Optimisation of CT protocols in PET-CT across different scanner models using different automatic exposure control methods and iterative reconstruction algorithms

Background A significant proportion of the radiation dose from a PET-CT examination is dependent on the CT protocol, which should be optimised for clinical purposes. Matching protocols on different scanners within an imaging centre is important for the consistency of image quality and dose. This paper describes our experience translating low-dose CT protocols between scanner models utilising different automatic exposure control (AEC) methods and reconstruction algorithms. Methods The scanners investigated were a newly installed Siemens Biograph mCT PET with 64-slice SOMATOM Definition AS CT using sinogram affirmed iterative reconstruction (SAFIRE) and two GE Discovery 710 PET scanners with 128-slice Optima 660 CT using adaptive statistical reconstruction (ASiR). Following exploratory phantom work, 33 adult patients of various sizes were scanned using the Siemens scanner and matched to patients scanned using our established GE protocol to give 33 patient pairs. A comparison of volumetric CT dose index (CTDIvol) and image noise within these patient pairs informed optimisation, specifically for obese patients. Another matched patient study containing 27 patient pairs was used to confirm protocol matching. Size-specific dose estimates (SSDEs) were calculated for patients in the second cohort. With the acquisition protocol for the Siemens scanner determined, clinicians visually graded the images to identify optimal reconstruction parameters. Results In the first matched patient study, the mean percentage difference in CTDIvol for Siemens compared to GE was − 10.7% (range − 41.7 to 50.1%), and the mean percentage difference in noise measured in the patients’ liver was 7.6% (range − 31.0 to 76.8%). In the second matched patient study, the mean percentage difference in CTDIvol for Siemens compared to GE was − 20.5% (range − 43.1 to 1.9%), and the mean percentage difference in noise was 19.8% (range − 27.0 to 146.8%). For these patients, the mean SSDEs for patients scanned on the Siemens and GE scanners were 3.27 (range 2.83 to 4.22) mGy and 4.09 (range 2.81 to 4.82) mGy, respectively. The analysis of the visual grading study indicated no preference for any of the SAFIRE strengths. Conclusions Given the different implementations of acquisition parameters and reconstruction algorithms between vendors, careful consideration is required to ensure optimisation and standardisation of protocols.

Afraid of the dark: Light acutely suppresses activity in the human amygdala

Light improves mood. The amygdala plays a critical role in regulating emotion, including fear-related responses. In rodents the amygdala receives direct light input from the retina, and light may play a role in fear-related learning. A direct effect of light on the amygdala represents a plausible mechanism of action for light’s mood-elevating effects in humans. However, the effect of light on activity in the amygdala in humans is not well understood. We examined the effect of passive dim-to-moderate white light exposure on activation of the amygdala in healthy young adults using the BOLD fMRI response (3T Siemens scanner; n = 23). Participants were exposed to alternating 30s blocks of light (10 lux or 100 lux) and dark (<1 lux), with each light intensity being presented separately. Light, compared with dark, suppressed activity in the amygdala. Moderate light exposure resulted in greater suppression of amygdala activity than dim light. Furthermore, functional connectivity between the amygdala and ventro-medial prefrontal cortex was enhanced during light relative to dark. These effects may contribute to light’s mood-elevating effects, via a reduction in negative, fear-related affect and enhanced processing of negative emotion.

4400 Low CD4 nadir linked to widespread cortical thinning in adults with HIV

OBJECTIVES/GOALS: The history of immune suppression, especially CD4 nadir, has been shown to be a strong predictor of HIV-associated neurocognitive disorders (HAND). However, the potential mechanism of this association is not well understood. This study examined the relationship between CD4 nadir and brain atrophy. METHODS/STUDY POPULATION: Fifty-nine people with HIV participated in the cross-sectional study (mean age, 56.5 ± 5.8; age range, 41-69; 15 females; 46 African-Americans). High resolution structural MRI images were obtained using a 3T Siemens scanner. From a comprehensive 7-domain neuropsychological test battery, a global deficit score (GDS) and HAND diagnoses were determined for each participant. The correlation between CD4 nadir (the lowest ever lymphocyte CD4 count) and cortical thickness was investigated using a vertex-wise non-parametric approach with a conservative statistical threshold of p < 0.05 (FWE-corrected). RESULTS/ANTICIPATED RESULTS: Out of the 59 participants, 12 met standard Frascati criteria for asymptomatic neurocognitive impairment (ANI) and two met the criteria for mild neurocognitive disorder (MND). Across all participants, low CD4 nadir was associated with widespread cortical thinning, especially in the frontal and temporal regions. Higher GDS (indicating worse global neurocognitive function) was associated with bilateral frontal cortical thinning, and the association largely persisted in the subset of participants who did not meet HAND criteria. DISCUSSION/SIGNIFICANCE OF IMPACT: These results suggest that the low CD4 nadir may be associated with widespread neural injury in the brain, especially in the frontal and temporal regions. This spatial profile might contribute to the prevalence/phenotypes of HAND in the cART era, such as the frequently observed deficits in the executive domain.

MON-110 Utilization of GluCEST, a Novel Neuroimaging Technique, to Characterize the Brain Phenotype in Hyperinsulinism/Hyperammonemia Syndrome

BACKGROUND: Hyperinsulinism/Hyperammonemia (HI/HA) syndrome is the second most common form of congenital hyperinsulinism. It is caused by gain-of-function mutations in glutamate dehydrogenase (GDH), a mitochondrial enzyme expressed in pancreatic β-cells, liver, kidney, and brain, and is responsible for metabolizing glutamate into α-ketoglutarate and ammonia. In addition to hyperinsulinemic hypoglycemia due to abnormal GDH activity in pancreatic β-cells, ~80% of patients have developmental delays, learning, or behavioral disorders and &gt;60% have atypical absence seizures (Bahi-Buisson, 2008). These neurologic symptoms are not fully explained by hypoglycemia and are hypothesized to result from central nervous system (CNS) glutamate imbalance due to CNS GDH overactivity. Newer magnetic resonance imaging (MRI) techniques have allowed for sensitive estimation of CNS glutamate using Glutamate Chemical Exchange Saturation Transfer (GluCEST). We aimed to comprehensively characterize the biochemical and clinical neurologic phenotype of HI/HA leveraging GluCEST MRI. Methods: Subjects with confirmed HI/HA diagnosis and without contraindication to MRI had electroencephalogram (EEG), serum ammonia, and the following validated neurodevelopmental assessments: ABAS-3, BRIEF, and ASEBA CBCL (if &lt;18 years) or ASR (if &gt;18 years) completed. GluCEST MRI axial hippocampal and midsagittal slices were acquired on a 7.0T Siemens scanner and reported as GluCEST % contrast. Healthy control GluCEST % contrast data were obtained from a separate study using the same neuroimaging protocol. Results: 8 HI/HA subjects (4 female; mean age 28 years [range 16-56] years) participated to date. Median serum ammonia was 58 umol/L (IQR 39-89). 50% self-reported learning impairments and 37.5% self-reported prior ADHD diagnosis. Marked unilateral increase in hippocampal GluCEST % contrast was observed in 3/6 subjects (2 L&gt;R; 1 R&gt;L). Overall, median peak GluCEST % contrast level was significantly higher in HI/HA subjects than controls (10.3% [IQR 8.9-11.3] v. 8.0% [IQR 7.8-8.4], p=0.0013, n=6). Conclusions: This is the first study to evaluate CNS glutamate via GluCEST in HI/HA. Hippocampal glutamate, measured by GluCEST % contrast, was significantly higher in HI/HA subjects than healthy controls. Laterality in hippocampal glutamate was observed in half of subjects. These findings are remarkable given the known role of abnormal glutamate signaling in the development of epilepsy and neurocognitive impairment. Next steps are to complete midsagittal GluCEST image processing, EEG and neurodevelopmental assessment interpretations to explore correlations between CNS phenotype and brain glutamate pattern. GluCEST holds promise for elucidating the pathophysiology of CNS manifestations in HI/HA syndrome.

S163. GLUTAMATERGIC METABOLITES IN THE PSYCHOSIS SPECTRUM: FROM HIGH RISK SAMPLES TO FIRST EPISODE PSYCHOSIS

Background The N-methyl-D-aspartate receptor hypofunction model of schizophrenia suggests that dysfunction of these receptors leads to an excess release of glutamate and could explain the brain structural abnormalities characterizing these patients. However, glutamatergic pathways underlying transition to psychosis are yet unclear. Methods Youth with recent onset psychosis (FEP), within the first 5 years of disease, individuals with high risk for psychosis (HR) –including participants with psychosis risk syndrome meeting SIPS/SOPS criteria and offspring of parents with bipolar disorder or schizophrenia –, and healthy volunteers, were recruited and scanned with a 3T Siemens scanner. Magnetic resonance spectroscopy was performed using a 2x2x2 cm3 voxel (VOI) placed in the middle frontal region. Ratios of glutamate (Glu), and glutamate + glutamine (Glx) were quantified using LCModel. Results 18 adolescents with FEP, 33 HR and 32 healthy controls (HC) were included in the analysis. There were no significant differences between groups in mean age (16.4±2.1 vs 15.7±2.7 vs 16.8±1.9; F=2.0, p=.139), but there were trend-level differences in gender (%females: 33.3% vs 57.6% vs 68.8%; Х2=5.9, p=.052). Multivariate models controlling for gender showed a trend-level effect of group in Glu (F=2.9, p=.062), but not in Glx. Post-hoc pairwise contrasts for Glu revealed significantly higher Glu levels in HR individuals (1.38±0.16) compared to FEP (1.27±0.20) and HC (1.31±0.15). Discussion Our findings support that increased Glu in the prefrontal cortex may index risk of psychosis from the early stages of the disease, during adolescence. Our observations suggest a possible hyperglutamatergia in premorbid stages that may normalize –or even decrease – after illness onset, possibly related to treatment or compensatory mechanisms. While requiring replication in a larger sample and including follow-up through transition in HR individuals, our findings raise the possibility that abnormal glutamatergic metabolism in the prefrontal cortex could be used as a potential biomarker of illness and putative treatment target.

Reproducibility of calcium scoring of the coronary arteries: comparison between different vendors and iterative reconstructions

Background The coronary artery calcium scoring (CCS) has been widely used for cardiac risk stratification for asymptomatic patients. Purpose To assess the reproducibility of CCS performed on four different computed tomography (CT) scanners, and compare the variability between two reconstruction algorithms, filtered back projection (FBP), and iterative reconstruction (IR). Material and Methods A CCS phantom was made from agar and contained 23 pieces of chicken bones. The phantom was repeatedly scanned using four different CT scanners: Toshiba; GE; Philips; and Siemens. Images were reconstructed using FBP and IR. Agatston and volume scores of total bone fragments were calculated and the overall differences between the instruments were evaluated using the Friedman test. Comparison of the Agatston and volume scores between the two reconstruction algorithms, for each instrument, was evaluated using the Wilcoxon signed rank test. Results The difference in the Agatston scores was significantly different between the four machines ( P = 0.001). The Toshiba scanner yielded the highest score followed by Philips, GE, and Siemens scanners. There was no difference in the CCS evaluated using the two reconstruction algorithms, except in case of the Siemens scanner ( P = 0.032). Conclusion CCS performed on different scanners varied significantly. In the Toshiba, Philips, and GE scanners, there was no significant difference in the CCS determined using either an IR or the FBP algorithm. In the Siemens scanner, applying the IR algorithm resulted in a slightly different scores, which might not be clinically significant.

Setting pressure can change the size and shape of MRI artifacts caused by adjustable shunt valves: a study of the 4 newest models

OBJECTIVEAdjustable shunt valves that have been developed for the management of hydrocephalus all rely on intrinsically magnetic components, and artifacts with these valves on MRI are thus inevitable. The authors have previously reported that the shapes of shunt artifacts differ under different valve pressures with the proGAV 2.0 valve. In the present study the authors compared the size and shape of artifacts at different pressure settings with 4 new-model shunt valves.METHODSThe authors attached 4 new models of MRI-resistant shunt valve to the temporal scalp of a healthy volunteer: the proGAV 2.0; Codman Certas Plus; Polaris; and Strata MR. They set 3 different scales of pressures for each valve, depending on magnet orientation to the body axis. Artifacts were evaluated and compared among all valves on a 3.0-T GE scanner and 2 valves were also evaluated on a Philips scanner and a Siemens scanner. In-plane artifact sizes were evaluated as the maximum distance of the artifact from the expected scalp.RESULTSThe sizes and shapes of artifacts changed depending on valve pressure for all valves on the 3 different MRI scanners. Artifacts were less prominent on spin echo sequences than on gradient echo sequences. For diffusion-weighted imaging and time-of-flight MR angiography, the authors matched image numbers within the same sequence and compared appearances of artifacts. For all valves, the number of images affected by artifacts and the image number showing the largest artifact differed among valve settings.CONCLUSIONSArtifacts of all adjustable shunt valves showed gross changes corresponding to pressure setting. Not only the maximum distance of artifacts but also the shape changed significantly. The authors suggest that changing pressure settings offers one of the easiest ways to minimize artifacts on MRI.

A phantom study for the comparison of different brands of computed tomography scanners and software packages for endovascular aneurysm repair sizing and planning

Objectives Correct sizing of endoprostheses used for the treatment of abdominal aortic aneurysms is important to prevent endoleaks and migration. Sizing requires several steps and each step introduces a possible sizing error. The goal of this study was to investigate the magnitude of these errors compared to the golden standard: a vessel phantom. This study focuses on the errors in sizing with three different brands of computed tomography angiography scanners in combination with three reconstruction software packages. Methods Three phantoms with a different diameter, altitude and azimuth were scanned with three computed tomography scanners: Toshiba Aquilion 64-slice, Philips Brilliance iCT 256-slice and Siemens Somatom Sensation 64-slice. The phantom diameters were determined in the stretched view after central lumen line reconstruction by three observers using Simbionix PROcedure Rehearsal Studio, 3mensio and TeraRecon planning software. The observers, all novices in sizing endoprostheses using planning software, measured 108 slices each. Two senior vascular surgeons set the tolerated error margin of sizing on ±1.0 mm. Results In total, 11.3% of the measurements (73/648) were outside the set margins of ±1.0 mm from the phantom diameter, with significant differences between the scanner types (14.8%, 12.1%, 6.9% for the Siemens scanner, Philips scanner and Toshiba scanner, respectively, p-value = 0.032), but not between the software packages (8.3%, 11.1%, 14.4%, p-value = 0.141) or the observers (10.6%, 9.7%, 13.4%, p-value = 0.448). Conclusions It can be concluded that the errors in sizing were independent of the used software packages, but the phantoms scanned with Siemens scanner were significantly more measured incorrectly than the phantoms scanned with the Toshiba scanner. Consequently, awareness on the type of computed tomography scanner and computed tomography scanner setting is necessary, especially in complex abdominal aortic aneurysms sizing for fenestrated or branched endovascular aneurysm repair if appropriate the sizing is of upmost importance.

Assessment of Internal Jugular Vein Size in Healthy Subjects with Magnetic Resonance and Semiautomatic Processing

Background and Objectives. The hypothesized link between extracranial venous abnormalities and some neurological disorders awoke interest in the investigation of the internal jugular veins (IJVs). However, different IJV cross-sectional area (CSA) values are currently reported in literature. In this study, we introduced a semiautomatic method to measure and normalize the CSA and the degree of circularity (Circ) of IJVs along their whole length.Methods. Thirty-six healthy subjects (31.22 ± 9.29 years) were recruited and the 2D time-of-flight magnetic resonance venography was acquired with a 1.5 T Siemens scanner. The IJV were segmented on an axial slice, the contours were propagated in 3D. Then, IJV CSA and Circ were computed between the first and the seventh cervical levels (C1–C7) and normalized among subjects. Inter- and intrarater repeatability were assessed.Results. IJV CSA and Circ were significantly different among cervical levels (p<0.001). A trend for side difference was observed for CSA (larger right IJV,p=0.06), but not for Circ (p=0.5). Excellent inter- and intrarater repeatability was obtained for all the measures.Conclusion. This study proposed a reliable semiautomatic method able to measure the IJV area and shape along C1–C7, and suitable for defining the normality thresholds for future clinical studies.

Abstract 1961: Multi-Modality Comparison of Volumetric Quantification of Right Ventricular Volumes Using a Novel Semi-Automated Border Detection Software

Background. Right ventricular volumes (RVV) and ejection fraction (RVEF) measurements are challenging due to the complex shape of the right ventricle (RV). Current methods are tedious and have limited ability to take into account the base of the RV and right ventricular outflow tract. Novel semi-automated border detection software, RV analysis (RVA) was recently developed (TomTec) to overcome these limitations. Our goal was to determine whether there are inter-modality differences between real-time 3D echocardiographic (RT3DE), cardiac computed tomography (CCT) and cardiac magnetic resonance (CMR) data using the same RVA. Methods. We acquired transthoracic RT3DE images of the RV (Philips iE33 w/X4 probe) from the apical window using a full-volume mode in 12 patients referred for CMR imaging (1.5T Siemens scanner) and CCT (Toshiba) on the same day. CMR and CCT images were obtained in a stack of short-axis slices from RV base to apex, four-chamber and coronal views, and reformatted to obtain Cartesian volume data. All three types of images were analyzed to obtain end-systolic and end-diastolic volumes (ESV, EDV) and EF using RV analysis software (RVA). RT3DE and CCT were compared to CMR values as the reference standard, using linear regression and Bland-Altman analyses. Results. Analysis of RT3DE, CCT and CMR data were feasible in all patients. RT3DE and CCT RVV and RVEF correlated well with CMR (Table). CCT overestimated RVV whereas RT3DE underestimated RVV. Both CCT and RT3DE slightly underestimated RVEF compared to CMR. Conclusion. This new technique for volumetric RV surface detection applied to RT3DE and CCT data provides accurate RVV and RVEF measurements in agreement with CMR.