FRET-assisted photoactivation of flavoproteins for in vivo two-photon optogenetics.

Optical dimerizers have been developed to untangle signaling pathways, but they are of limited use in vivo, partly due to their inefficient activation under two-photon (2P) excitation. To overcome this problem, we developed Förster resonance energy transfer (FRET)-assisted photoactivation, or FRAPA. On 2P excitation, mTagBFP2 efficiently absorbs and transfers the energy to the chromophore of CRY2. Based on structure-guided engineering, a chimeric protein with 40% FRET efficiency was developed and named 2P-activatable CRY2, or 2paCRY2. 2paCRY2 was employed to develop a RAF1 activation system named 2paRAF. In three-dimensionally cultured cells expressing 2paRAF, extracellular signal-regulated kinase (ERK) was efficiently activated by 2P excitation at single-cell resolution. Photoactivation of ERK was also accomplished in the epidermal cells of 2paRAF-expressing mice. We further developed an mTFP1-fused LOV domain that exhibits efficient response to 2P excitation. Collectively, FRAPA will pave the way to single-cell optical control of signaling pathways in vivo.

Optimization of prediction methods for risk assessment of pathogenic germline variants in the Japanese population.

Predicting pathogenic germline variants (PGVs) in breast cancer patients is important for selecting optimal therapeutics and implementing risk reduction strategies. However, PGV risk factors and the performance of prediction methods in the Japanese population remain unclear. We investigated clinicopathological risk factors using the Tyrer-Cuzick (TC) breast cancer risk evaluation tool to predict BRCA PGVs in unselected Japanese breast cancer patients (n = 1,995). Eleven breast cancer susceptibility genes were analyzed using target-capture sequencing in a previous study; the PGV prevalence in BRCA1, BRCA2, and PALB2 was 0.75%, 3.1%, and 0.45%, respectively. Significant associations were found between the presence of BRCA PGVs and early disease onset, number of familial cancer cases (up to third-degree relatives), triple-negative breast cancer patients under the age of 60, and ovarian cancer history (all P < .0001). In total, 816 patients (40.9%) satisfied the National Comprehensive Cancer Network (NCCN) guidelines for recommending multigene testing. The sensitivity and specificity of the NCCN criteria for discriminating PGV carriers from noncarriers were 71.3% and 60.7%, respectively. The TC model showed good discrimination for predicting BRCA PGVs (area under the curve, 0.75; 95% confidence interval, 0.69-0.81). Furthermore, use of the TC model with an optimized cutoff of TC score ≥0.16% in addition to the NCCN guidelines improved the predictive efficiency for high-risk groups (sensitivity, 77.2%; specificity, 54.8%; about 11 genes). Given the influence of ethnic differences on prediction, we consider that further studies are warranted to elucidate the role of environmental and genetic factors for realizing precise prediction.

Signal Intensity and Volume of Pituitary and Thyroid Glands in Preterm and Term Infants.

BACKGROUND: Hypothalamic-pituitary-thyroid (HPT) maturation has not been extensively evaluated using neonatal MRI, even though both structures are visualized on MRI. HYPOTHESIS: That signal intensity and volume of pituitary and thyroid (T) glands on MRI in neonates may be interrelated. STUDY TYPE: Retrospective. SUBJECTS: In all, 102 participants. FIELD STRENGTH/SEQUENCE: 3.0T, T1 -weighted pointwise encoding time reduction with radial acquisition (PETRA). ASSESSMENT: The volume of interest of the anterior pituitary (AP), posterior pituitary (PP), and T on MRI were defined on T1 -PETRA by two radiologists, and volumes of AP (AP_vol) and thyroid (T_vol) were calculated. Gestational age (GA), chronological age (CA), GA+CA, birth weight (BW), and thyroid function were recorded. Mean and maximum signal intensities of AP, PP, and T were normalized using signals from the pons and spinal cord as follows: signal ratio of anterior pituitary/pons (AP/pons), signal ratio of posterior pituitary/pons (PP/pons), and signal ratio of thyroid/cord (T/cord) T/cord, respectively. STATISTICAL TESTS: Correlations between signal intensity and volume measures and GA, CA, GA+CA, and BW were assessed using Pearson's correlation coefficient or Spearman's rank correlation coefficient. Thyroid function analysis and Tmean /cord, Tmax /cord, and T_vol were evaluated using the Steel-Dwass test. RESULTS: APmean /pons correlated positively with GA (ρ = 0.62, P < 0.001) and BW (ρ = 0.74, P < 0.001), and negatively with CA (ρ = -0.86, P < 0.001) and GA+CA (ρ = -0.46, P < 0.001). PPmean /pons correlated positively with GA (ρ = 0.49, P < 0.001) and BW (ρ = 0.63, P < 0.001), and negatively with CA (ρ = -0.70, P < 0.001) and GA+CA (r = -0.38, P < 0.001). Tmean /cord correlated positively with GA (ρ = 0.48, P < 0.001) and BW (ρ = 0.55, P < 0.001), and negatively with CA (ρ = -0.59, P < 0.001) and GA+CA (ρ = -0.22, P = 0.03). AP_vol correlated positively with GA (ρ = 0.68, P < 0.001) and BW (ρ = 0.73, P < 0.001), and negatively with CA (ρ = -0.72, P < 0.001). T_vol correlated positively with GA (ρ = 0.50, P < 0.001) and BW (ρ = 0.61, P < 0.001), and negatively with CA (ρ = -0.54, P < 0.001). APmean /pons correlated positively with Tmean /cord (ρ = 0.61, P < 0.001). DATA CONCLUSION: Signal and volume of pituitary and thyroid glands correlated positively with GA and BW, and negatively with CA in neonates. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY STAGE: 5.

Qualitative and Quantitative Assessment of Nonlocal Means Reconstruction Algorithm in a Flexible PET Scanner.

OBJECTIVE. Flexible PET (fxPET) was designed to fit existing MRI systems. The newly modified nonlocal means (NLM) algorithm is combined with the 3D dynamic row-action maximum likelihood algorithm (DRAMA). We investigated qualitative and quantitative acceptability of fxPET images reconstructed by modified NLM compared with whole-body (WB) PET/CT images and conventional 3D DRAMA reconstruction alone. MATERIALS AND METHODS. Fifty-nine patients with known or suspected malignancies underwent WB PET/CT scanning approximately 1 hour after the injection of 18F-FDG, after which they underwent fxPET scanning. Two readers rated the quality of fxPET images by consensus. Detection rate (the proportion of lesions found on PET), maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), tumor-to-normal liver ratio (TNR), and background liver signal-to-noise ratio (SNR) were compared among the three datasets. RESULTS. Higher image quality was obtained by modified NLM reconstruction than by conventional reconstruction without statistical significance. The detection rate was comparable among three datasets. SUVmax was significantly higher, and MTV and TLG were significantly lower in the modified NLM dataset (p < 0.002) than in the other two datasets, with significantly positive correlations (p < 0.001; Spearman rank correlation coefficient, 0.87-0.99). The TNRs in modified NLM images were significantly larger than in the other datasets (p < 0.05). The background SNRs in modified NLM images were comparable with those in WB PET/CT images, and significantly higher than in the conventional fxPET images (p < 0.005). CONCLUSION. The modified NLM algorithm was clinically acceptable, yielding higher TNR and background SNR compared with conventional reconstruction. Image quality and the lesion detection rate were comparable in this population.

Utility of real-time image fusion technology in ultrasonography-guided fiducial marker implantation for stereotactic body radiation therapy for liver tumors.

BACKGROUND: Ultrasonography (US) is useful when implanting fiducial markers in the liver. However, the implant position is sometimes lost. Recently, real-time image fusion technology (Volume Navigation [V-navi]; GE Healthcare, Milwaukee, WI, USA) has been introduced as a technique for using images from different modalities, and its utility for fiducial marker implantation has been hypothesized. PURPOSE: To evaluate the utility of US-guided fiducial marker implantation in the liver using V-navi compared to conventional US. MATERIAL AND METHODS: We retrospectively reviewed 35 patients who underwent fiducial marker implantation for stereotactic body radiation therapy of liver tumors in 2013-2018. To avoid artifacts obscuring the tumor, the target point of implantation was set 10 mm cranial or caudal to the tumor. Marker implantation was then performed using US alone (US group, n = 24) or V-navi with computed tomography (CT) or magnetic resonance imaging (V-navi group, n = 11). Postprocedural CT was evaluated to determine technical success, distances between marker and either tumor surface or target point, and whether marker-induced artifacts obscured the tumor. Complications were also evaluated. Results were compared between groups. RESULTS: Technical success was obtained in 33 patients. Distance between the tumor and marker showed no significant difference between groups. Distance between target point and marker was shorter in the V-navi group (P = 0.0093). Tumor-obscuring artifacts were seen in 12 patients (V-navi group, n = 1; US group, n = 11; P = 0.055). The only complication was minor bleeding in the US group (n = 1). CONCLUSION: V-navi appears useful for US-guided fiducial marker implantation in the liver compared with conventional US.

Diffusion-weighted imaging of uterine adenomyosis: Correlation with clinical backgrounds and comparison with malignant uterine tumors.

AIM: To elucidate correlation between signal intensity on diffusion-weighted images (SI-DWI) and clinical backgrounds for uterine adenomyosis and to compare SI-DWI of adenomyosis and malignant uterine tumors. METHODS: This study examined 46 adenomyosis patients diagnosed using magnetic resonance imaging and 25 patients with surgically confirmed malignant uterine myometrial tumor. First, adenomyosis cases were classified visually into high-intensity and low-intensity groups based on the SI-DWI compared with that of normal uterine myometrium. Secondly, correlation was assessed between SI-DWI of adenomyosis and patient clinical background information such as age, menopausal status, menstrual cycle and dysmenorrhea severity. Third, quantitative comparison was made of low-intensity adenomyosis (LIA), high-intensity adenomyosis (HIA) and malignant tumor groups for the signal intensity ratio (SIR) on DWI and the apparent diffusion coefficient (ADC). Their diagnostic performance was evaluated using logistic regression analysis and receiver operating characteristic (ROC) analysis. RESULTS: The 46 adenomyosis cases were classified as 26 low-intensity and 20 high-intensity cases. Significant correlation was found only for menstrual cycle phases. HIA had significantly lower SIR and higher ADC than malignant tumor. The ADC of HIA was significantly higher than that of LIA. The combination of SIR and ADC showed excellent diagnostic performance (area under ROC curve, 0.99). CONCLUSION: There is a variation in signal intensity on DWI of uterine adenomyosis and it is associated with menstrual cycle phase. Adenomyosis with high signal intensity on DWI can be differentiated from malignant lesions by its lower signal intensity on DWI and higher ADC than that found for malignant uterine tumors, however overlaps exist.

Brain MRI with Quantitative Susceptibility Mapping: Relationship to CT Attenuation Values.

Background Quantitative susceptibility mapping (QSM) is used to differentiate between calcification and iron deposits. Few studies have examined the relationship between CT attenuation values and magnetic susceptibility in such materials. Purpose To assess the relationship among metal concentration, CT attenuation values, and magnetic susceptibility in paramagnetic and diamagnetic phantoms, and the relationship between CT attenuation values and susceptibility in brain structures that have paramagnetic or diamagnetic properties. Materials and Methods In this retrospective study, CT and MRI with QSM were performed in gadolinium and calcium phantoms, patients, and healthy volunteers between June 2016 and September 2017. In the phantom study, we evaluated correlations among metal concentration, CT attenuation values, and susceptibility. In the human study, Pearson and Spearman correlations were performed to assess the relationship between CT attenuation values and susceptibility in regions of interest placed in the globus pallidus (GP), putamen, caudate nucleus, substantia nigra, red nucleus, dentate nucleus, choroid plexus, and hemorrhagic and calcified lesions. Results Eighty-four patients (mean age, 64.8 years ± 19.6; 49 women) and 20 healthy volunteers (mean age, 72.0 years ± 7.6; 11 men) were evaluated. In the phantoms, strong linear correlations were identified between gadolinium concentration and CT and MRI QSM values (R 2 = 0.95 and 0.99, respectively; P < .001 for both) and between calcium concentration and CT and MRI QSM values (R 2 = 0.89 [P = .005] and R 2 = 0.98 [P < .001], respectively). In human studies, positive correlations between CT attenuation values and susceptibility were observed in the GP (R 2 = 0.52, P < .001) and in hemorrhagic lesions (R 2 = 0.38, P < .001), and negative correlations were found in the choroid plexus (R 2 = 0.53, P < .001) and in calcified lesions (R 2 = 0.38, P = .009). Conclusion CT attenuation values showed a positive correlation with susceptibility in the globus pallidus and hemorrhagic lesions and negative correlation in the choroid plexus and calcified lesions. © RSNA, 2020 Online supplemental material is available for this article.

Diffusion MRI of the breast: Current status and future directions.

Diffusion-weighted imaging (DWI) is increasingly being incorporated into routine breast MRI protocols in many institutions worldwide, and there are abundant breast DWI indications ranging from lesion detection and distinguishing malignant from benign tumors to assessing prognostic biomarkers of breast cancer and predicting treatment response. DWI has the potential to serve as a noncontrast MR screening method. Beyond apparent diffusion coefficient (ADC) mapping, which is a commonly used quantitative DWI measure, advanced DWI models such as intravoxel incoherent motion (IVIM), non-Gaussian diffusion MRI, and diffusion tensor imaging (DTI) are extensively exploited in this field, allowing the characterization of tissue perfusion and architecture and improving diagnostic accuracy without the use of contrast agents. This review will give a summary of the clinical literature along with future directions. Level of Evidence: 5 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;52:70-90.

Evaluation of image quality of pituitary dynamic contrast-enhanced MRI using time-resolved angiography with interleaved stochastic trajectories (TWIST) and iterative reconstruction TWIST (IT-TWIST).

BACKGROUND: Time-resolved angiography with interleaved stochastic trajectories (TWIST) is a keyhole imaging with frequent sampling of central k-space data and view-sharing for the peripheral k-space of dynamic phases. IT-TWIST is a technique to reconstruct images with a smaller temporal footprint using the same raw data obtained with TWIST by iterative reconstruction. PURPOSE: To compare image quality between TWIST and IT-TWIST in 3D pituitary DCE-MRI. STUDY TYPE: Retrospective observation study. POPULATION: Fifty-one patients (23 men, 28 women) who underwent 3D pituitary DCE-MRI using TWIST between July 2016 and April 2017. FIELD STRENGTH/SEQUENCE: 3T/TWIST and IT-TWIST. ASSESSMENT: Visual evaluation was conducted for image quality of delineation of the pituitary stalk and posterior lobe during the early arterial phase, cerebral white matter near the sella turcica, and the mass lesion. Bolus sharpness of the pituitary stalk, posterior lobe, and bilateral cavernous sinus was evaluated on the enhancement slope map calculated from TWIST and IT-TWIST. Temporal stability of intensity of the nonenhanced area was evaluated on temporal standard deviation (SD) maps calculated from TWIST and IT-TWIST. STATISTICAL TESTS: Paired t-test or Wilcoxon rank-sum test was used to test the differences between TWIST and IT-TWIST in both visual evaluation and region of interest evaluation. RESULTS: Scores of visual evaluations for IT-TWIST were significantly better than those for TWIST (P < 0.001) in all items. Enhancement slope for IT-TWIST was significantly higher than that for TWIST in posterior lobe, and right and left cavernous sinus (P < 0.001). Temporal SD for IT-TWIST was significantly lower than that for TWIST in all items, with statistical significance (P < 0.001). DATA CONCLUSION: IT-TWIST yielded better visualization, and better enhancement slope, and less temporal SD compared with TWIST in 3D pituitary DCE-MRI. Evidence Level: 4 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:1497-1506.

New parameters of ultrafast dynamic contrast-enhanced breast MRI using compressed sensing.

BACKGROUND: Ultrafast dynamic contrast-enhanced (UF-DCE) breast MRI is considered a promising method of accelerated breast MRI. However, the value of new kinetic parameters derived from UF-DCE need clinical evaluation. PURPOSE: To evaluate the diagnostic performance of the maximum slope (MS), time to enhancement (TTE), and time interval between arterial and venous visualization (AVI) derived from UF-DCE MRI using compressed sensing (CS). STUDY TYPE: Retrospective. POPULATION: Seventy-five patients with histologically proven breast lesions. The total number of analyzed lesions was 90 (61 malignant and 29 benign). FIELD STRENGTH/SEQUENCE: 3T MRI with UF-DCE MRI based on the 3D gradient-echo volumetric interpolated breath-hold examination (VIBE) sequence using incoherent k-space sampling combined with a CS reconstruction followed by conventional DCE MRI. ASSESSMENT: The diagnostic performance of the MS, TTE, AVI, and conventional kinetic analysis was analyzed and compared with histology. STATISTICAL TESTS: Wilcoxon rank sum test, receiver operating characteristic analysis. RESULTS: The MS was larger and the TTE and AVI were smaller for malignant lesions compared with benign lesions: MS: 29.3%/s and 18.4%/s (P < 0.001), TTE: 7.0 and 12.0 seconds (P < 0.001), AVI: 2.7 and 4.4 frames (P = 0.006) for malignant and benign lesions. The discriminating power of the MS (area under the curve [AUC], 0.76) was slightly better than that of conventional kinetic analysis (AUC, 0.69) and comparable to that of the TTE and AVI (AUC, 0.78 and 0.76 for TTE and AVI, respectively). Invasive lobular carcinoma had smaller MS (21.8%/s) among malignant lesions (29.3%/s). DATA CONCLUSION: The MS, TTE, and AVI can be used to evaluate breast lesions with clinical performance equivalent to that of conventional kinetic analysis. These parameters vary among histologies. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:164-174.

Development of Novel PET Imaging Probes for Detection of Amylin Aggregates in the Pancreas.

The deposition of islet amyloid is associated with ß-cell mass dysfunction in type 2 diabetes mellitus (T2DM). Since the amylin aggregate is the main component of islet amyloid, in vivo imaging of amylin may be useful for diagnosis and elucidation of the pathogenic mechanism of T2DM. In the present study, we newly designed, synthesized, and evaluated two 18F labeled compounds ([18F]DANIR-F 2b and [18F]DANIR-F 2c) as positron emission tomography (PET) probes targeting amylin aggregates. In an in vitro binding study, DANIR-F 2b and DANIR-F 2c showed binding affinity for amylin aggregates (Ki = 160 and 29 nM, respectively). In addition, [18F]DANIR-F 2b and [18F]DANIR-F 2c clearly labeled islet amyloids in in vitro autoradiography of T2DM pancreatic sections. In the biodistribution study using normal mice, [18F]DANIR-F 2b and [18F]DANIR-F 2c displayed favorable pharamacokinetics in the pancreas and some organs located near the pancreas. Furthermore, in an ex vivo autoradiographic study, [18F]DANIR-F 2c also bound to amylin aggregates in the pancreas of the amylin transplanted mice. The results of this study suggest that [18F]DANIR-F 2c shows fundamental properties as a PET imaging probe targeting amylin aggregates in the T2DM pancreas.

Distinguishing intrahepatic mass-forming biliary carcinomas from hepatocellular carcinoma by computed tomography and magnetic resonance imaging using the Bayesian method: a bi-center study.

OBJECTIVES: To determine imaging hallmarks for distinguishing intrahepatic mass-forming biliary carcinomas (IMBCs) from hepatocellular carcinoma (HCC) and to validate their diagnostic ability using Bayesian statistics. METHODS: Study 1 retrospectively identified clinical and imaging hallmarks that distinguish IMBCs (n = 41) from HCC (n = 247) using computed tomography (CT) and magnetic resonance imaging (MRI). Study 2 retrospectively assessed the diagnostic ability of these hallmarks to distinguish IMBCs (n = 37) from HCC (n = 111) using Bayesian statistics with images obtained from a different institution. We also assessed the diagnostic ability of the hallmarks in the patient subgroup with high diagnostic confidence (≥ 80% of post-test probability). Two radiologists independently evaluated the imaging findings in studies 1 and 2. RESULTS: In study 1, arterial phase peritumoral parenchymal enhancement on CT/MRI, delayed enhancement on CT/MRI, diffusion-weighted imaging peripheral hyperintensity, and bile duct dilatation were hallmarks indicating IMBCs, whereas chronic liver disease, non-rim arterial phase hyperenhancement on CT/MRI, enhancing capsule on CT/MRI, and opposed-phase signal drop were hallmarks indicating HCC (p = 0.001-0.04). In study 2, Bayesian statistics-based post-test probability combining all hallmark features had a diagnostic accuracy of 89.2% (132/148) in distinguishing IMBCs from HCC for both readers. In the high diagnostic confidence subgroup (n = 120 and n = 124 for readers 1 and 2, respectively), the accuracy improved (95.0% (114/120) and 93.5% (116/124) for readers 1 and 2, respectively). CONCLUSIONS: Combined interpretation of CT and MRI to identify hallmark features is useful in discriminating IMBCs from HCCs. High post-test probability by Bayesian statistics allows for a more reliable non-invasive diagnosis. KEY POINTS: • Combined interpretation of CT and MRI to identify hallmark features was useful in discriminating intrahepatic mass-forming biliary carcinomas from hepatocellular carcinoma. • Bayesian method-based post-test probability combining all hallmark features determined in study 1 showed high (> 90%) sensitivity and specificity for distinguishing intrahepatic mass-forming biliary carcinomas from hepatocellular carcinoma. • If the post-test probability or the confidence was ≥ 80% when combining the imaging features of CT and MRI, the high specificity of > 95% was achieved without any loss of sensitivity to distinguish hepatocellular carcinoma from intrahepatic mass-forming biliary carcinomas.

Prognostic Value of Quantitative Parameters of 18F-FDG PET/CT for Patients With Angiosarcoma.

OBJECTIVE. The purpose of this study was to evaluate quantitative parameters in 18F-FDG PET/CT in terms of correlation with histologic grade and overall survival in patients with angiosarcoma. MATERIALS AND METHODS. The cases of 16 patients with histologically confirmed angiosarcoma who had undergone pretreatment FDG PET/CT were retrospectively analyzed. Maximum standardized uptake value for the primary tumor (pSUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) for the whole body, tumor-to-blood ratio (TBR) for the primary tumor, and summed ratios of tumor-to-blood glycolytic activity for all lesions (whole-body TLG ratio) were calculated. Tumors were divided into high grade and low grade, according to the pathologic results. Correlations between these metabolic parameters and tumor grade were investigated. The prognostic value of these parameters and various clinicopathologic factors with respect to overall survival was assessed with the Cox proportional hazards regression model. RESULTS. Histopathologic examination revealed 10 high-grade and six low-grade tumors. Among the quantitative parameters, pSUVmax (p < 0.0001) and primary TBR (p = 0.0003) were significantly higher for high-grade tumors than for low-grade tumors. Ten patients died during follow-up (median survival time, 19.6 months). Higher pSUVmax (p = 0.040), MTV (p = 0.016), whole-body TLG (p = 0.010), primary TBR (p = 0.019), and whole-body TLG ratio (p = 0.007) correlated significantly with poorer overall survival. Single lesion at initial diagnosis (p = 0.0008) and performance of curative surgery (p = 0.0008) were strong favorable prognostic factors for overall survival, but histologic grade was not identified as a significant predictor. CONCLUSION. In angiosarcoma, high-grade tumors had significantly higher pSUVmax and primary TBR at FDG PET/CT. All quantitative parameters evaluated in this study were found to be significant prognostic factors for overall survival.

Portal Vein Embolization: Radiological Findings Predicting Future Liver Remnant Hypertrophy.

OBJECTIVE. The purpose of this article is to evaluate the radiologic findings predicting the future liver remnant hypertrophy ratio after portal vein embolization of the right branch. MATERIALS AND METHODS. The associations between the radiologic findings and the future liver remnant hypertrophy ratio for 79 patients who underwent portal vein embolization of the right branch between July 2007 and April 2017 were retrospectively analyzed. Multiple linear regression was performed to adjust for potential confounders, and the volume ratio of the right lobe anterior segment, number of proximal small branches from the right anterior and posterior portal veins, transient hepatic parenchymal enhancement, portal vein invasion, and variants of main portal vein anatomy were evaluated. The potential confounders were age, ratio of future liver remnant hypertrophy to total liver volume, indocyanine green clearance rate, maximum serum total bilirubin before portal vein embolization, and history of chemotherapy. RESULTS. Statistically significant associations were found between the future liver remnant hypertrophy ratio and the number of proximal small branches from the right anterior and posterior portal veins (p < 0.001), transient hepatic parenchymal enhancement (p < 0.001), portal vein invasion (p = 0.017), and variants of main portal vein anatomy (p = 0.048). The mean future liver remnant hypertrophy rate was 51.0% (n = 16) in patients without the radiologic findings showing statistically significant differences, and 25.8% (n = 63) in patients with at least one significant finding. CONCLUSION. When added to previously reported factors, the radiologic findings identified can help determine the indications for portal vein embolization and novel strategies for major hepatectomy.

Imaging of Pancreaticobiliary Maljunction.

Pancreaticobiliary maljunction (PBM) is a congenital malformation in which the pancreatic and bile ducts join outside the duodenal wall, usually forming a long common channel. A major issue in patients with PBM is the risk of biliary cancer. Because the sphincter of Oddi does not regulate the pancreaticobiliary junction in PBM, pancreatic juice frequently refluxes into the biliary tract and can cause various complications, including biliary cancer. Most cancers arise in the gallbladder or dilated common bile duct, suggesting that bile stasis is related to carcinogenesis. Early diagnosis and prophylactic surgery to reduce the risk of cancer are beneficial. The diagnosis of PBM is made mainly on the basis of imaging findings. The development of diagnostic imaging modalities such as multidetector CT and MR cholangiopancreatography has provided radiologists with an important role in diagnosis of PBM and its complications. Radiologists should be aware of PBM despite the fact that it is rare in non-Asian populations. In this review, the authors present an overview of PBM with emphasis on diagnosis and management of PBM and its complications. For early diagnosis, the presence of extrahepatic bile duct dilatation or gallbladder wall thickening may provide a clue to PBM with or without biliary dilatation, respectively. The pancreaticobiliary anatomy should be closely examined if imaging reveals these findings. Radiologists should also carefully evaluate follow-up images in PBM patients even years after prophylactic surgery because residual bile ducts remain at risk for cancer.©RSNA, 2020.

Acceleration of 2D-MR fingerprinting by reducing the number of echoes with increased in-plane resolution: a volunteer study.

OBJECTIVE: To compare the absolute values and repeatability of magnetic resonance fingerprinting (MRF) with 3000 and 1500 echoes/slice acquired in 41 s and 20 s (MRF3k and MRF1.5k, respectively). MATERIALS AND METHODS: MRF3k and MRF1.5k scans based on fast imaging with steady precession (FISP) were conducted using a 3 T scanner. Inter-scan agreement and intra-scan repeatability were investigated in 41 and 28 subjects, respectively. Region-of-interest (ROI) analysis was conducted on T1 values of MRF3k by two raters, and their agreement was evaluated using intraclass correlation coefficients (ICCs). Between MRF3k and MRF1.5k, differences in T1 and T2 values and inter-measurement correlation coefficients (CCs) were investigated. Intra-measurement repeatability was evaluated using coefficients of variation (CVs). A p value < 0.05 was considered statistically significant. RESULTS: The ICCs of ROI measurements were 0.77-0.96. Differences were observed between the two MRF scans, but the CCs of the overall ROIs were 0.99 and 0.97 for the T1 and T2 values, respectively. The mean and median CVs of repeatability were equal to or less than 1.58% and 3.13% in each of the ROIs for T1 and T2, respectively; there were some significant differences between MRF3k and MRF1.5k, but they were small, measuring less than 1%. DISCUSSION: Both MRF3k and MRF1.5k had high repeatability, and a strong to very strong correlation was observed, with a trend toward slightly higher values in MRF1.5k.

Adaptive Voxel Matching for Temporal CT Subtraction.

Temporal subtraction (TS) technique calculates a subtraction image between a pair of registered images acquired from the same patient at different times. Previous studies have shown that TS is effective for visualizing pathological changes over time; therefore, TS should be a useful tool for radiologists. However, artifacts caused by partial volume effects degrade the quality of thick-slice subtraction images, even with accurate image registration. Here, we propose a subtraction method for reducing artifacts in thick-slice images and discuss its implementation in high-speed processing. The proposed method is based on voxel matching, which reduces artifacts by considering gaps in discretized positions of two images in subtraction calculations. There are two different features between the proposed method and conventional voxel matching: (1) the size of a searching region to reduce artifacts is determined based on discretized position gaps between images and (2) the searching region is set on both images for symmetrical subtraction. The proposed method is implemented by adopting an accelerated subtraction calculation method that exploit the nature of liner interpolation for calculating the signal value at a point among discretized positions. We quantitatively evaluated the proposed method using synthetic data and qualitatively using clinical data interpreted by radiologists. The evaluation showed that the proposed method was superior to conventional methods. Moreover, the processing speed using the proposed method was almost unchanged from that of the conventional methods. The results indicate that the proposed method can improve the quality of subtraction images acquired from thick-slice images.

Initial evaluation of PET/CT with 18 F-FSU-880 targeting prostate-specific membrane antigen in prostate cancer patients.

This first-in-man study was carried out to evaluate the safety, whole-body distribution, dose estimation, and lesion accumulation of 18 F-FSU-880, a newly developed probe targeting prostate-specific membrane antigen. Six prostate cancer patients with known metastatic lesions underwent serial whole-body PET/computed tomography (CT) with 18 F-FSU-880. Blood and urine were analyzed before and after PET/CT. Accumulation of 18 F-FSU-880 in organs and metastatic lesions in serial PET images were evaluated by measuring the standardized uptake values. From the biodistribution data, the organ doses and whole-body effective dose were calculated using OLINDA/EXM software was developed by Dr. Michael Stabin of Vanderbilt University, Nashville, Tennessee, USA. 18 F-FSU-880 PET/CT could be carried out without significant adverse effects. High physiological uptake was observed in the salivary/lachrymal glands and kidneys. The effective dose was calculated to be 0.921 × 10-2 mSv/MBq. Known metastatic lesions were clearly visualized with high image contrast that increased with time, except in 1 patient, whose bone metastases were well-controlled and inactive. The PET/CT with 18 F-FSU-880 could be carried out safely and could clearly visualize active metastatic lesions. The present results warrant further clinical studies with a larger number of cases to verify the clinical utility of 18 F-FSU-880 PET/CT in the management of prostate cancer patients.

Clinical utility of 68Ga-DOTATOC positron emission tomography/computed tomography for recurrent renal cell carcinoma.

PURPOSE: Positron emission tomography (PET)/computed tomography (CT) with 68Ga-labelled 1,4,7,10-tetraazacyclododecane-N,N',N″,N″'-tetraacetic acid-D-Phe1-Tyr3-octreotide (DOTATOC) has been accepted as a diagnostic imaging tool especially for patients with neuroendocrine tumours. However, its clinical usefulness for restaging of renal cell carcinoma (RCC) has not been fully investigated. This retrospective study was performed to elucidate the clinical value of PET/CT using 68Ga-DOTATOC in patients with known or suspected recurrent RCC. METHODS: We analysed 25 consecutive patients who underwent DOTATOC-PET/CT scans after surgery for RCC (23 clear cell, 1 papillary, 1 unclassified). PET/CT findings were reviewed and the detection rate was calculated on a patient and lesion basis. The detectability was compared in patients who also underwent PET/CT scans with 18F-fluorodeoxyglucose (FDG). Histopathological findings or clinical follow-up were used as the reference standard. RESULTS: Based on the final diagnosis, 76 recurrent or metastatic lesions were confirmed in this population. Of these lesions, 66 lesions in 22 patients were positive by DOTATOC-PET/CT. The patient-based and lesion-based sensitivity was 88% (22/25) and 87% (66/76), respectively. Twelve patients underwent both DOTATOC-PET/CT and FDG-PET/CT. The lesion-based sensitivity of DOTATOC was 74% (20/27), while that of FDG was 59% (16/27). Eight lesions were identified only by DOTATOC, but four lesions from papillary RCC were detected only by FDG. CONCLUSION: Our data indicate that DOTATOC-PET/CT would be useful for detecting recurrent foci in patients with clear cell RCC. DOTATOC-PET/CT and FDG-PET/CT are considered to have complementary roles.

Time-dependent diffusion MRI to distinguish malignant from benign head and neck tumors.

BACKGROUND: There is growing interest in the effect of diffusion time on apparent diffusion coefficient (ADC) values in cancers; however, little evidence exists regarding its utility to differentiate malignant from benign head and neck tumors. PURPOSE: To investigate the utility of ADC value changes in distinguishing between malignant and benign head and neck tumors using the different diffusion times obtained from oscillating gradient spin-echo (OGSE) and pulsed gradient spin-echo (PGSE) MRI sequences. STUDY TYPE: Prospective. SUBJECTS: Thirty-one consecutive patients with suspected head and neck tumors and a phantom. FIELD STRENGTH/SEQUENCE: 3T MRI with diffusion-weighted imaging (DWI) using OGSE (effective diffusion time: 4.3 msec) and PGSE (effective diffusion time: 82.6 msec) sequences and b-values of 0 and 700 s/mm2 . ASSESSMENT: ADC values using OGSE (ADCOGSE ) and PGSE (ADCPGSE ) and relative ADC value changes between ADCOGSE and ADCPGSE . STATISTICAL TESTS: Wilcoxon test, Mann-Whitney test, and McNemar test. RESULTS: Relative ADC changes for each polyvinylpyrrolidone (PVP) and water in the phantom between OGSE and PGSE sequences were small (relative ADC change within 0.6%). Malignant tumors had significantly smaller ADCOGSE and ADCPGSE values than benign tumors (P < 0.001 and < 0.0001, respectively). Significantly larger relative ADC changes were observed in malignant compared with benign head and neck tumors (P < 0.0001). ADCPGSE values were significantly lower than ADCOGSE values in both malignant and benign head and neck tumors (0.97 vs. 1.28 × 10-3 mm2 /s: P < 0.0001 and 1.93 vs. 1.99 × 10-3 mm2 /s: P = 0.0056, respectively). Relative ADC change and ADCPGSE tended to have higher diagnostic performance than ADCOGSE , with area under the curve (AUC) values of 0.97, 0.96, and 0.89, respectively. DATA CONCLUSION: ADC values obtained using the PGSE sequence were lower than those obtained with OGSE. This difference was larger for malignant than benign tumors, suggesting differences in tissue structure (diffusion hindrance) or cell permeability, revealed by changes in diffusion time. The results underline the potential importance of reporting diffusion time for interpretation of head and neck diffusion MRI. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:88-95.