymph node and bone metastasis evaluation with DWIBS in patients with prostate cancer, dDLR-NEX2 has potential to be an alternative to NEX8 and reduce the image acquisition time.

Fat-forming solitary fibrous tumor of the sacrum: A case report and literature review.

Fat-forming variant of solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm. Here we report the case of a 33-year-old woman who developed pain and muscle weakness from the posterior aspect of the right hip to lower extremity. Imaging examinations revealed a mass with fatty components and hypervascular solid components filling the sacral spinal canal and sacral foramen. The sacral mass was resected and histological examination of the specimens revealed patternless proliferation of short spindle-shaped cells with staghorn blood vessels. A number of mature adipocyte-like cells were also observed. The tumor cells were positive for STAT6 and the nuclei of the adipocytes were also positive, which was diagnostic for fat-forming SFT.

Recognizing Radiation-induced Changes in the Central Nervous System: Where to Look and What to Look For.

Radiation therapy (RT) continues to play a central role as an effective therapeutic modality for a variety of tumors and vascular malformations in the central nervous system. Although the planning and delivery techniques of RT have evolved substantially during the past few decades, the structures surrounding the target lesion are inevitably exposed to radiation. A wide variety of radiation-induced changes may be observed at posttreatment imaging, which may be confusing when interpreting images. Histopathologically, radiation can have deleterious effects on the vascular endothelial cells as well as on neuroglial cells and their precursors. In addition, radiation induces oxidative stress and inflammation, leading to a cycle of further cellular toxic effects and tissue damage. On the basis of the time of expression, radiation-induced injury can be divided into three phases: acute, early delayed, and late delayed. Acute and early delayed injuries are usually transient and reversible, whereas late delayed injuries are generally irreversible. The authors provide a comprehensive review of the timeline and expected imaging appearances after RT, including the characteristic imaging features after RT with concomitant chemotherapy. Specific topics discussed are imaging features that help distinguish expected posttreatment changes from recurrent disease, followed by a discussion on the role of advanced imaging techniques. Knowledge of the RT plan, the amount of normal structures included, the location of the target lesion, and the amount of time elapsed since RT is highly important at follow-up imaging, and the reporting radiologist should be able to recognize the characteristic imaging features after RT and differentiate these findings from tumor recurrence. ©RSNA, 2020.

Treatment margins in radiotherapy for liver tumors visualized as T2*-hypointense areas on SPIO-enhanced MRI at 9.4 T.

OBJECTIVE: To investigate whether a SPIO-labeling technique could enable MR visualization of the treatment margin after X-irradiation at a single dose of 30 Gy. MATERIALS AND METHODS: Fifteen rats bearing N1-S1 hepatoma in either the left (group 1) or right (group 2) liver lobe were examined. Four hours after systemic SPIO administration, the left lobe was selectively irradiated at 30 Gy. Liver T2* maps were acquired 7 days later using a 9.4 T scanner. The livers were excised and examined histologically. RESULTS: The irradiated area showed T2*-weighted hypointensity with significantly shorter T2* values than those in the non-irradiated area (p < 0.001). Tumors in group 1 completely disappeared, whereas tumors in group 2 had grown outside the T2*-weighted hypointensity by up to ~ 2.3 times that at baseline. Group 1 showed significantly higher probability of tumor regression than group 2 (p = 0.048). Histologically, iron deposition was heavier in irradiated areas than in non-irradiated areas. DISCUSSION: Even at a single dose of 30 Gy, which is a slightly higher dose than can be used clinically in stereotactic body radiotherapy, MR visualization of the treatment margin was achieved, because tumors showed significant growth outside the T2*-hypointense areas. In contrast, tumors disappeared inside the T2*-hypointense areas.

Persistent T2*-hypointensity of the liver parenchyma after irradiation to the SPIO-accumulated liver: An imaging marker for responses to radiotherapy in hepatic malignancies.

PURPOSE: To determine whether T2*-weighted MRI has the ability to visualize the irradiated liver parenchyma and liver tumor after irradiation to the previously superparamagnetic iron oxide (SPIO)-accumulated liver. MATERIALS AND METHODS: We examined 24 liver tumor-bearing rats. Nine rats (Group 1) received 20 µmol Fe/kg SPIO and subsequent 70-Gy irradiation to the tumor-bearing liver lobe. Four rats (Group 2) received SPIO and sham irradiation. Six rats (Group 3) received saline and irradiation. Finally, five rats (Group 4) received saline and sham irradiation. We acquired sequential 3 Tesla T2*-weighted images of the liver on day 7, and assessed MR image findings including signal intensity of the tumors and tumor-bearing liver lobes. RESULTS: In six rats in Group 1, tumors shrunk by 39-100% (303-0 mm3 ), and severely, well-defined hypointense irradiated areas were observed. In the other two rats, tumors enlarged by 25 and 172% (595 and 1148 mm3 ), and hypointense rings surrounded the tumors. The normalized relative signal intensity of the irradiated areas was significantly lower than that of the tumor (0.53 ± 0.06 versus 0.94 ± 0.06; P < 0.05). The severely, well-defined hypointense areas were not observed in the other groups. Histologically, necrotic regions dominated and minimal nonnecrotic tumor cells remained in irradiated areas. The number of CD68-positive cells was higher in irradiated areas than in nonirradiated areas. CONCLUSION: T2*-weighted MR imaging visualized the irradiated liver parenchyma as markedly, well-defined hypointense areas and liver cancer lesions as hyperintense areas only when SPIO was administered before irradiation. The visualization of the hypointense area was associated with tumor regression after irradiation. LEVEL OF EVIDENCE: 2 J. Magn. Reson. Imaging 2017;45:303-312.

Magnetic resonance-based visualization of thermal ablative margins around hepatic tumors by means of systemic ferucarbotran administration before radiofrequency ablation: animal study to reveal the connection between excess iron deposition and T2*-weighted hypointensity in ablative margins.

OBJECTIVE: The objective of this study was to demonstrate experimentally that radiofrequency ablation (RFA) of ferucarbotran-accumulated healthy liver tissues causes excess iron deposition in the ablated liver tissues on postablation days and produces sustained T2*-weighted low signals indicative of ablative margins surrounding hepatic tumors. MATERIALS AND METHODS: We conducted 3 experiments using 30 rats. In experiment 1, we administered either ferucarbotran (n = 6) or saline (n = 4), acquired T2*-weighted images (T2*-WIs) of the liver by using a 3-T magnetic resonance scanner, and subsequently performed RFA of healthy liver lobes. We acquired follow-up T2*-WIs up to day 7 and histologically analyzed the liver specimens. In another 4 rats, we performed sham operation, instead of RFA, in ferucarbotran-accumulated liver lobes, followed by the same image acquisition and histological analysis. In experiment 2, we administered 59Fe-labeled ferucarbotran, subsequently performed either RFA (n = 4) or sham operation (n = 4) in the liver, and acquired autoradiograms of the liver specimens on day 7. In experiment 3, we conducted RFA treatment for 8 rats bearing orthotopic hepatic tumors after ferucarbotran administration and monitored tumor growth by using serial T2*-WIs. RESULTS: On days 4 and 7 of the experiment 1, T2*-WIs of 6 rats with systemic ferucarbotran administration and subsequent hepatic RFA showed low-signal regions indicative of ablated liver tissues, whereas high-signal areas were seen in 4 saline-administered rats. Neither high nor low signal areas were detected in 4 sham-operated rats. Histologically, larger amounts of iron were observed in the RFA-induced necrotic liver tissues in the ferucarbotran-administered rats than in the saline-administered-rats. The 59Fe autoradiography of the rats in experiment 2 revealed accumulation of ferucarbotran-derived iron in necrotic liver tissues. Among 6 hepatic tumors grown in 6 rats of the experiment 3, a total of 4 tumors were stable in size, but the other 2 increased markedly on day 7. Retrospectively, T2*-WIs showed the former tumor sites surrounded completely by low-signal areas on day 4. CONCLUSIONS: The RFA of ferucarbotran-accumulated healthy liver tissues in the rats caused excess iron deposition in the ablated liver tissues and produced sustained T2*-weighted hypointense regions. Similar hypointense regions surrounding hepatic tumors were indicative of ablative margins.

Detection of lung tumors in mice using a 1-tesla compact magnetic resonance imaging system.

Due to their small size, lung tumors in rodents are typically investigated using high-field magnetic resonance (MR) systems (4.7 T or higher) to achieve higher signal-to-noise ratios, although low-field MR systems are less sensitive to susceptibility artifacts caused by air in the lung. We investigated the feasibility of detecting lung tumors in living, freely breathing mice with a 1-T compact permanent magnet MR system. In total, 4 mice were used, and MR images of mouse lungs were acquired using a T1-weighted three-dimensional fast low-angle shot sequence without cardiac or respiratory gating. The delineation and size of lung tumors were assessed and compared with histopathological findings. Submillimeter lesions were demonstrated as hyperintense, relative to the surrounding lung parenchyma, and were delineated clearly. Among the 13 lesions validated in histopathological sections, 11 were detected in MR images; the MR detection rate was thus 84.6%. A strong correlation was obtained in size measurements between MR images and histological sections. Thus, a dedicated low-field MR system can be used to detect lung tumors in living mice noninvasively without gating.

Erdheim-Chester disease with an 18F-fluorodeoxyglucose-avid breast mass and BRAF V600E mutation.

Erdheim-Chester disease (ECD) is a non-Langerhans cell histiocytosis. Herein we report a case of a 49-year-old woman who developed bilateral knee pain. Imaging procedures revealed multiple long bone lesions and a well-defined 18F-fluorodeoxyglucose-avid mass in the left breast. The breast mass was resected, and an open biopsy was performed on the right femoral lesion. Both specimens revealed involvement by histiocytic infiltrates with features suggestive of ECD. The BRAF V600E mutation was detected by DNA sequencing and immunohistochemistry.

Artifact-reduced simultaneous MRI of multiple rats with liver cancer using PROPELLER.

PURPOSE: To explore simultaneous magnetic resonance imaging (MRI) for multiple hepatoma-bearing rats in a single session suppressing motion- and flow-related artifacts to conduct preclinical cancer research efficiently. MATERIALS AND METHODS: Our institutional Animal Experimental Committee approved this study. We acquired PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) T2 - and diffusion-weighted images of the liver in one healthy and 11 N1-S1 hepatoma-bearing rats in three sessions using a 3-T clinical scanner and dedicated multiarray coil. We compared tumor volumes on MR images and those on specimens, evaluated apparent diffusion coefficients (ADC) of the tumor, and compared them to previously reported values. RESULTS: Each MRI session took 39-50 minutes from anesthesia induction to the end of scans for four rats (10-13 minutes per rat). PROPELLER provided artifact-reduced T2 - and diffusion-weighted images of the rat livers. Tumor volumes on MR images ranged from 0.04-1.81 cm(3) and were highly correlated with those on specimens. The ADC was 1.57 ± 0.37 × 10(-3) mm(2) /s (average ± SD), comparable to previously reported values. CONCLUSION: PROPELLER allowed simultaneous acquisition of artifact-reduced T2 - and diffusion-weighted images of multiple hepatoma-bearing rats. This technique can promote high-throughput preclinical MR research for liver cancer.

Multiple-animal MR imaging using a 3T clinical scanner and multi-channel coil for volumetric analysis in a mouse tumor model.

PURPOSE: Multiple small-animal magnetic resonance (MR) imaging to measure tumor volume may increase the throughput of preclinical cancer research assessing tumor response to novel therapies. We used a clinical scanner and multi-channel coil to evaluate the usefulness of this imaging to assess experimental tumor volume in mice. METHODS: We performed a phantom study to assess 2-dimensional (2D) geometric distortion using 9-cm spherical and 32-cell (8×4 one-cm(2) grids) phantoms using a 3-tesla clinical MR scanner and dedicated multi-channel coil composed of 16 5-cm circular coils. Employing the multi-channel coil, we simultaneously scanned 6 or 8 mice bearing sarcoma 180 tumors. We estimated tumor volume from the sum of the product of tumor area and slice thickness on 2D spin-echo images (repetition time/echo time, 3500/16 ms; in-plane resolution, 0.195×0.195×1 mm(3)). After MR acquisition, we excised and weighed tumors, calculated reference tumor volumes from actual tumor weight assuming a density of 1.05 g/cm(3), and assessed the correlation between the estimated and reference volumes using Pearson's test. RESULTS: Two-dimensional geometric distortion was acceptable below 5% in the 9-cm spherical phantom and in every cell in the 32-cell phantom. We scanned up to 8 mice simultaneously using the multi-channel coil and found 11 tumors larger than 0.1 g in 12 mice. Tumor volumes were 1.04±0.73 estimated by MR imaging and 1.04±0.80 cm(3) by reference volume (average±standard deviation) and highly correlated (correlation coefficient, 0.995; P<0.01, Pearson's test). CONCLUSION: Use of multiple small-animal MR imaging employing a clinical scanner and multi-channel coil enabled accurate assessment of experimental tumor volume in a large number of mice and may facilitate high throughput monitoring of tumor response to therapy in preclinical research.

Hepatic segments and vasculature: projecting CT anatomy onto angiograms.

Hepatic transarterial interventional therapies such as chemoembolization and radiation embolization are important treatment options for hepatocellular carcinoma. Understanding the anatomy of individual arterial branches and hepatic segments is critical for selecting the correct embolization technique for treatment and to avoid complications. The authors describe the morphologic characteristics of hepatic arterial branches (and their mimickers) and hepatic segments on conventional angiograms. These vessels and segments include the celiac artery, the common and proper hepatic arteries, the left and right hepatic arteries and branches, the caudate lobe, and the portal vein and branches. Mimickers of hepatic arteries include the cystic, accessory left gastric, and right gastric arteries, as well as branches of the left gastric artery that resemble segmental branches of the replaced left hepatic artery. The authors describe how each segmental branch of the hepatic artery and the area it supplies correlates at computed tomography (CT) and angiography. Finally, the authors demonstrate how the vascular anatomy changes with the respiratory cycle by creating a virtual movie from calculations with dynamic CT data, in which the arterial and venous phases are acquired at end expiration and inspiration, respectively. Each segmental branch of the hepatic artery has morphologic characteristics that help distinguish it from mimickers. The location of each hepatic segment can be estimated if the artery supplying the segment can be correctly identified on angiograms. Notably, morphologic differences in the hepatic artery system caused by respiration should be recognized.

Hepatic Segments and Vasculature: Projecting CT Anatomy onto Angiograms.

Hepatic transarterial interventional therapies such as chemoembolization and radiation embolization are important treatment options for hepatocellular carcinoma. Understanding the anatomy of individual arterial branches and hepatic segments is critical for selecting the correct embolization technique for treatment and to avoid complications. The authors describe the morphologic characteristics of hepatic arterial branches (and their mimickers) and hepatic segments on conventional angiograms. These vessels and segments include the celiac artery, the common and proper hepatic arteries, the left and right hepatic arteries and branches, the caudate lobe, and the portal vein and branches. Mimickers of hepatic arteries include the cystic, accessory left gastric, and right gastric arteries, as well as branches of the left gastric artery that resemble segmental branches of the replaced left hepatic artery. The authors describe how each segmental branch of the hepatic artery and the area it supplies correlates at computed tomography (CT) and angiography. Finally, the authors demonstrate how the vascular anatomy changes with the respiratory cycle by creating a virtual movie from calculations with dynamic CT data, in which the arterial and venous phases are acquired at end expiration and inspiration, respectively. Each segmental branch of the hepatic artery has morphologic characteristics that help distinguish it from mimickers. The location of each hepatic segment can be estimated if the artery supplying the segment can be correctly identified on angiograms. Notably, morphologic differences in the hepatic artery system caused by respiration should be recognized.