Ryotaro Kamei

Multiparametric voxel-based analyses of standardized uptake values and apparent diffusion coefficients of soft-tissue tumours with a positron emission tomography/magnetic resonance system: Preliminary results

AbstractObjectivesTo investigate the usefulness of voxel-based analysis of standardized uptake values (SUVs) and apparent diffusion coefficients (ADCs) for evaluating soft-tissue tumour malignancy with a PET/MR system.MethodsThirty-five subjects with either ten low/intermediate-grade tumours or 25 high-grade tumours were prospectively enrolled. Zoomed diffusion-weighted and fluorodeoxyglucose (18FDG)-PET images were acquired along with fat-suppressed T2-weighted images (FST2WIs). Regions of interest (ROIs) were drawn on FST2WIs including the tumour in all slices. ROIs were pasted onto PET and ADC-maps to measure SUVs and ADCs within tumour ROIs. Tumour volume, SUVmax, ADCminimum, the heterogeneity and the correlation coefficients of SUV and ADC were recorded. The parameters of high- and low/intermediate-grade groups were compared, and receiver operating characteristic (ROC) analysis was also performed.ResultsThe mean correlation coefficient for SUV and ADC in high-grade sarcomas was lower than that of low/intermediate-grade tumours (−0.41 ± 0.25 vs. −0.08 ± 0.34, P < 0.01). Other parameters did not differ significantly. ROC analysis demonstrated that correlation coefficient showed the best diagnostic performance for differentiating the two groups (AUC 0.79, sensitivity 96.0%, specificity 60%, accuracy 85.7%).ConclusionsSUV and ADC determined via PET/MR may be useful for differentiating between high-grade and low/intermediate-grade soft tissue tumours.Key Points• PET/MR allows voxel-based comparison of SUVs and ADCs in soft-tissue tumours. • A comprehensive assessment of internal heterogeneity was performed with scatter plots. • SUVmax or ADCminimum could not differentiate high-grade sarcoma from low/intermediate-grade tumours. • Only the correlation coefficient between SUV and ADC differentiated the two groups. • The correlation coefficient showed the best diagnostic performance by ROC analysis.

Diffusivity of intraorbital lymphoma vs. inflammation: comparison of single shot turbo spin echo and multishot echo planar imaging techniques

AbstractPurposeTo compare the abilities of turbo spin-echo diffusion-weighted imaging (TSE DWI) and multi-shot echo planar DWI (MSh DWI) to discriminate orbital lymphoma from inflammatory lesions.Materials and methodsTwenty-nine patients with pathologically confirmed lymphomas and 39 patients with inflammation were imaged with a 3.0-T system. The apparent diffusion coefficient (ADC) of each lesion was measured. Signal intensities compared to normal grey matter on conventional imaging were also measured.ResultsThe ADCs derived from the TSE DWI of the lymphomas (0.68 ± 0.14 × 10−3 mm2/s) were significantly lower than those of the inflammation cases (1.04 ± 0.39 × 10−3 mm2/s; p < 0.001). The ADCs derived from MSh DWI could not be used to separate the lymphomas from the inflammation (1.16 ± 0.43 × 10−3 mm2/s vs. 1.36 ± 0.48 × 10−3 mm2/s; p = 0.06). Conventional sequences also could not separate the lymphomas from the inflammation (p > 0.05). The ROC analysis showed the best diagnostic performance with ADCs derived from TSE DWI (the area under the curve: AUC = 0.831) followed by ADC derived from MSh DWI (AUC = 0.633).ConclusionThe ADCs derived from TSE DWI might help to differentiate orbital lymphomas from inflammation.Key Points• ADC of lymphoma was significantly lower than that of inflammation. • ADC derived from TSE DWI showed the best diagnostic performance. • This study was conducted by a 3-T MR scanner.

Acceleration-selective Arterial Spin-labeling MR Angiography Used to Visualize Distal Cerebral Arteries and Collateral Vessels in Moyamoya Disease

Purpose To evaluate and compare the performance of acceleration-selective arterial spin labeling (AccASL) magnetic resonance (MR) angiography in the visualization of cerebral arteries and collateral vessels in patients with Moyamoya disease with that of time-of-flight (TOF) MR angiography, with digital subtraction angiography (DSA) as the reference standard. Materials and Methods Thirty-six cerebral hemispheres from 22 patients with Moyamoya disease underwent TOF and AccASL MR angiography and DSA. Qualitative evaluations included imaging of the terminal internal carotid artery (ICA), distal middle cerebral arteries (MCAs), Moyamoya vessels, and leptomeningeal anastomosis (LMA) collaterals with reference to DSA. Quantitative evaluations included assessment of contrast-to-noise ratio (CNR) and number of vessels in MCA branches. The linear mixed-effect model was used to compare the two methods. Results Mean scores for qualitative evaluation were significantly higher with AccASL angiography than with TOF angiography for imaging distal MCAs (3.9 ± 0.3 [standard deviation] vs 2.9 ± 1.1; P < .001), Moyamoya vessels (3.6 ± 0.6 vs 2.7 ± 0.9, P < .001), and LMA collaterals (3.8 ± 0.6 vs 1.8 ± 0.7, P < .001). Scores for steno-occlusive degree around the terminal ICAs were better with TOF angiography than with AccASL angiography (2.6 ± 0.5 vs 2.4 ± 0.6, P = .023). CNRs in the M4 segment were significantly higher with AccASL angiography (11.9 ± 12.9, P < .001) than with TOF angiography (4.1 ± 7.9). The number of vessels was significantly higher with AccASL angiography (18.3 ± 5.0, P < .001) than with TOF angiography (8.9 ± 4.9). The increase in the number of vessels from TOF angiography to AccASL angiography was greater in patients with severe ICA steno-occlusion (late ICA stage group, 11.4 ± 4.5; early ICA stage group, 6.8 ± 4.0; P = .007) and well-developed leptomeningeal anastomosis (mildly developed LMA group, 7.1 ± 4.3; well-developed LMA group, 11.3 ± 4.5; P = .011). Conclusion AccASL MR angiography enables better visualization of distal cerebral arteries and collateral vessels in patients with Moyamoya disease than does TOF MR angiography, while TOF MR angiography enables better visualization of stenosis of proximal arteries. Both methods work in a mutually beneficial manner in the assessment of cerebral arteries.

Cerebral blood flow laterality derived from arterial spin labeling as a biomarker for assessing the disease severity of parkinson's disease

To evaluate cerebral blood flow (CBF) laterality derived from arterial spin labeling (ASL) in early‐stage Parkinsons disease (PD) patients compared with those with advanced stages.

Comparison of positron emission tomography diffusion‐weighted imaging (PET/DWI) registration quality in a PET/MR scanner: Zoomed DWI vs. Conventional DWI

To compare zoomed diffusion‐weighted imaging (z‐DWI) with reduced field of view (FOV) by spatially selective radiofrequency pulses and conventional echo planar imaging (EPI) DWI (c‐DWI) with regard to registration quality using positron emission tomography / magnetic resonance (PET/MR) in patients with malignant tumors.

An improved MR sequence for attenuation correction in PET/MR hybrid imaging.

The aim of this study was to investigate the effects of MR parameters on tissue segmentation and determine the optimal MR sequence for attenuation correction in PET/MR hybrid imaging. Eight healthy volunteers were examined using a PET/MR hybrid scanner with six three-dimensional turbo-field-echo sequences for attenuation correction by modifying the echo time, k-space trajectory in the phase-encoding direction, and image contrast. MR images for attenuation correction were obtained from six MR sequences in each session; each volunteer underwent four sessions. Two radiologists assessed the attenuation correction maps generated from the MR images with respect to segmentation errors and ghost artifacts on a five-point scale, and the scores were decided by consensus. Segmentation accuracy and reproducibility were compared. Multiple regression analysis was performed to determine the effects of each MR parameter. The two three-dimensional turbo-field-echo sequences with an in-phase echo time and radial k-space sampling showed the highest total scores for segmentation accuracy, with a high reproducibility. In multiple regression analysis, the score with the shortest echo time (-3.44, P<0.0001) and Cartesian sampling in the anterior/posterior phase-encoding direction (-2.72, P=0.002) was significantly lower than that with in-phase echo time and Cartesian sampling in the right/left phase-encoding direction. Radial k-space sampling provided a significantly higher score (+5.08, P<0.0001) compared with Cartesian sampling. Furthermore, radial sampling improved intrasubject variations in the segmentation score (-8.28%, P=0.002). Image contrast had no significant effect on the total score or reproducibility. These results suggest that three-dimensional turbo-field-echo MR sequences with an in-phase echo time and radial k-space sampling provide improved MR-based attenuation correction maps.

Arterial spin-labeling is useful for the diagnosis of residual or recurrent meningiomas

ObjectivesASL is useful in evaluating tumour blood flow and in detecting hypervascular tumours. The purpose of this study was to assess the additive value of ASL to non-contrast and contrast-enhanced (NC/CE)-T1WI for diagnosing residual or recurrent meningiomas.MethodsThis retrospective study included 25 postoperative patients (20 women, 5 men; median age, 65 [32–85] years) with and 25 gender- and age-matched postoperative patients without residual or recurrent meningiomas. ASL was performed using a pseudocontinuous method. Seven independent observers (two radiology residents, two general radiologists and three neuroradiologists) participated in two reading sessions consisting of only NC/CE-T1WI (first session) or NC/CE-T1WI with ASL (second session). We evaluated the sensitivity and diagnostic performance for the detection of residual or recurrent meningiomas. The diagnostic performance was assessed using a figure of merit (FOM) calculated via jackknife free-response receiver-operating characteristics. Statistical analysis was performed with paired t tests, with a significance level of p < .05.ResultsThe sensitivities were as follows (NC/CE-T1WI vs. NC/CE-T1WI with ASL): residents (62.1% vs. 70.7%), general radiologists (75.9% vs. 87.9%), neuroradiologists (97.7% vs. 100%) and all observers (81.3% vs. 88.2%). The FOMs were as follows (NC/CE-T1WI vs. NC/CE-T1WI with ASL): residents (0.76 vs. 0.83), general radiologists (0.83 vs. 0.93), neuroradiologists (0.95 vs. 0.99) and all observers (0.86 vs. 0.93). The addition of ASL significantly improved the diagnostic parameters for all observers except neuroradiologists (p <. 05).ConclusionsASL improved the detection rate of residual or recurrent meningiomas on NC/CE-T1WI among both radiology residents and general radiologists.Key Points• ASL improved diagnostic performance for residual/recurrent meningioma compare to NC/CE-T1WI alone.• Diagnostic sensitivity was increased after adding ASL compared with NC/CE-T1WI.• FOM was increased after adding ASL compared with NC/CE-T1WI.

Optimal monochromatic color combinations for fusion imaging of FDG-PET and diffusion-weighted MR images

ObjectiveTo investigate the optimal monochromatic color combination for fusion imaging of FDG-PET and diffusion-weighted MR images (DW) regarding lesion conspicuity of each image.MethodsSix linear monochromatic color-maps of red, blue, green, cyan, magenta, and yellow were assigned to each of the FDG-PET and DW images. Total perceptual color differences of the lesions were calculated based on the lightness and chromaticity measured with the photometer. Visual lesion conspicuity was also compared among the PET-only, DW-only and PET-DW-double positive portions with mean conspicuity scores. Statistical analysis was performed with a one-way analysis of variance and Spearman’s rank correlation coefficient.ResultsAmong all the 12 possible monochromatic color-map combinations, the 3 combinations of red/cyan, magenta/green, and red/green produced the highest conspicuity scores. Total color differences between PET-positive and double-positive portions correlated with conspicuity scores (ρ = 0.2933, p < 0.005). Lightness differences showed a significant negative correlation with conspicuity scores between the PET-only and DWI-only positive portions. Chromaticity differences showed a marginally significant correlation with conspicuity scores between DWI-positive and double-positive portions.ConclusionsMonochromatic color combinations can facilitate the visual evaluation of FDG-uptake and diffusivity as well as registration accuracy on the FDG-PET/DW fusion images, when red- and green-colored elements are assigned to FDG-PET and DW images, respectively.