Rikiya Yamashita

Diffusion-weighted magnetic resonance imaging in autoimmune pancreatitis

PurposeThe aim of this study was to investigate the usefulness of diffusion-weighted magnetic resonance imaging (DWI MRI) for the diagnosis and evaluation of autoimmune pancreatitis (AIP).Materials and methodsA total of 4 consecutive patients with AIP, 5 patients with chronic alcoholic pancreatitis (CP), and 13 patients without pancreatic disease (controls) were studied. DWI was performed in the axial plane with spin-echo echo-planar imaging single-shot sequence. Apparent diffusion coefficients (ADCs) were measured in circular regions of interest in the pancreas. In AIP patients, abdominal MRI was performed before, and 2–4 weeks after steroid treatment. Follow-up study was performed chronologically for up to 11 months in two patients. The correlation between ADCs of the pancreas and the immunoglobulin G4 (IgG4) index (serum IgG4 value/serum IgG4 value before steroid treatment) was evaluated.ResultsIn the AIP patients, DWI of the pancreas showed high signal intensity, and the ADCs of the pancreas (mean ± SD: 0.97 ± 0.18 × 10−3 mm2/s) were significantly lower than those in patients with CP (1.45 ± 0.10 × 10−3 mm2/s) or the controls (1.45 ± 0.16 × 10−3 mm2/s) (Mann-Whitney U-test, P < 0.05). In one AIP patient with focal swelling of the pancreas head that appeared to be a mass, DWI showed high signal intensity throughout the pancreas, indicating diffuse involvement. The ADCs of the pancreas and IgG4 index were significantly inversely correlated (Spearman’s rank correlation coefficient, rs = −0.80, P < 0.05).ConclusionAutoimmune pancreatitis showed high signal intensity on DWI, which improved after steroid treatment. ADCs reflected disease activity. Thus, diffusion-weighted MRI might be useful for diagnosing AIP, determining the affected area, and evaluating the effect of treatment.

F-18 fluorodeoxyglucose uptake in a solid pseudopapillary tumor of the pancreas mimicking malignancy.

Solid pseudopapillary tumors (SPTs), predominantly affecting young women, are rare pancreatic tumors. It is reported that imaging features of SPT are solid and cystic components, and there is intratumoral hemorrhage and calcification. However, findings of positron emission tomography (PET) using F-18 fluorodeoxyglucose (FDG) with pathologic correlation have not been fully evaluated. We present a case of SPT that mimicked malignancy on FDG-PET.

Non-contrast-enhanced MR portography with balanced steady-state free-precession sequence and time-spatial labeling inversion pulses: comparison of imaging with flow-in and flow-out methods.

To compare and evaluate images of non–contrast‐enhanced MR portography acquired with two different methods, the flow‐in and flow‐out methods.

Comparison of monopolar and bipolar diffusion weighted imaging sequences for detection of small hepatic metastases

OBJECTIVE To compare monopolar (MP) and bipolar (BP) diffusion weighted imaging (DWI) in detecting small liver metastases. MATERIALS AND METHODS Eighty-eight patients underwent 3-T MRI. The signal-to-noise ratios (SNR) of the liver parenchyma and lesions, the lesion-to-liver contrast-to-noise ratios (CNR), and the detection sensitivities were compared. The lesion distortion was scored (LDS) from 4 (no distortion) to 1 (excessive distortion), dichotomised as no-distortion and distortion, and the association between detected lesions for each reader in the MP or BP DWI group and the dichotomised lesion distortion degree was assessed. RESULT Forty-six hepatic metastases were confirmed. The CNR with BP images showed significantly higher values than with MP (P=0.017). The detection sensitivities of the three readers were higher in the BP sequence than in MP, and one reader detected significantly more hepatic lesions with BP images (P=0.04). LDS was significantly improved with BP sequence (P=0.002). In the no-distortion group, excluding the MP DWI assessments of one reader, detection sensitivities were significantly higher than in the distortion group (P<0.001 and P=0.002, respectively). CONCLUSION Reduced lesion distortion improves the detection of small liver metastases, and BP is more sensitive in detecting small liver metastases than MP DWI.

Convolutional neural networks: an overview and application in radiology.

Convolutional neural network (CNN), a class of artificial neural networks that has become dominant in various computer vision tasks, is attracting interest across a variety of domains, including radiology. CNN is designed to automatically and adaptively learn spatial hierarchies of features through backpropagation by using multiple building blocks, such as convolution layers, pooling layers, and fully connected layers. This review article offers a perspective on the basic concepts of CNN and its application to various radiological tasks, and discusses its challenges and future directions in the field of radiology. Two challenges in applying CNN to radiological tasks, small dataset and overfitting, will also be covered in this article, as well as techniques to minimize them. Being familiar with the concepts and advantages, as well as limitations, of CNN is essential to leverage its potential in diagnostic radiology, with the goal of augmenting the performance of radiologists and improving patient care.Key Points• Convolutional neural network is a class of deep learning methods which has become dominant in various computer vision tasks and is attracting interest across a variety of domains, including radiology.• Convolutional neural network is composed of multiple building blocks, such as convolution layers, pooling layers, and fully connected layers, and is designed to automatically and adaptively learn spatial hierarchies of features through a backpropagation algorithm.• Familiarity with the concepts and advantages, as well as limitations, of convolutional neural network is essential to leverage its potential to improve radiologist performance and, eventually, patient care.

Selective visualization of pelvic splanchnic nerve and pelvic plexus using readout-segmented echo-planar diffusion-weighted magnetic resonance neurography: A preliminary study in healthy male volunteers.

PURPOSE To evaluate the potential of readout-segmented echo-planar diffusion-weighted magnetic resonance neurography (RS-EPI DW-MRN) for the selective visualization of pelvic splanchnic nerve and pelvic plexus in healthy male volunteers. MATERIALS AND METHODS Institutional review board approval and written informed consent were obtained. RS-EPI DW-MRN images were acquired from thirteen healthy male volunteers aged 25-48 years between September 2013 and December 2013. For RS-EPI DW-MRN, the following parameters were used: spatial resolution, 1.1×1.1×2.5mm; b-value, 250s/mm2; number of readout-segments, seven; and acquisition time, 7min 45s. For qualitative assessment, two abdominal radiologists independently evaluated the visibility of the pelvic splanchnic nerves and pelvic plexuses bilaterally in each subject on oblique coronal thin-slab 10-mm-thick maximum intensity projection images and scored it with a 4-point grading scale (excellent, good, fair, poor). Both readers scored twice at 6-month intervals. Inter-observer and intra-observer variability were evaluated using Cohens quadratically weighted κ statistics. Image artifact level was scored on a 4-point grading scale by other two abdominal radiologists in order to evaluate the correlation between the nerve visibility and the severity of imaging artifacts using the Spearmans correlation coefficient. RESULTS Qualitative grading showed the following success rate (number of nerves qualitatively scored as excellent or good divided by total number of nerves): reader 1 (first set), 73% (19/26); reader 2 (first set), 77% (20/26); reader 1 (second set), 81% (21/26); and reader 2 (second set), 77% (20/26). Inter-observer agreement between readers 1 and 2 was excellent: κ=0.947 (first set) and 0.845 (second set). Intra-observer agreement was also excellent: κ=0.810 (reader 1) and 0.946 (reader 2). The visibility of pelvic splanchnic nerve and pelvic plexus showed a moderate correlation with the image artifact level (ρ=0.54, p=0.004). CONCLUSION This study demonstrated that RS-EPI DW-MRN is a promising approach for selectively visualizing the pelvic splanchnic nerve and pelvic plexus.

Imaging of metastases from breast cancer to uncommon sites: a pictorial review

There are three types of breast cancer recurrence which can occur after initial treatment: local, regional, and distant. Distant metastases are more frequent than local and regional recurrences. It usually occurs several years after the primary breast cancer, although it is sometimes diagnosed at the same time as the primary breast cancer. Although the common distant metastases are bone, lung and liver, breast cancer has the potential to metastasize to almost any region of the body. Early detection and treatment of distant metastases improves the prognosis, therefore radiologists and clinicians should recognize the possibility of metastasis from breast cancer and grasp the imaging characteristics. In this report, we demonstrate the imaging characteristics of metastases from breast cancer to uncommon sites.

Additional benefit of computed diffusion-weighted imaging for detection of hepatic metastases at 1.5 T

The aim is to investigate the added value of computed diffusion-weighted magnetic resonance imaging (DWI) at 1.5T in detecting hepatic metastases. Fifty-six patients with a total of 100 hepatic metastases were included. Computed DWI was synthesized from lower b values. Diagnostic performance was evaluated by receiver operating characteristic (ROC) curve analysis. The sensitivity was calculated and analyzed. The area under the ROC curve of the computed DWI was larger than that of acquired DWI. Both readers detected significantly more hepatic metastases with combined acquired DWI/computed DWI. Combined use of computed DWI with acquired DWI helped to provide higher sensitivity at 1.5T.

Non-contrast-enhanced MR portography and hepatic venography with time-spatial labeling inversion pulses: Comparison of imaging with the short tau inversion recovery method and the chemical shift selective method

PURPOSE To compare and evaluate images of non-contrast enhanced magnetic resonance (MR) portography and hepatic venography acquired with two different fat suppression methods, the chemical shift selective (CHESS) method and short tau inversion recovery (STIR) method. MATERIALS AND METHODS Twenty-two healthy volunteers were examined using respiratory-triggered three-dimensional true steady-state free-precession with two time-spatial labeling inversion pulses. The CHESS or STIR methods were used for fat suppression. The relative signal-to-noise ratio and contrast-to-noise ratio (CNR) were quantified, and the quality of visualization was scored. RESULTS Image acquisition was successfully conducted in all volunteers. The STIR method significantly improved the CNRs of MR portography and hepatic venography. The image quality scores of main portal vein and right portal vein were higher with the STIR method, but there were no significant differences. The image quality scores of right hepatic vein, middle hepatic vein, and left hepatic vein (LHV) were all higher, and the visualization of LHV was significantly better (p<0.05). CONCLUSION The STIR method contributes to further suppression of the background signal and improves visualization of the portal and hepatic veins. The results support using non-contrast-enhanced MR portography and hepatic venography in clinical practice.

Quantitative CT analysis for the preoperative prediction of pathologic grade in pancreatic neuroendocrine tumors.

Pancreatic neuroendocrine tumors (PanNETs) account for approximately 5% of all pancreatic tumors, affecting one individual per million each year.1 PanNETs are difficult to treat due to biological variability from benign to highly malignant, indolent to very aggressive. The World Health Organization classifies PanNETs into three categories based on cell proliferative rate, usually detected using the Ki67 index and cell morphology: low-grade (G1), intermediate-grade (G2) and high-grade (G3) tumors. Knowledge of grade prior to treatment would select patients for optimal therapy: G1/G2 tumors respond well to somatostatin analogs and targeted or cytotoxic drugs whereas G3 tumors would be targeted with platinum or alkylating agents.2, 3 Grade assessment is based on the pathologic examination of the surgical specimen, biopsy or ne-needle aspiration; however, heterogeneity in the proliferative index can lead to sampling errors.4 Based on studies relating qualitatively assessed shape and enhancement characteristics on CT imaging to tumor grade in PanNET,5 we propose objective classification of PanNET grade with quantitative analysis of CT images. Fifty-five patients were included in our retrospective analysis. A pathologist graded the tumors. Texture and shape-based features were extracted from CT. Random forest and naive Bayes classifiers were compared for the classification of G1/G2 and G3 PanNETs. The best area under the receiver operating characteristic curve (AUC) of 0:74 and accuracy of 71:64% was achieved with texture features. The shape-based features achieved an AUC of 0:70 and accuracy of 78:73%.