Vessel territory mapping after cerebral revascularization surgery using selective angiographic flat detector perfusion imaging.

The technical feasibility and diagnostic potential of angiographic flat-detector perfusion imaging technique, combining digital subtraction angiography with a flat-detector computed tomography steady-state perfusion imaging, was explored in patients treated with direct or indirect revascularization surgery. This short communication is about an imaging modality with great potential for evaluation, comparison and grading of vascular perfusion territory areas and anatomical location selectively perfused by direct and indirect cerebral bypasses.

Can indocyanine green perfusion imaging detect microangiopathy in mastectomy skin flaps?

Intraoperative vascular imaging using indocyanine green (ICG) angiography may better predict flap viability than clinical judgement alone. Intraoperative ICG angiography was used in a chronic corticosteroid user undergoing bilateral nipple sparing mastectomy with expander placement. Large blood vessels were visualized, however, the skin surrounding these vessels remained dark. The flap demarcated to full-thickness necrosis that matched the intraoperative SPY findings. Visualization of intact blood vessels may not be sufficient to rule out flap necrosis in some patients. In these circumstances, interpretation of perfusion with consideration of patient factors will be required to accurately predict flap viability.

Does perfusion computed tomography correlate to pathology in colorectal liver metastases?

INTRODUCTION: Targeted therapy against tumor angiogenesis is widely used in clinical practice for patients with colorectal liver metastases (CRLM). Possible predictive biomarkers for tumor angiogenesis, such as, microvessel density (MVD), hypoxia and cell proliferation, can be determined using immunohistochemical staining. However, patients ineligible for surgical treatment need to undergo invasive diagnostic interventions in order to determine these biomarkers. CT perfusion (CTP) is an emerging functional imaging technique, which can non-invasively determine vascular properties of solid tumors. The purpose of this study was to evaluate CTP with histological biomarkers in CRLM. MATERIAL AND METHODS: Patients with CRLM underwent CTP one day before liver surgery. CTP analysis was performed on the entire volume of the largest metastases in each patient. Dual-input maximum slope analysis was used and data concerning arterial flow (AF), portal flow (PF) and perfusion index (PI) were recorded. Immunohistochemical staining with CD34, M75/CA-IX and MIB-1 was performed on the rim in the midsection of the tumor to determine respectively MVD, hypoxia and cell proliferation. RESULTS: Twenty CRLM in 20 patients were studied. Mean size of the largest CRLM was 37 mm (95% CI 21-54 mm). Mean AF and PF were respectively 64 ml/min/100ml (95% CI 48-79) and 30 ml/min/100ml (95% CI 22-38). Mean PI was 68% (95% CI 62-73). No significant correlation was found between tumor growth patterns and CTP (p = 0.95). MVD did not significantly correlate to AF (r = 0.05; p = 0.84), PF (r = 0.17; p = 0.47) and PI (r = -0.12; p = 0.63). Cell proliferation also did not significantly correlate to AF (r = 0.07; p = 0.78), PF (r = -0.01; p = 0.95) and PI (r = 0.15; p = 0.52). Hypoxia did not significantly correlate to AF (r = -0.05; p = 0.83), however, significantly to PF (r = 0.51; p = 0.02) and a trend to negative correlation with PF (r = -0.43; p = 0.06). However, after controlling the false discovery rate, no significant correlation between CTP and used immunohistochemical biomarkers was found. CONCLUSION: In conclusion, this feasibility study found a trend to negative correlation between PI and hypoxia, CTP might therefore possibly evaluate this prognostic marker in CRLM non-invasively. However, CTP is not an appropriate technique for the assessment of microvessels or cell proliferation in CRLM.

Assessment of computed tomography perfusion software in predicting spatial location and volume of infarct in acute ischemic stroke patients: a comparison of Sphere, Vitrea, and RAPID.

BACKGROUND: CT perfusion (CTP) infarct and penumbra estimations determine the eligibility of patients with acute ischemic stroke (AIS) for endovascular intervention. This study aimed to determine volumetric and spatial agreement of predicted RAPID, Vitrea, and Sphere CTP infarct with follow-up fluid attenuation inversion recovery (FLAIR) MRI infarct. METHODS: 108 consecutive patients with AIS and large vessel occlusion were included in the study between April 2019 and January 2020 . Patients were divided into two groups: endovascular intervention (n=58) and conservative treatment (n=50). Intervention patients were treated with mechanical thrombectomy and achieved successful reperfusion (Thrombolysis in Cerebral Infarction 2b/2 c/3) while patients in the conservative treatment group did not receive mechanical thrombectomy or intravenous thrombolysis. Intervention and conservative treatment patients were included to assess infarct and penumbra estimations, respectively. It was assumed that in all patients treated conservatively, penumbra converted to infarct. CTP infarct and penumbra volumes were segmented from RAPID, Vitrea, and Sphere to assess volumetric and spatial agreement with follow-up FLAIR MRI. RESULTS: Mean infarct differences (95% CIs) between each CTP software and FLAIR MRI for each cohort were: intervention cohort: RAPID=9.0±7.7 mL, Sphere=-0.2±8.7 mL, Vitrea=-7.9±8.9 mL; conservative treatment cohort: RAPID=-31.9±21.6 mL, Sphere=-26.8±17.4 mL, Vitrea=-15.3±13.7 mL. Overlap and Dice coefficients for predicted infarct were (overlap, Dice): intervention cohort: RAPID=(0.57, 0.44), Sphere=(0.68, 0.60), Vitrea=(0.70, 0.60); conservative treatment cohort: RAPID=(0.71, 0.56), Sphere=(0.73, 0.60), Vitrea=(0.72, 0.64). CONCLUSIONS: Sphere proved the most accurate in patients who had intervention infarct assessment as Vitrea and RAPID overestimated and underestimated infarct, respectively. Vitrea proved the most accurate in penumbra assessment for patients treated conservatively although all software overestimated penumbra.

Perfusion weighted imaging using combined gradient/spin echo EPIK: Brain tumour applications in hybrid MR-PET.

Advanced perfusion-weighted imaging (PWI) methods that combine gradient echo (GE) and spin echo (SE) data are important tools for the study of brain tumours. In PWI, single-shot, EPI-based methods have been widely used due to their relatively high imaging speed. However, when used with increasing spatial resolution, single-shot EPI methods often show limitations in whole-brain coverage for multi-contrast applications. To overcome this limitation, this work employs a new version of EPI with keyhole (EPIK) to provide five echoes: two with GEs, two with mixed GESE and one with SE; the sequence is termed "GESE-EPIK." The performance of GESE-EPIK is evaluated against its nearest relative, EPI, in terms of the temporal signal-to-noise ratio (tSNR). Here, data from brain tumour patients were acquired using a hybrid 3T MR-BrainPET scanner. GESE-EPIK resulted in reduced susceptibility artefacts, shorter TEs for the five echoes and increased brain coverage when compared to EPI. Moreover, compared to EPI, EPIK achieved a comparable tSNR for the first and second echoes and significantly higher tSNR for other echoes. A new method to obtain multi-echo GE and SE data with shorter TEs and increased brain coverage is demonstrated. As proposed here, the workflow can be shortened and the integration of multimodal clinical MR-PET studies can be facilitated.

Response assessment in paediatric low-grade glioma: recommendations from the Response Assessment in Pediatric Neuro-Oncology (RAPNO) working group.

Paediatric low-grade gliomas (also known as pLGG) are the most common type of CNS tumours in children. In general, paediatric low-grade gliomas show clinical and biological features that are distinct from adult low-grade gliomas, and the developing paediatric brain is more susceptible to toxic late effects of the tumour and its treatment. Therefore, response assessment in children requires additional considerations compared with the adult Response Assessment in Neuro-Oncology criteria. There are no standardised response criteria in paediatric clinical trials, which makes it more difficult to compare responses across studies. The Response Assessment in Pediatric Neuro-Oncology working group, consisting of an international panel of paediatric and adult neuro-oncologists, clinicians, radiologists, radiation oncologists, and neurosurgeons, was established to address issues and unique challenges in assessing response in children with CNS tumours. We established a subcommittee to develop consensus recommendations for response assessment in paediatric low-grade gliomas. Final recommendations were based on literature review, current practice, and expert opinion of working group members. Consensus recommendations include imaging response assessments, with additional guidelines for visual functional outcomes in patients with optic pathway tumours. As with previous consensus recommendations, these recommendations will need to be validated in prospective clinical trials.

Towards 4D dedicated breast CT perfusion imaging of cancer: development and validation of computer simulated images.

Dedicated breast CT is a fully tomographic breast imaging modality with potential for various applications throughout breast cancer care. If implemented to perform dynamic contrast-enhanced (CE) imaging (4D breast CT), it could be useful to obtain functional information at high combined spatio-temporal resolution. Before developing a 4D dedicated breast CT system, a computer simulation method for breast CT perfusion imaging is proposed. The simulation uses previously developed patient-based 4D digital breast phantoms, and generates realistic images with the selected acquisition parameters, allowing to investigate the effect of different acquisition settings on image quality. The simulation pipeline includes all steps of the image generation process, from ray tracing and scatter map generation, to the addition of realistic resolution losses and noise models. The pipeline was validated against experimental measurements performed on physical phantoms with a dedicated breast CT system, in terms of average error compared to ground truth projections (6.0% ± 1.65%), Hounsfield unit (HU) values in a homogeneous phantom (acquired: -149 HU ± 2 HU; simulated: -140 HU ± 2 HU), signal-to-noise ratio (SNR) (average error 6.7% ± 4.2%), noise power spectra (NPS) (average error 4.3% ± 2.5%), modulation transfer function (MTF) (average error 8.4% ± 7.2%), and attenuation of different adipose/glandular equivalent mixtures (average error 6.9% ± 4.0%) and glandular plus iodinated contrast medium concentrations equivalent mixtures (average error of 9.1% ± 9.0%). 4D patient images were then simulated for different 4D digital breast phantoms at different air kerma levels to determine the effect of noise on the extracted tumor perfusion curves. In conclusion, the proposed pipeline could simulate images with a good level of realism, resulting in a tool that can be used for the design, development, and optimization of a 4D dedicated breast CT system.

Hyperspectral imaging for noninvasive tissue perfusion measurements of the lower leg: review of literature and introduction of a standardized measurement protocol with a portable system.

INTRODUCTION: Hyperspectral imaging (HSI) is a noninvasive technique for transcutaneous measurements of tissue perfusion. This study (1) provides a review of the current literature on HSI for tissue perfusion measurements of the lower leg and (2) introduces a standardized measurement protocol for HSI measurements with a portable system. EVIDENCE ACQUISITION: A literature search was performed for studies on tissue perfusion measurements with HSI in the lower extremity. A standardized protocol was developed to perform HSI measurements in 43 healthy volunteers at the plantar side of the foot and at the lateral side of the calf, with 3 consecutive hyperspectral images at each location. EVIDENCE SYNTHESIS: The literature review identified 9 studies, including 2 of healthy volunteers, 4 of patients with diabetes mellitus, and 3 of patients with peripheral arterial disease. In 5 of 7 patient studies, HSI values were associated with severity of disease or wound healing. In our study, the healthy volunteers' HSI values for oxyhemoglobin, deoxyhemoglobin, and oxygen saturation were (mean±SD) 82.8±24, 55.7±15.7, and 59.2±11.7, respectively, at the plantar surface of the foot, and 40.8±11, 38.0±7.8, and 51.7±10.5, respectively, at the lateral side of the calf. HSI values differed significantly between the calf and plantar locations. Intraoperator reliability between the 3 consecutive images ranged from 81% to 89%. CONCLUSIONS: Limited evidence indicates that HSI is associated with severity of peripheral arterial disease and diabetes mellitus, and with wound healing. Hyperspectral images with a portable system can be taken with high precision when a standardized measurement protocol is used. However, differences exist at several locations at the lower extremity, so each measurement location should be used as its own reference when consecutive measurements are performed during follow-up. More studies with larger patient cohorts should be performed before HSI can be incorporated as standard tool in the diagnostic armamentarium of the vascular specialist.

Two decades of SPECT/CT - the coming of age of a technology: An updated review of literature evidence.

PURPOSE: Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) was introduced as a hybrid SPECT/CT imaging modality two decades ago. The main advantage of SPECT/CT is the increased specificity achieved through a more precise localization and characterization of functional findings. The improved diagnostic accuracy is also associated with greater diagnostic confidence and better inter-specialty communication. METHODS: This review presents a critical assessment of the relevant literature published so far on the role of SPECT/CT in a variety of clinical conditions. It also includes an update on the established evidence demonstrating both the advantages and limitations of this modality. CONCLUSIONS: For the majority of applications, SPECT/CT should be a routine imaging technique, fully integrated into the clinical decision-making process, including oncology, endocrinology, orthopaedics, paediatrics, and cardiology. Large-scale prospective studies are lacking, however, on the use of SPECT/CT in certain clinical domains such as neurology and lung disorders. The review also presents data on the complementary role of SPECT/CT with other imaging modalities and a comparative analysis, where available.

Independent and incremental value of ventilation/perfusion PET/CT and CT pulmonary angiography for pulmonary embolism diagnosis: results of the PECAN pilot study.

PURPOSE: This pilot study assessed the independent and incremental value of 68Ga-V/Q PET/CT as compared with CT pulmonary angiography (CTPA) for the management of cancer patients with suspected acute pulmonary embolism (PE). METHODS: All 24 cancer patients with suspected acute PE prospectively recruited underwent both 68Ga-V/Q PET/CT and CTPA within 24 h. PET/CT was acquired after inhalation of Galligas prepared using a Technegas generator and administration of 68Ga-macroaggregated albumin. Initially, PET/CT and CTPA scans were read independently with the reader blinded to the results of the other imaging study. CTPA and PET/CT were then coregistered and reviewed by consensus between a radiologist and nuclear medicine physician. The therapeutic management was established by the managing physician based on all available data. RESULTS: The diagnostic conclusion was concordantly negative in 18 patients (75%). Of the six discordant diagnoses on independent reading, combined interpretation of V/Q PET/CTPA enabled a consensus conclusion in two patients, excluding PE in one and confirming PE in the other, similar to the initial diagnostic conclusion of the V/Q PET/CT. Of the remaining four patients, three had a single subsegmental thrombus on CTPA but a negative V/Q PET/CT scan, and two of these did not receive long-term anticoagulation and did not have a venous thromboembolic event during a 3-year follow-up period. The third patient, along with a patient with a positive V/Q PET/CT scan but a negative CTPA scan, presented with acute complications preventing any conclusions with regard to the appropriateness of the V/Q PET/CT results in the management of PE. Overall, V/Q PET had an impact on management in four patients (17%). CONCLUSION: In this pilot study, we demonstrated the feasibility and potential utility of V/Q PET/CT for the management of patients with suspected PE. V/Q PET/CT may be of particular relevance in patients with equivocal findings or isolated subsegmental findings on CTPA, adding further discriminatory information to allow important decision-making regarding the use or withholding of anticoagulation. Given the other advantages of V/Q PET/CT (reduced acquisition time, low radiation dose), and with the increasing availability of 68Ga generators, PET/CT is a potential replacement for V/Q SPECT/CT imaging.

Achieving comparable perfusion results across vendors. The next step in standardizing stroke care: a technical report.

BACKGROUND: The role of mechanical thrombectomy in acute ischemic stroke (AIS) has been further expanded by recent trials which relied on the results of CT perfusion (CTP) imaging. However, CTP parameters for ischemia and infarct can vary significantly across different vendors. METHODS: We compared the outcomes of the Siemens CTP software against the clinically validated RAPID software in 45 consecutive patients with suspected AIS. Both perfusion softwares initially processed images using vendor defined parameters for hypoperfusion and non-viable tissue. The software thresholds on the Siemens software were decrementally altered to see if concordant results between softwares could be attained. RESULTS: At baseline settings, the mean values for core infarct and hypoperfusion were different (mean of 30/69 mL, respectively, for RAPID and 49/77 mL for Siemens). However, reducing the threshold values for the later software showed a concordance of values at a relative cerebral blood flow <20%, with resulting core infarct and hypoperfusion volumes at 31/69 mL, respectively, for the Siemens software. A Wilcoxon paired test showed no significant difference between the calculated core infarct and hypoperfusion values, both for the entire population as well as for the subgroup of patients with large vessel occlusion. CONCLUSION: Equivalent CTP results between vendor softwares may be attainable by altering the thresholds for hypoperfused and non-viable tissue, despite differences in acquisition techniques, post-processing, and scanners.

Advanced MR imaging and 18F-DOPA PET characteristics of H3K27M-mutant and wild-type pediatric diffuse midline gliomas.

PURPOSE: The aim of this study was to investigate MRI-derived diffusion weighted imaging (DWI), 1H-MR spectroscopy (1H-MRS) and arterial spin labeling (ASL) perfusion imaging in comparison with 18F-dihydroxyphenylalanine (DOPA) PET with respect to diagnostic evaluation of pediatric diffuse midline gliomas (DMG) H3K27M-mutant and wild-type. METHODS: We retrospectively analyzed 22 pediatric patients with DMG histologically proved and molecularly classified as H3K27M-mutant (12 subjects) and wild-type (10 subjects) who underwent DWI, 1H-MRS, and ASL performed within 2 weeks of 18F-DOPA PET. DWI-derived relative minimum apparent diffusion coefficient (rADC min), 1H-MRS data [choline/N-acetylaspartate (Cho/NAA), choline/creatine (Cho/Cr), and presence of lactate] and relative ASL-derived cerebral blood flow max (rCBF max) were compared with 18F-DOPA uptake Tumor/Normal tissue (T/N) and Tumor/Striatum (T/S) ratios, and correlated with histological and molecular features of DMG. Statistics included Pearson's chi-square and Mann-Whitney U tests, Spearman's rank correlation and receiver operating characteristic (ROC) analysis. RESULTS: The highest degrees of correlation among different techniques were found between T/S, rADC min and Cho/NAA ratio (p < 0.01), and between rCBF max and rADC min (p < 0.01). Significant differences between histologically classified low- and high-grade DMG, independently of H3K27M-mutation, were found among all imaging techniques (p ≤ 0.02). Significant differences in terms of rCBF max, rADC min, Cho/NAA and 18F-DOPA uptake were also found between molecularly classified mutant and wild-type DMG (p ≤ 0.02), even though wild-type DMG included low-grade astrocytomas, not present among mutant DMG. When comparing only histologically defined high-grade mutant and wild-type DMG, only the 18F-DOPA PET data T/S demonstrated statistically significant differences independently of histology (p < 0.003). ROC analysis demonstrated that T/S ratio was the best parameter for differentiating mutant from wild-type DMG (AUC 0.94, p < 0.001). CONCLUSIONS: Advanced MRI and 18F-DOPA PET characteristics of DMG depend on histological features; however, 18F-DOPA PET-T/S was the only parameter able to discriminate H3K27M-mutant from wild-type DMG independently of histology.

Referring Physicians Assess the Quality of Outpatient Diagnostic Imaging Services: Development and Psychometric Evaluation of a Questionnaire.

GOAL: In order to ensure high-quality cooperation between referring physicians and imaging services, it is important to assess the quality of imaging services as perceived by referring physicians. The present study aimed to develop and validate a questionnaire for referring physicians to assess the quality of outpatient diagnostic imaging services. MATERIALS & METHODS: The questionnaire was developed by discussing and modifying an existing instrument by the German Association of Surgeons. After qualitative pretesting, the instrument was tested with physicians referring to four outpatient diagnostic imaging services in Switzerland. The results were first assessed using descriptive statistics. The final instrument was tested for validity using the concept of known-groups validity. The hypothesis underlying this procedure was that physicians referring frequently to services estimated the quality of these services to be higher than physicians who referred less often to services. The differences in ratings were assessed using a one-sided two-sample Wilcoxon test. The final questionnaire was tested for internal consistency and reliability using Cronbach's Alpha. RESULTS: Results show a high level of satisfaction of referring physicians with the relevant services but also potential for quality improvement initiatives. The psychometric evaluation of the final questionnaire shows that it is a valid instrument, showing significant differences between the ratings of physicians referring with high and low frequency. Furthermore, the instrument proves to be consistent and reliable. CONCLUSION: The final instrument presents a valid, consistent and reliable option for assess the quality of outpatient diagnostic imaging services as perceived by referring physicians. Results can be used as a basis for quality improvement. KEY POINTS: · A newly developed questionnaire assesses the quality of outpatient diagnostic imaging services as perceived by referring physicians. The questionnaire was developed and tested in Switzerland.. · Psychometric evaluation showed the questionnaire to be a valid, consistent and reliable instrument.. · Results are of interest for imaging services as well as for initiatives encompassing several services.. CITATION FORMAT: · Jossen M, Valeri F, Heilmaier C et al. Referring Physicians Assess the Quality of Outpatient Diagnostic Imaging Services: Development and Psychometric Evaluation of a Questionnaire. Fortschr Röntgenstr 2019; 191: 725 - 731.

Noninvasive imaging of hepatocellular carcinoma: From diagnosis to prognosis.

Hepatocellular carcinoma (HCC) is the most common primary liver cancer and a major public health problem worldwide. Hepatocarcinogenesis is a complex multistep process at molecular, cellular, and histologic levels with key alterations that can be revealed by noninvasive imaging modalities. Therefore, imaging techniques play pivotal roles in the detection, characterization, staging, surveillance, and prognosis evaluation of HCC. Currently, ultrasound is the first-line imaging modality for screening and surveillance purposes. While based on conclusive enhancement patterns comprising arterial phase hyperenhancement and portal venous and/or delayed phase wash-out, contrast enhanced dynamic computed tomography and magnetic resonance imaging (MRI) are the diagnostic tools for HCC without requirements for histopathologic confirmation. Functional MRI techniques, including diffusion-weighted imaging, MRI with hepatobiliary contrast agents, perfusion imaging, and magnetic resonance elastography, show promise in providing further important information regarding tumor biological behaviors. In addition, evaluation of tumor imaging characteristics, including nodule size, margin, number, vascular invasion, and growth patterns, allows preoperative prediction of tumor microvascular invasion and patient prognosis. Therefore, the aim of this article is to review the current state-of-the-art and recent advances in the comprehensive noninvasive imaging evaluation of HCC. We also provide the basic key concepts of HCC development and an overview of the current practice guidelines.

Can diffusion- and perfusion-weighted imaging alone accurately triage anterior circulation acute ischemic stroke patients to endovascular therapy?

BACKGROUND AND PURPOSE: Acute ischemic stroke (AIS) patients who benefit from endovascular treatment have a large vessel occlusion (LVO), small core infarction, and salvageable brain. We determined if diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) alone can correctly identify and localize anterior circulation LVO and accurately triage patients to endovascular thrombectomy (ET). MATERIALS AND METHODS: This retrospective cohort study included patients undergoing MRI for the evaluation of AIS symptoms. DWI and PWI images alone were anonymized and scored for cerebral infarction, LVO presence and LVO location, DWI-PWI mismatch, and ET candidacy. Readers were blinded to clinical data. The primary outcome measure was accurate ET triage. Secondary outcomes were detection of LVO and LVO location. RESULTS: Two hundred and nineteen patients were included. Seventy-three patients (33%) underwent endovascular AIS treatment. Readers correctly and concordantly triaged 70 of 73 patients (96%) to ET (κ=0.938; P=0.855) and correctly excluded 143 of 146 patients (98%; P=0.942). DWI and PWI alone had a 95.9% sensitivity and a 98.4% specificity for accurate endovascular triage. LVO were accurately localized to the ICA/M1 segment in 65 of 68 patients (96%; κ=0.922; P=0.817) and the M2 segment in 18 of 20 patients (90%; κ=0.830; P=0.529). CONCLUSION: AIS patients with anterior circulation LVO are accurately identified using DWI and PWI alone, and LVO location may be correctly inferred from PWI. MRA omission may be considered to expedite AIS triage in hyperacute scenarios or may confidently supplant non-diagnostic or artifact-limited MRA.

Which is the optimal threshold for defining functional lung in single-photon emission computed tomography lung perfusion imaging of lung cancer patients?

PURPOSE: The aim of this study was to investigate the optimal threshold for the functional lung (FL) definition of single-photon emission computed tomography (SPECT) lung perfusion imaging. PATIENTS AND METHODS: Forty consecutive stage III non-small-cell lung cancer patients underwent SPECT lung perfusion scans and PET/CT scans for treatment planning, and the images were coregistered. Total lung and perfusion lung volumes corresponding to 10, 20, …, 60% of the maximum SPECT count were segmented automatically. The SPECT-weighted mean lung dose (SWMDx%) and the percentage of FL volume receiving more than 20 Gy (Fx%V20) of different thresholds were investigated using SPECT-weighted dose-volume histograms. Receiver-operator characteristic curves were used to identify SWMD and FV20 of different thresholds in predicting the incidence of radiation pneumonitis (RP). RESULTS: Eleven (27.5%) patients developed RP (grades 1, 2, 3, and 4 were 10.0, 7.5, 7.5, and 2.5%, respectively) after treatment. The largest area under the receiver-operator characteristic curve was 0.881 for the ability of SWMD to predict RP with 20% as the threshold and 0.928 for the ability of FV20 with 20% as the threshold. CONCLUSION: The SWMD20% and FV20 of FL using 20% of the maximum SPECT count as the threshold may be better predictors for the risk of RP.

Quantification of tumor perfusion using dynamic contrast-enhanced ultrasound: impact of mathematical modeling.

Dynamic contrast-enhanced ultrasound has been proposed to monitor tumor therapy, as a complement to volume measurements. To assess the variability of perfusion parameters in ideal conditions, four consecutive test-retest studies were acquired in a mouse tumor model, using controlled injections. The impact of mathematical modeling on parameter variability was then investigated. Coefficients of variation (CV) of tissue blood volume (BV) and tissue blood flow (BF) based-parameters were estimated inside 32 sub-regions of the tumors, comparing the log-normal (LN) model with a one-compartment model fed by an arterial input function (AIF) and improved by the introduction of a time delay parameter. Relative perfusion parameters were also estimated by normalization of the LN parameters and normalization of the one-compartment parameters estimated with the AIF, using a reference tissue (RT) region. A direct estimation (rRTd) of relative parameters, based on the one-compartment model without using the AIF, was also obtained by using the kinetics inside the RT region. Results of test-retest studies show that absolute regional parameters have high CV, whatever the approach, with median values of about 30% for BV, and 40% for BF. The positive impact of normalization was established, showing a coherent estimation of relative parameters, with reduced CV (about 20% for BV and 30% for BF using the rRTd approach). These values were significantly lower (p < 0.05) than the CV of absolute parameters. The rRTd approach provided the smallest CV and should be preferred for estimating relative perfusion parameters.

Improved hepatic arterial fraction estimation using cardiac output correction of arterial input functions for liver DCE MRI.

Liver dynamic contrast enhanced (DCE) MRI pharmacokinetic modelling could be useful in the assessment of diffuse liver disease and focal liver lesions, but is compromised by errors in arterial input function (AIF) sampling. In this study, we apply cardiac output correction to arterial input functions (AIFs) for liver DCE MRI and investigate the effect on dual-input single compartment hepatic perfusion parameter estimation and reproducibility. Thirteen healthy volunteers (28.7 ± 1.94 years, seven males) underwent liver DCE MRI and cardiac output measurement using aortic root phase contrast MRI (PCMRI), with reproducibility (n = 9) measured at 7 d. Cardiac output AIF correction was undertaken by constraining the first pass AIF enhancement curve using the indicator-dilution principle. Hepatic perfusion parameters with and without cardiac output AIF correction were compared and 7 d reproducibility assessed. Differences between cardiac output corrected and uncorrected liver DCE MRI portal venous (PV) perfusion (p = 0.066), total liver blood flow (TLBF) (p = 0.101), hepatic arterial (HA) fraction (p = 0.895), mean transit time (MTT) (p = 0.646), distribution volume (DV) (p = 0.890) were not significantly different. Seven day corrected HA fraction reproducibility was improved (mean difference 0.3%, Bland-Altman 95% limits-of-agreement (BA95%LoA) ±27.9%, coefficient of variation (CoV) 61.4% versus 9.3%, ±35.5%, 81.7% respectively without correction). Seven day uncorrected PV perfusion was also improved (mean difference 9.3 ml min-1/100 g, BA95%LoA ±506.1 ml min-1/100 g, CoV 64.1% versus 0.9 ml min-1/100 g, ±562.8 ml min-1/100 g, 65.1% respectively with correction) as was uncorrected TLBF (mean difference 43.8 ml min-1/100 g, BA95%LoA ±586.7 ml min-1/ 100 g, CoV 58.3% versus 13.3 ml min-1/100 g, ±661.5 ml min-1/100 g, 60.9% respectively with correction). Reproducibility of uncorrected MTT was similar (uncorrected mean difference 2.4 s, BA95%LoA ±26.7 s, CoV 60.8% uncorrected versus 3.7 s, ±27.8 s, 62.0% respectively with correction), as was and DV (uncorrected mean difference 14.1%, BA95%LoA ±48.2%, CoV 24.7% versus 10.3%, ±46.0%, 23.9% respectively with correction). Cardiac output AIF correction does not significantly affect the estimation of hepatic perfusion parameters but demonstrates improvements in normal volunteer 7 d HA fraction reproducibility, but deterioration in PV perfusion and TLBF reproducibility. Improved HA fraction reproducibility maybe important as arterialisation of liver perfusion is increased in chronic liver disease and within malignant liver lesions.

Invited review--neuroimaging response assessment criteria for brain tumors in veterinary patients.

The evaluation of therapeutic response using cross-sectional imaging techniques, particularly gadolinium-enhanced MRI, is an integral part of the clinical management of brain tumors in veterinary patients. Spontaneous canine brain tumors are increasingly recognized and utilized as a translational model for the study of human brain tumors. However, no standardized neuroimaging response assessment criteria have been formulated for use in veterinary clinical trials. Previous studies have found that the pathophysiologic features inherent to brain tumors and the surrounding brain complicate the use of the response evaluation criteria in solid tumors (RECIST) assessment system. Objectives of this review are to describe strengths and limitations of published imaging-based brain tumor response criteria and propose a system for use in veterinary patients. The widely used human Macdonald and response assessment in neuro-oncology (RANO) criteria are reviewed and described as to how they can be applied to veterinary brain tumors. Discussion points will include current challenges associated with the interpretation of brain tumor therapeutic responses such as imaging pseudophenomena and treatment-induced necrosis, and how advancements in perfusion imaging, positron emission tomography, and magnetic resonance spectroscopy have shown promise in differentiating tumor progression from therapy-induced changes. Finally, although objective endpoints such as MR imaging and survival estimates will likely continue to comprise the foundations for outcome measures in veterinary brain tumor clinical trials, we propose that in order to provide a more relevant therapeutic response metric for veterinary patients, composite response systems should be formulated and validated that combine imaging and clinical assessment criteria.