Interscan Variability Research Articles

P5280The impact of background phase offset errors in cardiovascular magnetic resonance phase contrast imaging: a multi-scanner study

Abstract Background Phase contrast (PC) CMR flow measurements (FM) are widely used for blood flow assessment, but they suffer from phase offset errors (POE). Stationary phantom correction limits these inaccuracies, however, this adds scan time. Stationary tissue (ST) correction is an alternative method that does not require additional scanning. The aim of this study was to evaluate the impact of POE, to assess interscanner variation, and to evaluate the ST correction usage. Methods We included 166 patients in which both aorta and main pulmonary artery FM were acquired including static gelatin phantom data. Subjects were scanned on three types of 1.5T scanners from the one vendor. Uncorrected and ST corrected FM were compared with phantom corrected FM, our reference value, and corrected for BSA. A difference of >10% in net flow was defined as clinically relevant. Regurgitation fraction was calculated and POE influences were assessed. Regurgitation severity was graded and POE influence on severity grading was assessed. Results Of the 166 cases included, the median age was 27 (5–74) years. Overall, the median difference between no corrected and phantom corrected FM was ≤6%, however, with a wide range of over- and underestimation (−155%–78% change) (figure). ST correction resulted in larger differences compared to no correction (p<0.01). Clinically significant differences were seen in 19% of all FM with no correction and in 30% of with ST correction (p<0.01). Furthermore, there were significant differences between scanners (no correction 10%, p<0.01; ST correction, p<0.01). Regurgitation severity indexing changed in 38 (11%) cases with no correction and in 48 (48%) with ST correction. Magnitude of flow change with and without offset corrections (n=332) Flow (ml/m2) Δ no correction and phantom correction (%) Δ ST correction and phantom correction (%) Clinically significant difference (>10%) Mean ± SD Median IQR Range Median IQR Range No correction, N (%) ST correction , N (%) MRI 1 (n=126) 50±12 3 0 to 6 −8 to 30 5 −3 to 9 −26 to 28 13 (10%) 34 (27%) MRI 2 (n=102) 48±13 −2 −15 to 6 −155 to 78 5 −3 to 11 −74 to 52 50 (49%) 50 (49%) MRI 3 (n=104) 48±12 −1 −1 to 0 −7 to 14 2 −2 to 5 −39 to 29 1 (1%) 16 (15%) Total (n=332) 49±12 0 −2 to 4 −155 to 78 3 −2 to 8 −74 to 52 64 (19%) 100 (30%) Conclusion Background POE have a significant impact on flow quantification and regurgitation severity. Unexpectedly, background correction using ST correction worsens accuracy compared to no correction. POE vary greatly between scanners. Therefore, careful assessment of FM at each scanner is essential to determine if routine phantom scanning is necessary.

Effects of alterations in positron emission tomography imaging parameters on radiomics features.

Radiomics studies require large patient cohorts, which often include patients imaged using different imaging protocols. We aimed to determine the impact of variability in imaging protocol parameters and interscanner variability using a phantom that produced feature values similar to those of patients. Positron emission tomography (PET) scans of a Hoffman brain phantom were acquired on GE Discovery 710, Siemens mCT, and Philips Vereos scanners. A standard-protocol scan was acquired on each machine, and then each parameter that could be changed was altered individually. The phantom was contoured with 10 regions of interest (ROIs). Values for 45 features with 2 different preprocessing techniques were extracted for each image. To determine the impact of each parameter on the reliability of each radiomics feature, the intraclass correlation coefficient (ICC) was calculated with the ROIs as the subjects and the parameter values as the raters. For interscanner comparisons, we compared the standard deviation of each radiomics feature value from the standard-protocol images to the standard deviation of the same radiomics feature from PET scans of 224 patients with non-small cell lung cancer. When the pixel size was resampled prior to feature extraction, all features had good reliability (ICC > 0.75) for the field of view and matrix size. The time per bed position had excellent reliability (ICC > 0.9) on all features. When the filter cutoff was restricted to values below 6 mm, all features had good reliability. Similarly, when subsets and iterations were restricted to reasonable values used in clinics, almost all features had good reliability. The average ratio of the standard deviation of features on the phantom scans to that of the NSCLC patient scans was 0.73 using fixed-bin-width preprocessing and 0.92 using 64-level preprocessing. Most radiomics feature values had at least good reliability when imaging protocol parameters were within clinically used ranges. However, interscanner variability was about equal to interpatient variability; therefore, caution must be used when combining patients scanned on equipment from different vendors in radiomics data sets.

Coronal Flexion Versus Coronal Neutral Sonographic Views in Infantile DDH: An Important Source of Variability.

Ultrasound (US) is the preferred imaging modality for the diagnosis and treatment of infantile developmental dysplasia of the hip (DDH). Currently accepted indices that distinguish normal from dysplastic hips in the coronal plane include percent femoral head coverage (FHC), α angle, and β angle. Recent data suggests that significant user and interscan variability may exist for these metrics. Less studied, however, is potential variability because of patient positioning, specifically coronal flexion versus coronal neutral views. The purpose of this study was to compare standard DDH indices between coronal US views with hips in flexion versus neutral positions, for hips of varying DDH severity. This retrospective study included normal infants and those treated for different severities of DDH. Coronal flexion and coronal neutral US images from the same study were evaluated at diagnosis, early treatment, start of weaning, and treatment resolution. FHC, α, and β angles were measured on both views at each time point and compared. Inter-rater and intra-rater reliability assessments were performed for all metrics. Among the 168 hips in this study (45 normals, 45 Ortolani positive, 17 Barlow positive, and 61 stable dysplasia), median FHC was significantly lower in coronal flexion compared with coronal neutral for normals and all 3 severities of DDH at each time point (mean decrease 8.4%; range 5.5% to 10.9%; P<0.01). Alpha angle also decreased on coronal flexion views, observed for all hip types, but only at certain time points (mean decrease 3.3 degrees; range 0 to 7.5 degrees; P<0.01 to 0.35). β angles demonstrated less variability between views, but also had poor reliability. Coronal flexion and coronal neutral views demonstrated significant differences in FHC and α angle across a spectrum of DDH severities and treatment time points. Flexion views may represent a "baby Barlow" test, revealing subtle instability as evidenced by the significant and consistent decrease in FHC across all hips. Indices measured in flexion, therefore, may represent more stringent criteria for defining normal hips. Level III-diagnostic study.

Quality assurance measurements of geometric accuracy for magnetic resonance imaging-based radiotherapy treatment planning

BackgroundUsing magnetic resonance imaging (MRI) as the only imaging method for radiotherapy treatment planning (RTP) is becoming more common as MRI-only RTP solutions have evolved. The geometric accuracy of MR images is an essential factor of image quality when determining the suitability of MRI for RTP. The need is therefore clear for clinically feasible quality assurance (QA) methods for the geometric accuracy measurement. Materials and methodsThis work evaluates long-term stability of geometric accuracy and the validity of a 2D geometric accuracy QA method compared to a prototype 3D method and analysis software in routine QA. The long-term follow-up measurements were conducted on one of the 1.5 T scanners over a period of 19 months using both methods. Inter-scanner variability of geometric distortions was also evaluated in three 1.5 T and three 3 T MRI scanners from a single vendor by using the prototype 3D QA method. ResultsThe geometric accuracy of the magnetic resonance for radiotherapy (MR-RT) platform remained stable within 2 mm at distances of <250 mm from isocenter. All scanners achieved good geometric accuracy with mean geometric distortions of <1 mm at <150 mm and <2 mm at <250 mm from the isocenter. Both measurement methods provided relevant information about geometric distortions. ConclusionsGeometric distortions are often considered a limitation of MRI-only RTP. Results indicate that geometric accuracy of modern scanners remain within acceptable limits by default even after many years of clinical use based on the 3D QA evaluation.

Radiation Dose Reduction at Pediatric CT: Use of Low Tube Voltage and Iterative Reconstruction-Erratum.

Given the growing awareness of and concern for potential carcinogenic effects of exposure of children to ionizing radiation at CT, optimizing acquisition parameters is crucial to achieve diagnostically acceptable image quality at the lowest possible radiation dose. Among currently available dose reduction techniques, recent technical innovations have allowed the implementation of low tube voltage scans and iterative reconstruction (IR) techniques into daily clinical practice for pediatric CT. The benefits of lowering tube voltage include a considerable reduction in radiation dose and improved contrast on images, especially when an iodinated contrast medium is used. The increase in noise, which is attributed to decreased photon penetration, is a major drawback but is not as severe as that at adult CT because of the small body size of children. In addition, use of IR algorithms can suppress increased noise, yielding wider applicability for low tube voltage scans. However, a careful implementation strategy and methodologic approach are necessary to maximize the potential for dose reduction while preserving diagnostic image quality under each clinical condition. The potential pitfalls of and topics related to these techniques include (a) the effect of tube voltage on the surface radiation dose, (b) the effect of window settings, (c) accentuation of metallic artifacts, (d) deterioration of low contrast detectability at low-dose settings, (e) interscanner variation of x-ray spectra, and (f) a comparison with the use of a spectral shaping technique. Appropriate use of low tube voltage and IR techniques is helpful for radiation dose reduction in most applications of pediatric CT. Online DICOM image stacks are available for this article . ©RSNA, 2018.

4D flow imaging with 2D-selective excitation.

4D flow MRI permits to quantify non-invasively time-dependent velocity vector fields, but it demands long acquisition times. 2D-selective excitation allows to accelerate the acquisition by reducing the FOV in both phase encoding directions. In this study, we investigate 2D-selective excitation with reduced FOV imaging for fast 4D flow imaging while obtaining correct velocity quantification. Two different 2D-selective excitation pulses were designed using spiral k-space trajectories. Further, their isophase time point was analyzed using simulations that considered both stationary and moving spins. On this basis, the 2D-selective RF pulses were implemented into a 4D flow sequence. A flow phantom study and seven 4D flow in vivo measurements were performed to assess the accuracy of velocity quantification by comparing the proposed technique to non-selective and conventional 1D slab-selective excitation. The isophase time point for spiral 2D-selective RF pulses was found to be located at the end of excitation for both stationary and moving spins. Based on that, 2D-selective excitation with reduced FOV allowed us to successfully quantify velocities both in a flow phantom and in vivo. In a flow phantom, the velocity difference between the smaller reduced FOV and the reference scan was similar to the inter-scan variability of . In vivo, the differences in flow (P = 0.995) and flow volume (P = 0.469) between the larger reduced FOV and the reference scan were non-significant. By reducing the FOV by two-thirds, acquisition time was halved. A reduced field-of-excitation allows to limit the FOV and therefore shorten 4D flow acquisition times while preserving successful velocity quantification.

Selective inversion recovery quantitative magnetization transfer imaging: Toward a 3 T clinical application in multiple sclerosis

Background: Assessing the degree of myelin injury in patients with multiple sclerosis (MS) is challenging due to the lack of magnetic resonance imaging (MRI) methods specific to myelin quantity. By measuring distinct tissue parameters from a two-pool model of the magnetization transfer (MT) effect, quantitative magnetization transfer (qMT) may yield these indices. However, due to long scan times, qMT has not been translated clinically. Objectives: We aim to assess the clinical feasibility of a recently optimized selective inversion recovery (SIR) qMT and to test the hypothesis that SIR-qMT-derived metrics are informative of radiological and clinical disease-related changes in MS. Methods: A total of 18 MS patients and 9 age- and sex-matched healthy controls (HCs) underwent a 3.0 Tesla (3 T) brain MRI, including clinical scans and an optimized SIR-qMT protocol. Four subjects were re-scanned at a 2-week interval to determine inter-scan variability. Results: SIR-qMT measures differed between lesional and non-lesional tissue (p < 0.0001) and between normal-appearing white matter (NAWM) of patients with more advanced disability and normal white matter (WM) of HCs (p < 0.05). SIR-qMT measures were associated with lesion volumes, disease duration, and disability scores (p ⩽ 0.002). Conclusion: SIR-qMT at 3 T is clinically feasible and predicts both radiological and clinical disease severity in MS.

Variability of Resting-State Functional MRI Graph Theory Metrics across 3T Platforms.

Graph theory analysis of brain connectivity data is a promising tool for studying the function of the healthy and diseased brain. The consistency of resting-state functional MRI (rsfMRI) connectivity measures across multiple scanner types is an important factor in designing multi-institutional research studies and has important implications for the potential use of this technique in a heterogeneous clinical setting. We sought to quantitatively study the interscanner variability of rsfMRI graph theory metrics obtained from healthy volunteers scanned on three different scanner platforms. In this prospective Institutional Review Board approved study, 9 healthy volunteers were enrolled for brain MRI on three 3T scanners (Magnetom Prisma, Skyra, and Trio, Siemens, Erlangen, Germany) in three separate scan sessions within approximately 1 week. Standard preprocessing of rsfMRI was performed with SPM12. Subject scans were normalized to Montreal Neurologic Institute (MNI) space, and connectivity of 116 regions-of-interests based on the automated anatomic labeling (AAL) atlas was calculated using Conn toolbox. Whole-network graph theory metrics were calculated using Brain Connectivity Toolbox, and intraclass correlation (ICC) across three scan sessions was assessed. A total of 25 rsfMRI exams were completed in 9 subjects with a median-intersession time of 3 days. Among all three sessions, there was good to excellent agreement in characteristic path length and global efficiency (ICC: .79, .79) and good agreement in the transitivity, local efficiency, and clustering coefficient (ICC=.72, .69, .62). There was high consistency of graph theory metrics of rsfMRI connectivity networks among healthy volunteers scanned on three different generation 3T MRI scanners.

Rapid Radial T1 and T2 Mapping of the Hip Articular Cartilage With Magnetic Resonance Fingerprinting.

Quantitative MRI can detect early changes in cartilage biochemical components, but its routine clinical implementation is challenging. To introduce a novel technique to measure T1 and T2 along radial sections of the hip for accurate and reproducible multiparametric quantitative cartilage assessment in a clinically feasible scan time. Reproducibility, technical validation. A seven-compartment phantom and three healthy volunteers. A novel MR pulse sequence that simultaneously measures proton density (PD), T1 , and T2 at 3 T was developed. Automatic positioning and semiautomatic cartilage segmentation were implemented to improve consistency and simplify workflow. Intra- and interscanner variability of our technique was assessed over multiple scans on three different MR scanners. For each scan, the median of cartilage T1 and T2 over six radial slices was calculated. Restricted maximum likelihood estimation of variance components was used to estimate intrasubject variances reflecting variation between results from the two scans using the same scanner (intrascanner variance) and variation among results from the three scanners (interscanner variance). The estimation error for T1 and T2 with respect to reference standard measurements was less than 3% on average for the phantom. The average interscanner coefficient of variation was 1.5% (1.2-1.9%) and 0.9% (0.0-3.7%) for T1 and T2 , respectively, in the seven compartments of the phantom. Total scan time in vivo was 7:13 minutes to obtain PD, T1 , and T2 maps along six radial hip sections at 0.6 × 0.6 × 4.0 mm3 voxel resolution. Interscanner variability for the in vivo study was 1.99% and 5.46% for T1 and T2 , respectively. in vivo intrascanner variability was 1.15% for T1 and 3.24% for T2 . Our method, which includes slice positioning, model-based parameter estimation, and cartilage segmentation, is highly reproducible. It could enable employing quantitative hip cartilage evaluation for longitudinal and multicenter studies. 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:810-815.

Repeatability and reproducibility of variable flip angle T1 quantification in the prostate at 3 T.

Variable flip angle (VFA) imaging is widely used for the estimation of T1 relaxation in the prostate, but may have limited repeatability and reproducibility due to its sensitivity to B1 + inhomogeneity. To assess the repeatability and reproducibility of prostate T1 estimation with and without compensating for B1 + variation. Prospective. Twenty-one volunteers were prospectively recruited and scanned twice on two 3 T MRI scanners, resulting in 84 VFA T1 exams. 3 T/2D saturated turbo fast low angle shot (FLASH) and 3D dual-echo FLASH. Two B1 + mapping techniques, including reference region VFA (RR-VFA) and saturated turbo FLASH (satTFL), were used for B1 + correction, and T1 maps with and without B1 + correction were tested for intrascanner repeatability and interscanner reproducibility. Volumetric regions of interest (ROIs) were drawn on the transition zone, peripheral zone of the prostate, and the obturator internus left and right muscles in the corresponding slices. The average T1 within each ROI for each scan was compared for both intra- and interscanner variability using concordance correlation coefficient and a Bland-Altman plot. Both RR-VFA-corrected T1 and satTFL-corrected T1 showed higher intra- and interscanner correlation (0.89/0.87 and 0.87/0.84, respectively) than VFA T1 (0.84 and 0.74). Bland-Altman plots showed that VFA T1 had wider 95% limits of agreement and a larger range of T1 for each tissue compared with T1 with B1 + correction. The application of B1 + correction (both RR-VFA and satTFL) to VFA T1 results in more repeatable and reproducible T1 estimation than VFA T1 . This can potentially provide improved quantification of the prostate dynamic contrast-enhanced MRI parameters. Level of Evidence 1. Technical Efficacy Stage 1. J. Magn. Reson. Imaging 2018.

Impact of automatically detected motion artifacts on coronary calcium scoring in chest computed tomography.

The amount of coronary artery calcification (CAC) quantified in computed tomography (CT) scans enables prediction of cardiovascular disease (CVD) risk. However, interscan variability of CAC quantification is high, especially in scans made without ECG synchronization. We propose a method for automatic detection of CACs that are severely affected by cardiac motion. Subsequently, we evaluate the impact of such CACs on CAC quantification and CVD risk determination. This study includes 1000 baseline and 585 one-year follow-up low-dose chest CTs from the National Lung Screening Trial. About 415 baseline scans are used to train and evaluate a convolutional neural network that identifies observer determined CACs affected by severe motion artifacts. Therefore, 585 paired scans acquired at baseline and follow-up were used to evaluate the impact of severe motion artifacts on CAC quantification and risk categorization. Based on the CAC amount, the scans were categorized into four standard CVD risk categories. The method identified CACs affected by severe motion artifacts with 85.2% accuracy. Moreover, reproducibility of CAC scores in scan pairs is higher in scans containing mostly CACs not affected by severe cardiac motion. Hence, the proposed method enables identification of scans affected by severe cardiac motion, where CAC quantification may not be reproducible.

Enhanced Quantification of Retinal Perfusion by Improved Discrimination of Blood Flow From Bulk Motion Signal in OCTA.

PurposeQuantification of optical coherence tomography angiography (OCTA) is confounded by the prevalence of bulk motion. We have previously developed a regression-based bulk motion subtraction (rb-BMS) algorithm that estimates bulk motion velocity and corrects for its effect on flow signal. Here, we aim to investigate its ability to improve the reliability of capillary density (CD) quantification.MethodsTwo spectral-domain systems (70-kHz Avanti/AngioVue and 68-kHz Cirrus/AngioPlex) acquired 6 × 6-mm OCTA scans. The rb-BMS algorithm was applied on each OCTA volume. Regression analysis of angiographic versus reflectance signal of avascular A-lines in B-frames was used to set an optimized reflectance-adjusted threshold for discriminating vascular versus nonvascular voxels. The CD was calculated from en face maximum projections of the superficial vascular complex in macular scans and the nerve fiber layer plexus in disc scans, excluding large vessels. The retinal signal strength (RSS) was calculated by averaging the logarithmic-scale OCT reflectance signal, and its correlation with CD was investigated.ResultsEight healthy eyes were scanned with each instrument on 2 separate days. The rb-BMS algorithm improved within-visit repeatability and between-visit reproducibility of CD compared with a global-threshold measurement algorithm. Using the rb-BMS algorithm, the CD results were less affected by RSS and the population variation was reduced. Motion-induced line artifacts were also reduced.ConclusionsThe rb-BMS algorithm improved the reliability of perfusion quantification in OCTA on both Food and Drug Administration–cleared spectral-domain OCTA systems.Translational RelevanceThe rb-BMS method helped reduce the inter-scan variability by generating accurate vessel maps, improving the reliability of retinal perfusion quantification.

326. PET scanner qualification for clinical trial: Comparison between Italian and worldwide experience

Purpose The aim of this work was to compare the results obtained by the procedure for qualifying PET/CT scanners for Clinical Trial Qualification (CTQ) adopted by the Italian Foundation on Lymphoma (FIL), the Grupo Espanol de Linfomas/Transplante Autologo de Medula Osea (GELTAMO) and the International Extranodal Lymphoma Study Group (IELSG). Methods Uniformity (UQP) and image quality (IQ) NEMA/IEC phantoms filled with 18F and acquired by local personnel were uploaded to a central server and analyzed within the CoreLab. Background activity concentration in UQP (BACUQP), Background activity concentration (BACIQ) and sphere to background ratio (SBR) in the IQ phantom were compared to expected values. Variability of these indexes among different PET/CT scanners was estimated in term of inter-scanner variability (ISV) at 95% confidence level. Results The number of PET/CT site qualified and the number of iteration necessary for the CTQ are summarized in Table 1. The BACUQP ISV at 95% confidence level among different scanners were 21.5%, 20.9% and 20.3% for Italian, Spanish and Worldwide PET/CT respectively. The BACIQ ISV were 63.0%, 36.4% and 40.4% and the SBR ISV were 57.9%, 57.5% and 35.5% for Italian, Spanish and Worldwide PET/CT, respectively. Conclusions The CTQ is a robust and reproducible procedure to verify inter-scanner calibration. The BACUQP is at least two times smaller than BACIQ demonstrating that the uniformity phantom, that is used for CTQ, is more accurately prepared by local sites. SBR demonstrated a great variability (ISV from about 35.5% to 57.9%) because it accounts both for variability in phantom preparation and in reconstruction algorithm tuning.

49 Performance Assessment of Magnetic Resonance Imaging (MRI) pelvimetry using ex vivo anatomic pieces and a 3D-printed geometric-distortion phantom

Introduction Feto-maternal morbidity and mortality increase with prolonged labor which can be related with fetalpelvic disproportion. Pelvimetric imaging is useful for assessing the eligibility of vaginal delivery in patients suspected of having disproportion [1] . Commonly performed using Computed Tomography (CT), pelvimetry is being increasingly done in MRI in order to tackle issues of ionizing-radiation exposure and take advantage of the rich contrast provided in MRI [2] . Nonetheless, MR images can be subjected to geometric distortions because of hardware design limitations [3] . Such distortions may impair MRIpelvimetric measurements. In this study, we assessed the accuracy of MRI-pelvimetry compared with CTpelvimetry using ex-vivo pelvises and a 3D-printed geometric-distortion phantom. Method We scanned ten ex-vivo pelvises on a CT scanner (Siemens Sensation) using the implemented clinical low-dose (LD-CT) and high-dose (HD-CT) pelvimetry protocol. MRI was performed on four 1.5T MRI scanners (Siemens Avanto, GE Signa, Philips Achieva, Toshiba Elan). Pelvises were scanned in sagittal and oblique axial using T1-, T2-weighted FSE and T1-weighted SPGR sequences. A trained radiologist performed pelvimetry measurements. Pelvic inlet and outlet anteroposterior diameters were measured using sagittal images. Pelvic inlet and outlet transverse diameters were measured using oblique axial images. For data analysis, MRI measurements were compared with CT using Bland-Altman plots and discrepancy analysis. MRI measurements were also analyzed for inter-scanner variability. Geometric distortion (GD) measurement: we used a custom previously-published methodology which relies on a 3D-printed phantom made up of 3621 control points which are 5 mm-diameter spheres equally spaced within a cylinder (diameter = length = 170 mm) [4] . GD images were acquired on the Siemens Avanto MR unit with and without the manufacturer’s correction that is available but commonly unused by clinical teams. Results The discrepancy between LD-CT and HD-CT measurements was up to 10%. The discrepancy between MRI and LD-CT was up to 11%. As for MRI and HD-CT, the discrepancy was up to 7%. MRI inter-scanner variation was up to 8%. As for geometric distortions, measurements were −1.4 mm Conclusion For pelvimetry purposes, our preliminary results show that MRI is as much accurate as high-dose CT and outperforms low-dose CT. We also show that geometric distortions can be minimized in MR images by using the implemented corrections. Hence MRI pelvimetry appears as an excellent alternative to CT pelvimetry in an endeavor to reduce fetuses exposure to ionizing radiation. Upcoming works in this study include assessment of interobserver reproducibility with the intervention of a second radiologist and geometric distortion measurement on the three remaining MRI scanners.

The Canadian Dementia Imaging Protocol: Harmonizing National Cohorts.

Harmonized protocols to collect imaging data must be devised, employed, and maintained in multicentric studies to reduce interscanner variability in subsequent analyses. To present a standardized protocol for multicentric research on dementia linked to neurodegeneration in aging, harmonized on all three major vendor platforms. The protocol includes a common procedure for qualification, quality control, and quality assurance and feasibility in large-scale studies. Prospective. The study involved a geometric phantom, a single individual volunteer, and 143 cognitively healthy, mild cognitively impaired, and Alzheimer's disease participants in a large-scale, multicentric study. MRI was perform with 3T scanners (GE, Philips, Siemens) and included 3D T1 w, PD/T2 w, , T2 w-FLAIR, diffusion, and BOLD resting state acquisitions. Measures included signal- and contrast-to-noise ratios (SNR and CNR, respectively), total brain volumes, and total scan time. SNR, CNR, and scan time were compared between scanner vendors using analysis of variance (ANOVA) and Tukey tests, while brain volumes were tested using linear mixed models. Geometric phantom T1 w SNR was significantly (P < 0.001) higher in Philips (mean: 71.4) than Siemens (29.5), while no significant difference was observed between vendors for T2 w (32.0 and 37.2, respectively, P = 0.243). Single individual volunteer T1 w CNR was higher in subcortical regions for Siemens (P < 0.001), while Philips had higher cortical CNR (P = 0.044). No significant difference in brain volumes was observed between vendors (P = 0.310/0.582/0.055). The average scan time was 41.0 minutes (SD: 2.8) and was not significantly different between sites (P = 0.071) and cognitive groups (P = 0.853). The harmonized Canadian Dementia Imaging Protocol suits the needs of studies that need to ensure quality MRI data acquisition for the measurement of brain changes across adulthood, due to aging, neurodegeneration, and other etiologies. A detailed description, exam cards, and operators' manual are freely available at the following site: www.cdip-pcid.ca. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:456-465.

Evaluation of Intra- and Interscanner Reliability of MRI Protocols for Spinal Cord Gray Matter and Total Cross-Sectional Area Measurements.

BackgroundIn vivo quantification of spinal cord atrophy in neurological diseases using MRI has attracted increasing attention.PurposeTo compare across different platforms the most promising imaging techniques to assess human spinal cord atrophy.Study TypeTest/retest multiscanner study.SubjectsTwelve healthy volunteers.Field Strength/SequenceThree different 3T scanner platforms (Siemens, Philips, and GE) / optimized phase sensitive inversion recovery (PSIR), T1‐weighted (T1‐w), and T2*‐weighted (T2*‐w) protocols.AssessmentOn all images acquired, two operators assessed contrast‐to‐noise ratio (CNR) between gray matter (GM) and white matter (WM), and between WM and cerebrospinal fluid (CSF); one experienced operator measured total cross‐sectional area (TCA) and GM area using JIM and the Spinal Cord Toolbox (SCT).Statistical TestsCoefficient of variation (COV); intraclass correlation coefficient (ICC); mixed effect models; analysis of variance (t‐tests).ResultsFor all the scanners, GM/WM CNR was higher for PSIR than T2*‐w (P < 0.0001) and WM/CSF CNR for T1‐w was the highest (P < 0.0001). For TCA, using JIM, median COVs were smaller than 1.5% and ICC >0.95, while using SCT, median COVs were in the range 2.2–2.75% and ICC 0.79–0.95. For GM, despite some failures of the automatic segmentation, median COVs using SCT on T2*‐w were smaller than using JIM manual PSIR segmentations. In the mixed effect models, the subject was always the main contributor to the variance of area measurements and scanner often contributed to TCA variance (P < 0.05). Using JIM, TCA measurements on T2*‐w were different than on PSIR (P = 0.0021) and T1‐w (P = 0.0018), while using SCT, no notable differences were found between T1‐w and T2*‐w (P = 0.18). JIM and SCT‐derived TCA were not different on T1‐w (P = 0.66), while they were different for T2*‐w (P < 0.0001). GM area derived using SCT/T2*‐w versus JIM/PSIR were different (P < 0.0001).Data ConclusionThe present work sets reference values for the magnitude of the contribution of different effects to cord area measurement intra‐ and interscanner variability. Level of Evidence: 1 Technical Efficacy: Stage 4J. Magn. Reson. Imaging 2019;49:1078–1090.

Radiation Dose Reduction at Pediatric CT: Use of Low Tube Voltage and Iterative Reconstruction.

Given the growing awareness of and concern for potential carcinogenic effects of exposure of children to ionizing radiation at CT, optimizing acquisition parameters is crucial to achieve diagnostically acceptable image quality at the lowest possible radiation dose. Among currently available dose reduction techniques, recent technical innovations have allowed the implementation of low tube voltage scans and iterative reconstruction (IR) techniques into daily clinical practice for pediatric CT. The benefits of lowering tube voltage include a considerable reduction in radiation dose and improved contrast on images, especially when an iodinated contrast medium is used. The increase in noise, which is attributed to decreased photon penetration, is a major drawback but is not as severe as that at adult CT because of the small body size of children. In addition, use of IR algorithms can suppress increased noise, yielding wider applicability for low tube voltage scans. However, a careful implementation strategy and methodologic approach are necessary to maximize the potential for dose reduction while preserving diagnostic image quality under each clinical condition. The potential pitfalls of and topics related to these techniques include (a) the effect of tube voltage on the surface radiation dose, (b) the effect of window settings, (c) accentuation of metallic artifacts, (d) deterioration of low contrast detectability at low-dose settings, (e) interscanner variation of x-ray spectra, and (f) a comparison with the use of a spectral shaping technique. Appropriate use of low tube voltage and IR techniques is helpful for radiation dose reduction in most applications of pediatric CT. Online DICOM image stacks are available for this article . ©RSNA, 2018.

Assessment of quantitative magnetic resonance imaging metrics in the brain through the use of a novel phantom

ABSTRACTObjective: Multisite and longitudinal neuroimaging studies are important in uncovering trajectories of recovery and neurodegeneration following traumatic brain injury (TBI) and concussion through the use of diffusion tensor imaging (DTI) and other imaging modalities. This study assessed differences in anisotropic diffusion measurement across four scanners using a human and a novel phantom developed in conjunction with the Chronic Effects of Neurotrauma Consortium.Method: Human scans provided measurement within biological tissue, and the novel physical phantom provided measures of anisotropic intra-tubular diffusion to serve as a model for intra-axonal water diffusion. Intra- and inter-scanner measurement variances were compared, and the impact on effect size was calculated.Results: Intra-scanner test–retest reliability estimates for fractional anisotropy (FA) demonstrated relative stability over testing intervals. The human tissue and phantom showed similar FA ranges, high linearity and large within-device effect sizes. However, inter-scanner measures of FA indicated substantial differences, some of which exceeded typical DTI effect sizes in mild TBI.Conclusion: The diffusion phantom may be used to better elucidate inter-scanner variability in DTI-based measurement and provides an opportunity to better calibrate results obtained from scanners used in multisite and longitudinal studies. Novel solutions are being evaluated to understand and potentially overcome these differences.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P43. FDG-PET/CT for assessment of pain perception and correlation to clinical outcome following surgery for lumbar disc herniation

BACKGROUND CONTEXT Pain perception seems to be highly individual and diverse, depending on multiple factors. Musculoskeletal pain, and especially back pain, has great socio-economic impact, as it often leads to prolonged periods of sick leave and an increased use of analgesic medicine, especially opioids. PURPOSE Using FDG-PET/CT, this study tries to visualize and quantify basal ganglia activity in the brain and subsequently correlate with patient pain perception and clinical outcome. STUDY DESIGN/SETTING Consecutive series of patients from a cingle-center, multisurgeon, teritiary spine practice. PATIENT SAMPLE Consecutive series of patients scheduled for spine surgery. OUTCOME MEASURES Oswestry Disability Index (ODI), EuroQol-5D (EQ-5D), Visual Analog Scale (VAS) for back and leg pain (0 to100), Cold Pressor Test (CPT), Pressure Pain Respons (PPR) and Chemical Pain Response with Saline Injection. METHODS A total of 28 patients aged 40-65years, found eligible for surgery due to first-time lumbar disc herniation (LDH) were included in an ongoing study, where FDG-PET/CT was performed preoperatively and 6 weeks and 6 months following operation. Using a standardized protocol for quantitative sensory testing (QST), patients’ pain perception and tolerance was also collected. All patients followed normal surgical procedure and postoperative regime. The thalamus was selected as region of interest and marked using both ROVER (ABX, Radeberg, Germany) and OsiriX (Pixmeo SARL, Bernex, Switzerland) software. Cerebellum was used as reference to eliminate inter-scan variability. Comparison was made between the three time points and lateralization was evaluated. Correlations between quantitative measures of the thalamus and clinical data (PROM and QST) were also made. RESULTS Patients with LDH often present with unilateral radiating pain, and, therefore, a lateralization pattern in the shape of increased FDG uptake in the contralateral thalamus was expected. Using quantitative measures of thalamic activity, we found distinct lateralization of activity corresponding with the side of radicular pain (p-value .01). Preoperatively, patients with a higher lateralization of SUVmean in thalamus had a decreased tolerance to pain perception in the lumbar area (correlation coefficient 0.40, p-value .05). Six weeks postoperatively, patients presenting with a higher level of lateralization had significantly decreased pain tolerability over a wide variety of stimuli, and their ability to tolerate temperature stimulus was also decreased (correlation coefficient −0.47, p-value .02). The same pattern was found 6 months postoperatively with multiple significant correlations. CONCLUSIONS FDG-PET/CT may be used to some degree to correlate pain perception and distinct cerebral changes in metabolism; however, current methods of measurement do not yet allow for clinical application. Measures on pain perception and cerebral changes in metabolism may – with further development of modalities – have something to offer in the clinical setting.

Interstudy reproducibility of dark blood high-resolution MRI in evaluating basilar atherosclerotic plaque at 3 Tesla.

We aimed to evaluate the interscan, intraobserver, and interobserver reproducibility of basilar atherosclerotic plaque employing dark blood high-resolution magnetic resonance imaging (HR-MRI) at 3 Tesla. Sixteen patients (14 males and 2 females) with > 30% basilar stenosis as identified by conventional magnetic resonance angiography were prospectively recruited for scan and rescan examinations on a 3 Tesla MRI system using T2-weighted turbo spin-echo protocol. Two observers independently measured the areas of vessels and lumens. Wall area was derived by subtracting the lumen area from the vessel area. Areas of vessels, lumens and walls were compared for the evaluation of interscan variability of basilar plaque. To assess the intraobserver variability, one observer reevaluated all the images of the first scan after a 4-week interval. Fourteen patients were included in the final analysis. No clinically significant difference was observed for interscan, intraobserver, and interobserver measurements. The intraclass correlations for vessel, lumen, and wall areas were excellent and ranged from 0.973 to 0.981 for the interscan measurements, 0.997 to 0.998 for the intraobserver measurements and 0.979 to 0.985 for the interobserver measurements. The coefficients of variation for quantitative basilar morphology measurements were 4.31%-10.35% for the interscan measurements, 1.41%-4.62% for the intraobserver measurements and 3.79%-8.46% for the interobserver measurements. Compared with the interscan and interobserver measurements, narrow intervals of the scatterplots were observed for the intraobserver measurements by Bland-Altman plots. Basilar atherosclerotic plaque imaging demonstrates excellent reproducibility at 3 Tesla. The study proves that dark blood HR-MRI may serve as a reliable tool for clinical studies focused on the progression and treatment response of basilar atherosclerosis.