Liver volumetry and liver-regenerative interventions: history, rationale, and emerging tools.

BACKGROUND: Postoperative hepatic insufficiency (PHI) is the most feared complication after hepatectomy. Volume of the future liver remnant (FLR) is one objectively measurable indicator to identify patients at risk of PHI. In this review, we summarized the development and rationale for the use of liver volumetry and liver-regenerative interventions and highlighted emerging tools that could yield new advancements in liver volumetry. METHODS: A review of MEDLINE/PubMed, Embase, and Cochrane Library databases was conducted to identify literature related to liver volumetry. The references of relevant articles were reviewed to identify additional publications. RESULTS: Liver volumetry based on radiologic imaging was developed in the 1980s to identify patients at risk of PHI and later used in the 1990s to evaluate grafts for living donor living transplantation. The field evolved in the 2000s by the introduction of standardized FLR based on the hepatic metabolic demands and in the 2010s by the introduction of the degree of hypertrophy and kinetic growth rate as measures of the FLR regenerative and functional capacity. Several liver-regenerative interventions, most notably portal vein embolization, are used to increase resectability and reduce the risk of PHI. In parallel with the increase in automation and machine assistance to physicians, many semi- and fully automated tools are being developed to facilitate liver volumetry. CONCLUSION: Liver volumetry is the most reliable tool to detect patients at risk of PHI. Advances in imaging analysis technologies, newly developed functional measures, and liver-regenerative interventions have been improving our ability to perform safe hepatectomy.

Arterial enhancement pattern predicts survival in patients with resectable and unresectable intrahepatic cholangiocarcinoma.

BACKGROUND: In patients undergoing resection of intrahepatic cholangiocarcinoma (ICC), hypervascularity during the arterial phase of contrast-enhanced computed tomography (CT) is associated with better prognosis than hypovascularity. However, the prognostic implications of arterial enhancement pattern in patients with unresectable ICC are unknown. We assessed the prognostic implications of arterial enhancement pattern in patients with resectable and unresectable ICC. METHODS: Consecutive patients who underwent surgery or gemcitabine-plus-cisplatin chemotherapy for ICC during 2003-2015 and CT with dynamic enhancement for diagnosis were included. After review by 2 radiologists, tumors were categorized according to the percentage of the tumor exhibiting arterial enhancement as hypervascular (>50% of tumor exhibiting enhancement), peripherally enhancing (10%-50%), and hypovascular (<10%). In each cohort (surgical and medical), overall survival (OS) curves were generated using the Kaplan-Meier method, and differences between curves were evaluated with Cox analysis. RESULTS: The study included 56 patients treated surgically and 89 patients with unresectable ICC. Mean (standard deviation) tumor density in the hypervascular, peripherally enhancing, and hypovascular groups was 119.3 (45.2) Hounsfield units (HU), 72.1 (15.9) HU, and 59.9 (14.4) HU, respectively, in the surgical cohort and 93.6 (17.5) HU, 66.6 (16.2) HU, and 48.7 (14.3) HU, respectively, in the medical cohort. In both cohorts, the 5-year OS rate was significantly higher in the hypervascular group than in the hypovascular group (surgical, 67.6% vs 22.5%, P = .038; medical, 15.4% vs 0%, P = .030). In both cohorts, a Cox proportional hazards model analysis showed that hypervascularity was significantly associated with better OS. CONCLUSION: Hypervascularity during the arterial CT phase is a prognostic biomarker in patients undergoing ICC resection and patients with unresectable ICC.

Lynch Syndrome: Genomics Update and Imaging Review.

Lynch syndrome is the most common hereditary cancer syndrome, the most common cause of heritable colorectal cancer, and the only known heritable cause of endometrial cancer. Other cancers associated with Lynch syndrome include cancers of the ovary, stomach, urothelial tract, and small bowel, and less frequently, cancers of the brain, biliary tract, pancreas, and prostate. The oncogenic tendency of Lynch syndrome stems from a set of genomic alterations of mismatch repair proteins. Defunct mismatch repair proteins cause unusually high instability of regions of the genome called microsatellites. Over time, the accumulation of mutations in microsatellites and elsewhere in the genome can affect the production of important cellular proteins, spurring tumorigenesis. Universal testing of colorectal tumors for microsatellite instability (MSI) is now recommended to (a) prevent cases of Lynch syndrome being missed owing to the use of clinical criteria alone, (b) reduce morbidity and mortality among the relatives of affected individuals, and (c) guide management decisions. Organ-specific cancer risks and associated screening paradigms vary according to the sex of the affected individual and the type of germline DNA alteration causing the MSI. Furthermore, Lynch syndrome-associated cancers have different pathologic, radiologic, and clinical features compared with their sporadic counterparts. Most notably, Lynch syndrome-associated tumors tend to be more indolent than non-Lynch syndrome-associated neoplasms and thus may respond differently to traditional chemotherapy regimens. The high MSI in cases of colorectal cancer reflects a difference in the biologic features of the tumor, possibly with a unique susceptibility to immunotherapy. ©RSNA, 2018.

MRI assessment of early tumor response in metastatic renal cell carcinoma patients treated with sorafenib.

OBJECTIVE: The purpose of this study was to examine early MRI changes in renal cell carcinoma (RCC) treated with the antiangiogenic agent sorafenib and to identify MRI biomarkers of RCC response to sorafenib. MATERIALS AND METHODS: Sixteen patients with RCC were evaluated by MRI before and 3-12 weeks after commencing treatment with sorafenib. Two experienced MR radiologists, blinded to treatment status, independently graded tumor appearance on T1-weighted, T2-weighted, and gadolinium-enhanced images. The proportional odds mixed model was used to compare qualitative appearance of tumors before and after therapy. Time-to-progression was correlated with Response Evaluation Criteria in Solid Tumors (RECIST) 1.0 and MR-modified Choi criteria, incorporating changes in both tumor enhancement and size. RESULTS: After sorafenib therapy, there was a significant increase in T1 signal intensity of tumors (p < 0.0001) and a significant decrease in degree of tumor enhancement (p < 0.0001). The sum of unidimensional tumor diameters decreased significantly after therapy (p = 0.005). However, the average decrease in size at early follow-up was 13%, and all patients except one had stable disease by RECIST 1.0. Early responders defined by MR-modified Choi criteria had increased time-to-progression compared with nonresponders, whereas early RECIST evaluation did not predict clinical outcome. CONCLUSION: Decreased enhancement and T1 shortening of tumors on MRI may be useful biomarkers of RCC response to angiogenesis inhibitors. Response criteria combining early changes in size and enhancement lead to better correlation with clinical outcome compared with size decrease alone.

Using focused missed-case conferences to reduce discrepancies in musculoskeletal studies interpreted by residents on call.

OBJECTIVE: The purpose of this study is to determine whether focused missed-case conferences can significantly reduce the number of major discrepancies in musculoskeletal imaging studies interpreted by residents on call. MATERIALS AND METHODS: A review of major discrepancies in musculoskeletal conventional radiography imaging studies interpreted by radiology residents and fellows on call from July 2008 to July 2009 revealed 31 common and important musculoskeletal injuries missed or misinterpreted at our institution. These missed cases were presented during focused missed-case conferences from July through October 2009. Only residents attended missed-case conferences. RESULTS: Over the 12 months before the missed-case conferences, there were 55 resident major discrepancies and 25 fellow major discrepancies, representing 31 common and important missed musculoskeletal injuries. Over the 12 months after the missed-case conferences, there were 18 resident major discrepancies and 21 fellow major discrepancies involving these injuries. This corresponds to a 67% reduction in the number of resident major discrepancies involving the 31 musculoskeletal injuries covered during the missed-case conferences (chi-square p < 0.001). The overall major discrepancy rate for all musculoskeletal conventional radiography studies was 1.19% for residents and 1.55% for fellows (not significant) before the missed-case conferences and 0.87% for residents and 1.46% for fellows (p < 0.05) after the missed-case conferences. During this time, fellows missed more musculoskeletal injuries related to the topics discussed during missed-case conferences (16) compared with residents (8) although fellows read significantly fewer studies overall. This accounted for 0.49% of the 0.59% difference between residents and fellows. CONCLUSION: Focused missed-case conferences are an effective educational intervention to significantly reduce the number of major discrepancies in radiology resident interpretation of musculoskeletal imaging studies on call.

Comparison of functional activation foci in children and adults using a common stereotactic space.

The development of methods allowing direct comparisons between child and adult neuroimaging data is an important prerequisite for studying the neural bases of cognitive development. Several issues arise when attempting to make such direct comparisons, including the comparability of anatomical localization of functional responses and the magnitude and time course of the hemodynamic responses themselves. Previous results suggest that, after transformation into a common stereotactic space, anatomical differences between children (ages 7 and 8) and adults are small relative to the resolution of fMRI data. Here, we investigate whether time courses (BOLD responses) and locations of functional activation foci show similarities as well. Event-related fMRI was performed on 16 children (ages 7 and 8) and 16 adults, who pressed buttons in response to a visual stimulus. After transforming images into Talairach space, the coordinates of four consistent activations in each hemisphere were determined for each subject: two foci in the sensorimotor cortex, one focus in the visual cortex, and one focus in the supplementary motor area (eight activations in total). In seven foci, time courses were similar between children and adults, and peak amplitudes of time courses were comparable in all eight foci. There were negligible between-group differences in location of all foci. Variability of activation location was statistically similar in the two groups. In voxelwise group comparison images, minimal differences were found between children and adults in visual and motor cortex regions. The small differences in time courses and locations of activation foci between child and adult brains validate the feasibility of direct statistical comparison of these groups within a common space.

Measurement of cerebral blood flow in chronic carotid occlusive disease: comparison of dynamic susceptibility contrast perfusion MR imaging with positron emission tomography.

BACKGROUND AND PURPOSE: Our purpose was to evaluate the accuracy of cerebral blood flow (CBF) measurements obtained by using dynamic susceptibility contrast-enhanced MR imaging, including the influence of arterial input function (AIF) selection, compared with those obtained by using [(15)O]-H(2)O positron emission tomography (PET) for patients with chronic carotid occlusion. METHODS: MR images and PET scans were obtained of seven patients with unilateral carotid occlusion and were co-registered for region of interest analysis. PET CBF maps were generated by using the autoradiographic method. MR imaging CBF maps were calculated by deconvolution of the susceptibility time curve with a proximal middle cerebral artery AIF and were converted to absolute flow rates either by assuming a constant contralateral white matter CBF value of 22 mL/100 mL/min or by using individually determined PET white matter CBF values. RESULTS: Although CBF values measured by PET and MR imaging were positively correlated for every patient, the slopes and y intercepts of the regression lines varied widely among patients. The correlation was better when individual white matter CBF values measured by PET were used to scale the white matter CBF values measured by MR imaging (r = 0.84, P <.0001) than when constant contralateral CBF values were assumed (r = 0.54, P <.0001). The choice of AIF ipsilateral or contralateral to the occluded carotid artery made no statistically significant difference (P >.05) to the correlation coefficient, slope, or y intercept of the MR imaging versus PET CBF regressions for six of the seven patients. CONCLUSION: Although linearly correlated with CBF values measured by PET, dynamic susceptibility contrast-enhanced MR imaging was not accurate for measuring absolute CBF values. AIF selection relative to the side of carotid occlusion did not significantly affect calculated MR imaging CBF values for six of the seven patients.

The feasibility of a common stereotactic space for children and adults in fMRI studies of development.

The question of whether pediatric and adult neuroimaging data can be analyzed in a common stereotactic space is a critical issue for developmental neuroscience. Two studies were performed to address this question. In Study 1, high-resolution structural MR brain images of 20 children (7-8 years of age) and 20 young adults (18-30 years of age) were transformed to a common space. Overall brain shape was assessed by tracing the outer boundaries of the brains in three orientations, and more local anatomy was assessed by analysis of portions of 10 selected sulci. Small, but consistent, differences in location and variability were observed in specific locations of the sulcal tracings and outer-boundary sections. In Study 2, a computer simulation was used to assess the extent to which the small anatomical differences observed in Study 1 would produce spurious effects in functional imaging data. Results indicate that, assuming a functional resolution of 5 mm in images averaged across subjects, anatomical differences in either variability or location between children and adults of the magnitude obperved in Study 1 would not negatively affect functional image comparisons. We conclude that atlas-transformed brain morphology is relatively consistent between 7- and 8-year-old children and adults at a resolution appropriate to current functional imaging and that the small anatomical differences present do not limit the usefulness of comparing child and adult functional images within a common stereotactic space.