A Case of Rectal Dissemination of Gastric Cancer Diagnosed by Simultaneous 18 F-FDG PET/MRI.

ABSTRACT: Metastatic rectal cancer is rare and difficult to differentiate from primary rectal cancer. A 79-year-old man with a rectal mass detected by CT during postoperative follow-up of gastric cancer underwent 18 F-FDG PET/MRI. Fused PET/MRI images revealed a lower FDG uptake within the mass, which appeared to surround the outside of the rectum, than in the rectal wall, suggesting rectal dissemination of gastric cancer. PET/MRI was useful for differentiating between mass and rectal wall uptake, because of the high contrast resolution of MRI and precise image fusion made possible by simultaneous image acquisition.

Rapid Whole-Body FDG PET/MRI in Oncology Patients: Utility of Combining Bayesian Penalised Likelihood PET Reconstruction and Abbreviated MRI.

This study evaluated the diagnostic value of a rapid whole-body fluorodeoxyglucose (FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) approach, combining Bayesian penalised likelihood (BPL) PET with an optimised ß value and abbreviated MRI (abb-MRI). The study compares the diagnostic performance of this approach with the standard PET/MRI that utilises ordered subsets expectation maximisation (OSEM) PET and standard MRI (std-MRI). The optimal ß value was determined by evaluating the noise-equivalent count (NEC) phantom, background variability, contrast recovery, recovery coefficient, and visual scores (VS) for OSEM and BPL with ß100-1000 at 2.5-, 1.5-, and 1.0-min scans, respectively. Clinical evaluations were conducted for NECpatient, NECdensity, liver signal-to-noise ratio (SNR), lesion maximum standardised uptake value, lesion signal-to-background ratio, lesion SNR, and VS in 49 patients. The diagnostic performance of BPL/abb-MRI was retrospectively assessed for lesion detection and differentiation in 156 patients using VS. The optimal ß values were ß600 for a 1.5-min scan and ß700 for a 1.0-min scan. BPL/abb-MRI at these ß values was equivalent to OSEM/std-MRI for a 2.5-min scan. By combining BPL with optimal ß and abb-MRI, rapid whole-body PET/MRI could be achieved in ≤1.5 min per bed position, while maintaining comparable diagnostic performance to standard PET/MRI.

Influence of Metal Implants on Quantitative Evaluation of Bone Single-Photon Emission Computed Tomography/Computed Tomography.

When visualizing biological activity at nonunion sites by the radioisotopes, gamma rays are more attenuated if metal implants are placed in the bone. However, the effects of various implant types and their placement on gamma ray attenuation in quantitative evaluation remain unknown. To elucidate these effects, we created a phantom that simulated the nonunion of the femur in this study. The count of gamma rays was measured by single-photon emission computed tomography/computed tomography (SPECT/CT) while considering CT-based attenuation correction (CTAC), metal implant placement, type (intramedullary nail or plate), and position. The count differed significantly with and without CTAC and with and without implants (both types) under CTAC. Significantly different counts were observed between the intramedullary nail and plate placed contralaterally to the lesion (i.e., non-lesion side). No significant difference was observed between the intramedullary nail and plate on the lesion side or between plates on the non-lesion and lesion sides. The measured standardized uptake value (SUV) was closer to the true SUV with CTAC than without. Moreover, the count was higher with implants than without. However, even with implants, it was lower than the actual count, indicating the absence of overcorrection. Implant type and position do not seem to influence the count.

Unsupervised-learning-based method for chest MRI-CT transformation using structure constrained unsupervised generative attention networks.

The integrated positron emission tomography/magnetic resonance imaging (PET/MRI) scanner simultaneously acquires metabolic information via PET and morphological information using MRI. However, attenuation correction, which is necessary for quantitative PET evaluation, is difficult as it requires the generation of attenuation-correction maps from MRI, which has no direct relationship with the gamma-ray attenuation information. MRI-based bone tissue segmentation is potentially available for attenuation correction in relatively rigid and fixed organs such as the head and pelvis regions. However, this is challenging for the chest region because of respiratory and cardiac motions in the chest, its anatomically complicated structure, and the thin bone cortex. We propose a new method using unsupervised generative attentional networks with adaptive layer-instance normalisation for image-to-image translation (U-GAT-IT), which specialised in unpaired image transformation based on attention maps for image transformation. We added the modality-independent neighbourhood descriptor (MIND) to the loss of U-GAT-IT to guarantee anatomical consistency in the image transformation between different domains. Our proposed method obtained a synthesised computed tomography of the chest. Experimental results showed that our method outperforms current approaches. The study findings suggest the possibility of synthesising clinically acceptable computed tomography images from chest MRI with minimal changes in anatomical structures without human annotation.

FDG PET/MRI in Synchronous Uterine Adenocarcinoma and Leiomyosarcoma.

ABSTRACT: A 52-year-old woman with a rapidly growing uterine tumor suspected of uterine sarcoma underwent 18F-FDG PET/MRI, revealing a myometrial mass and an endometrial lesion, suggesting dual primary neoplasms. Based on the PET/MRI findings, we changed the intraoperative procedure to determine the necessity of pelvic lymphadenectomy. PET/MRI was useful in diagnosing and differentiating between 2 malignant neoplasms in the uterus compared with PET/CT, due to MRI's high contrast resolution and precise fusion due to the simultaneous acquisition.

Physiological skin FDG uptake: A quantitative and regional distribution assessment using PET/MRI.

PURPOSE: To retrospectively assess the repeatability of physiological F-18 labeled fluorodeoxyglucose (FDG) uptake in the skin on positron emission tomography/magnetic resonance imaging (PET/MRI) and explore its regional distribution and relationship with sex and age. METHODS: Out of 562 examinations with normal FDG distribution on whole-body PET/MRI, 74 repeated examinations were evaluated to assess the repeatability and regional distribution of physiological skin uptake. Furthermore, 224 examinations were evaluated to compare differences in the uptake due to sex and age. Skin segmentation on PET was performed as body-surface contouring on an MR-based attenuation correction map using an off-line reconstruction software. Bland-Altman plots were created for the repeatability assessment. Kruskal-Wallis test was performed to compare the maximum standardized uptake value (SUVmax) with regional distribution, age, and sex. RESULTS: The limits of agreement for the difference in SUVmean and SUVmax of the skin were less than 30%. The highest SUVmax was observed in the face (3.09±1.04), followed by the scalp (2.07±0.53). The SUVmax in the face of boys aged 0-9 years and 10-20 years (1.33±0.64 and 2.05±1.00, respectively) and girls aged 0-9 years (0.98±0.38) was significantly lower than that of men aged ≥20 years and girls aged ≥10 years (p<0.001). In women, the SUVmax of the face (2.31±0.71) of ≥70-year-olds was significantly lower than that of 30-39-year-olds (3.83±0.82) (p<0.05). CONCLUSION: PET/MRI enabled the quantitative analysis of skin FDG uptake with repeatability. The degree of physiological FDG uptake in the skin was the highest in the face and varied between sexes. Although attention to differences in body habitus between age groups is needed, skin FDG uptake also depended on age.

Quantitative bone single-photon emission computed tomography imaging for uninfected nonunion: comparison of hypertrophic nonunion and non-hypertrophic nonunion.

BACKGROUND: Recently, a standardized uptake value (SUV) has been used to evaluate bone single-photon emission computed tomography (SPECT). The aim of this study was to investigate quantitative SPECT imaging of uninfected nonunion to compare hypertrophic nonunion and non-hypertrophic nonunion using volume-based parameters. METHODS: We evaluated 23 patients with uninfected nonunion who underwent SPECT acquisition 3 h after an injection of 99mTc-hydroxymethylene diphosphonate or 99mTc-methylene diphosphonate from April 2014 to November 2019. We reconstructed the acquired data and performed voxel-based quantitative analysis using the GI-BONE software. Quantitative parameters, maximum SUV (SUVmax), peak SUV (SUVpeak), and mean SUV (SUVmean) in the high and low uptake areas of nonunion were compared between hypertrophic nonunion and non-hypertrophic nonunion. The contralateral limb was used as a control, and the ratios of the quantitative parameters were calculated. RESULTS: The values for the quantitative parameters (high uptake area/low uptake area, respectively), SUVmax control ratio (12.13 ± 4.95/6.44 ± 4.71), SUVpeak control ratio (11.65 ± 4.58/6.45 ± 4.64), and SUVmean control ratio (11.94 ± 5.03/6.28 ± 4.95) for hypertrophic nonunion were higher than those for non-hypertrophic nonunion (7.82 ± 4.76/3.41 ± 2.09 (p = 0.065/0.12), 7.56 ± 4.51/3.61 ± 2.23 (p = 0.065/0.22), and 7.59 ± 5.18/3.05 ± 1.91 (p = 0.076/0.23)). CONCLUSIONS: SUVmax, SUVpeak, and SUVmean control ratios obtained from bone SPECT images can quantitatively evaluate the biological activity of nonunions and may be an effective evaluation method for treatment decisions, especially the necessity of autologous bone grafting.

Dose-dependent accumulation of glucose in the intestinal wall and lumen induced by metformin as revealed by 18 F-labelled fluorodeoxyglucose positron emission tomography-MRI.

AIM: To investigate the relationships between various clinical variables and the metformin-induced accumulation of fluorodeoxyglucose (FDG) in the intestine, with distinction between the intestinal wall and lumen, in individuals with type 2 diabetes who were receiving metformin treatment and underwent 18 F-labelled FDG ([18 F]FDG) positron emission tomography (PET)-MRI. MATERIALS AND METHODS: We evaluated intestinal accumulation of [18 F]FDG with both subjective (a five-point visual scale determined by two experienced radiologists) and objective analyses (measurement of the maximum standardized uptake value [SUVmax ]) in 26 individuals with type 2 diabetes who were receiving metformin and underwent [18 F]FDG PET-MRI. [18 F]FDG accumulation within the intestinal wall was discriminated from that in the lumen on the basis of SUVmax . RESULTS: SUVmax for the large intestine was correlated with blood glucose level (BG) and metformin dose, but not with age, body mass index, HbA1c level or estimated glomerular filtration rate (eGFR). SUVmax for the small intestine was not correlated with any of these variables. Visual scale analysis yielded essentially similar results. Metformin dose and eGFR were correlated with SUVmax for the wall and lumen of the large intestine, whereas BG was correlated with that for the wall. Multivariable analysis identified metformin dose as an explanatory factor for SUVmax in the wall and lumen of the large intestine after adjustment for potential confounders including BG and eGFR. CONCLUSIONS: Metformin dose is an independent determinant of [18 F]FDG accumulation in the wall and lumen of the large intestine in individuals treated with this drug.

Enhanced Release of Glucose Into the Intraluminal Space of the Intestine Associated With Metformin Treatment as Revealed by [18F]Fluorodeoxyglucose PET-MRI.

OBJECTIVE: Positron emission tomography (PET)-computed tomography has revealed that metformin promotes the intestinal accumulation of [18F]fluorodeoxyglucose (FDG), a nonmetabolizable glucose derivative. It has remained unknown, however, whether this accumulation occurs in the wall or intraluminal space of the intestine. We here addressed this question with the use of [18F]FDG PET-MRI, a recently developed imaging method with increased accuracy of registration and high soft-tissue contrast. RESEARCH DESIGN AND METHODS: Among 244 individuals with type 2 diabetes who underwent PET-MRI, we extracted 24 pairs of subjects matched for age, BMI, and HbA1c level who were receiving treatment with metformin (metformin group) or were not (control group). We evaluated accumulation of [18F]FDG in different portions of the intestine with both a visual scale and measurement of maximum standardized uptake value (SUVmax), and such accumulation within the intestinal wall or lumen was discriminated on the basis of SUVmax. RESULTS: SUVmax of the jejunum, ileum, and right or left hemicolon was greater in the metformin group than in the control group. [18F]FDG accumulation in the ileum and right or left hemicolon, as assessed with the visual scale, was also greater in the metformin group. SUVmax for the intraluminal space of the ileum and right or left hemicolon, but not that for the intestinal wall, was greater in the metformin group than in the control group. CONCLUSIONS: Metformin treatment was associated with increased accumulation of [18F]FDG in the intraluminal space of the intestine, suggesting that this drug promotes the transport of glucose from the circulation into stool.

Magnetic resonance imaging of intraocular optic nerve disorders: review article.

The optic nerve is morphologically classified as a peripheral nerve, but histologically it shares characteristics with the central nerves. Diseases that affect vision and the optic nerve are many and varied: optic neuritis, demyelination (multiple sclerosis, acute disseminated encephalomyelitis, neuromyelitis optica spectrum disorder, and myelin oligodendrocyte glycoprotein antibody-related disorders), drugs, collagen disease, vasculitis, infection, trauma, vascular abnormalities, tumours, and non-tumoural masses. In this review, we summarise the magnetic resonance imaging findings for various pathological conditions that cause deterioration in visual acuity.

Diagnostic performance of zero-TE lung MR imaging in FDG PET/MRI for pulmonary malignancies.

OBJECTIVES: This study aimed to evaluate the diagnostic performance of the lung zero-echo time (ZTE) sequence in FDG PET/MRI for detection and differentiation of lung lesions in oncologic patients in comparison with conventional two-point Dixon-based MR imaging. METHODS: In this single-institution retrospective study approved by the institutional review board, 209 patients with malignancies (97 men and 112 women; age range, 17-89 years; mean age, 66.5 ± 12.9 years) underwent 18F-FDG PET/MRI between August 2017 and August 2018, with diagnostic Dixon and ZTE under respiratory gating acquired simultaneously with PET. Image analysis was performed for PET/Dixon and PET/ZTE fused images by two readers to assess the detectability and differentiation of lung lesions. The reference standard was pathological findings and/or the data from a chest CT. The detection and differentiation abilities were evaluated for all lesions and subgroups divided by lesion size and maximum standardized uptake value (SUVmax). RESULTS: Based on the reference standard, 227 lung lesions were identified in 113 patients. The detectability of PET/ZTE was significantly better than that of PET/Dixon for overall lesions, lesions with a SUVmax less than 3.0 and lesions smaller than 4 mm (p < 0.01). The diagnostic performance of PET/ZTE was significantly better than that of PET/Dixon for overall lesions and lesions smaller than 4 mm (p < 0.01). CONCLUSIONS: ZTE can improve diagnostic performance in the detection and differentiation of both FDG-avid and non-FDG-avid lung lesions smaller than 4 mm in size, yielding a promising tool to enhance the utility of FDG PET/MRI in oncology patients with lung lesions. KEY POINTS: • The detection rate of PET/ZTE for lesions with a SUVmax of less than 1.0 was significantly better than that of PET/Dixon. • The performance for differentiation of PET/ZTE for lesions that were even smaller than 4 mm in size were significantly better than that of PET/Dixon. • Inter-rater agreement of PET/ZTE for the differentiation of lesions less than 4 mm in size was substantial and better than that of PET/Dixon.

Imaging findings in radiation therapy complications of the central nervous system.

Radiation therapy is a useful treatment for tumors and vascular malformations of the central nervous system. Radiation therapy is associated with complications, including leukoencephalopathy, radiation necrosis, vasculopathy, and optic neuropathy. Secondary tumors are also often seen long after radiation therapy. Secondary tumors are often benign tumors, such as hemangiomas and meningiomas, but sometimes malignant gliomas and soft tissue sarcomas emerge. We review the imaging findings of complications that may occur after brain radiation therapy.

Semi-quantitative dopamine transporter standardized uptake value in comparison with conventional specific binding ratio in [123I] FP-CIT single-photon emission computed tomography (DaTscan).

PURPOSE: We developed a new analytical method to quantify the dopamine transporter (DAT) radiation dose in the striatum on [123I] FP-CIT single-photon emission computed tomography (SPECT). This method is based on the dopamine transporter standardized uptake value (DaTSUV). The purpose of this study was to compare DaTSUV with the classical specific binding ratio (SBR) in the discrimination of dopaminergic neurodegenerative diseases (dNDD) from non-dNDD. METHOD: Seventy-seven consecutive patients who underwent DaTscan were included. Patients were divided into a dNDD group (n = 44; 24 men, 20 women; median age 73 years) and a non-dNDD group (n = 33; 14 men, 19 women; median age 75 years) based on their clinical diagnoses. The relationship between each method was evaluated by Pearson's correlation coefficient. Differences in SBR and DaTSUV in each group were evaluated by t test. Pairwise comparison of receiver operating characteristic (ROC) curve analysis was performed to compare the discriminating abilities of each method according to the standard error of the area under the curve (AUC). A value of p < 0.05 was considered statistically significant. RESULT: There was a significant strong correlation between DaTSUV and SBR (r = 0.910 [95% CI = 0.862-0.942], p < 0.001). The dNDD group showed significantly lower SBR (3.48 [1.25-7.91] vs 6.58 [3.81-11.1], p < 0.001) and DaTSUV (4.91 [1.59-13.6] vs 8.61 [2.29-15.6], p < 0.001) than the non-dNDD group. The discriminating ability of SBR (AUC = 0.918) was significantly higher than that of DaTSUV (AUC = 0.838, p = 0.0176). CONCLUSION: DaTSUV has a good correlation with SBR, but it could not exceed SBR for discriminating dNDD from non-dNDD.

Diffusion-Weighted Imaging Shows a False-Negative Finding for Bone Marrow Involvement on 18F-FDG PET/MRI in a Patient With Malignant Lymphoma After Blood Transfusion.

Iron overload is a major complication in blood transfusion procedures. This report presents a case of malignant lymphoma, in which the findings of bone marrow involvement were discordant between F-FDG PET imaging studies and MRI with diffusion-weighted imaging studies. In this case, the PET imaging studies were positive for malignant lymphoma, whereas the MRI studies were negative. Iron deposition in the reticuloendothelial system due to posttransfusion iron overload was considered to be the cause of the decrease in signal intensity on diffusion-weighted imaging, resulting in a false-negative finding on MRI.

A case of fatal heart and liver failure accompanied by thyroid storm treated with prompt plasma exchange.

A 36-year-old man with a history of Graves' disease was admitted complaining of dyspnea. He was diagnosed with acute heart failure and severe liver dysfunction accompanied by thyroid storm. Left ventricular ejection fraction was 19%, and liver enzyme levels were markedly elevated followed with coagulation disorders. In addition to the conventional therapy, we performed plasma exchange emergently. Thyroid hormone levels promptly normalized, then his clinical condition improved. Finally, his cardiac and liver function almost normalized from a fatal condition without serious complications. Hyperthyroidism can cause myocardial and liver injury, hence thyroid hormone removal in acute phase is important. Prompt plasma exchange is effective in the acute phase for heart and liver failure accompanied by thyroid storm. .