COVID-19 Stroke Apical Lung Examination Study 2: a national prospective CTA biomarker study of the lung apices, in patients presenting with suspected acute stroke (COVID SALES 2).

BACKGROUND: Apical ground-glass opacification (GGO) identified on CT angiography (CTA) performed for suspected acute stroke was developed in 2020 as a coronavirus-disease-2019 (COVID-19) diagnostic and prognostic biomarker in a retrospective study during the first wave of COVID-19. OBJECTIVE: To prospectively validate whether GGO on CTA performed for suspected acute stroke is a reliable COVID-19 diagnostic and prognostic biomarker and whether it is reliable for COVID-19 vaccinated patients. METHODS: In this prospective, pragmatic, national, multi-center validation study performed at 13 sites, we captured study data consecutively in patients undergoing CTA for suspected acute stroke from January-March 2021. Demographic and clinical features associated with stroke and COVID-19 were incorporated. The primary outcome was the likelihood of reverse-transcriptase-polymerase-chain-reaction swab-test-confirmed COVID-19 using the GGO biomarker. Secondary outcomes investigated were functional status at discharge and survival analyses at 30 and 90 days. Univariate and multivariable statistical analyses were employed. RESULTS: CTAs from 1,111 patients were analyzed, with apical GGO identified in 8.5 % during a period of high COVID-19 prevalence. GGO showed good inter-rater reliability (Fleiss κ = 0.77); and high COVID-19 specificity (93.7 %, 91.8-95.2) and negative predictive value (NPV; 97.8 %, 96.5-98.6). In subgroup analysis of vaccinated patients, GGO remained a good diagnostic biomarker (specificity 93.1 %, 89.8-95.5; NPV 99.7 %, 98.3-100.0). Patients with COVID-19 were more likely to have higher stroke score (NIHSS (mean +/- SD) 6.9 +/- 6.9, COVID-19 negative, 9.7 +/- 9.0, COVID-19 positive; p = 0.01), carotid occlusions (6.2 % negative, 14.9 % positive; p = 0.02), and larger infarcts on presentation CT (ASPECTS 9.4 +/- 1.5, COVID-19 negative, 8.6 +/- 2.4, COVID-19 positive; p = 0.00). After multivariable logistic regression, GGO (odds ratio 15.7, 6.2-40.1), myalgia (8.9, 2.1-38.2) and higher core body temperature (1.9, 1.1-3.2) were independent COVID-19 predictors. GGO was associated with worse functional outcome on discharge and worse survival after univariate analysis. However, after adjustment for factors including stroke severity, GGO was not independently predictive of functional outcome or mortality. CONCLUSION: Apical GGO on CTA performed for patients with suspected acute stroke is a reliable diagnostic biomarker for COVID-19, which in combination with clinical features may be useful in COVID-19 triage.

Comparison of [18F] FDG-PET/MRI and Clinical Findings for Assessment of Suspected Lumbar Facet Joint Pain: A Prospective Study to Characterize Candidate Nonanatomic Imaging Biomarkers and Potential Impact on Management.

BACKGROUND AND PURPOSE: Prior retrospective studies have suggested that both T2 hyperintensity and gadolinium enhancement on fat-suppressed MR imaging are associated with lumbar facet joint pain, but prospective evaluation of FDG-PET/MR imaging with a standardized protocol and correlation to clinical findings are lacking. The primary aim was to prospectively assess a standardized FDG-PET/MRI protocol in patients with suspected facetogenic low back pain, with determination of the concordance of imaging and clinical findings. MATERIALS AND METHODS: Ten patients with clinically suspected facetogenic low back pain were prospectively recruited with a designation of specific facet joints implicated clinically. Subsequently, patients underwent an FDG-PET/MR imaging examination with gadolinium. Each facet joint was graded for perifacet signal change on MR imaging and FDG activity. The frequency and correlation of MR imaging, FDG-PET, and clinical findings were determined. RESULTS: FDG activity showed high concordance with high overall MR imaging scores (concordance correlation coefficient = 0.79). There was concordance of the clinical side of pain with the side of high overall MR imaging scores and increased FDG activity on 12/20 (60%) sides. Both a high overall MR imaging score (concordance correlation coefficient = 0.12) and FDG-PET findings positive for increased activity (concordance correlation coefficient = 0.10) had low concordance with the specific clinically implicated facet joints. Increased FDG activity or high MR imaging scores or both were present in only 10/29 (34%) facet joints that had been clinically selected for percutaneous intervention. Eleven (11%) facet joints that had not been selected for treatment demonstrated these imaging findings. CONCLUSIONS: There was low concordance of perifacet signal change and FDG activity with clinically implicated facet joints. This could indicate either the potential to change patient management or a lack of biomarker accuracy. Therefore, additional larger randomized studies with the use of comparative medial branch blocks would be useful to further investigate the clinical utility of these findings.

Effects of age on the glucose metabolic changes in mild cognitive impairment.

BACKGROUND AND PURPOSE: Decreased glucose metabolism in the temporal and parietal lobes on FDG-PET is recognized as an early imaging marker for the AD pathology. Our objective was to investigate the effects of age on FDG-PET findings in aMCI. MATERIALS AND METHODS: Twenty-five patients with aMCI at 55-86 years of age (median = 73 years) and 25 age- and sex-matched CN subjects underwent FDG-PET. SPM5 was used to compare the FDG uptake in patients in aMCI-old (>73 years) and aMCI-young (

Scatter and attenuation correction for brain SPECT using attenuation distributions inferred from a head atlas.

UNLABELLED: Sequential transmission scanning (TS)/SPECT is impractical for neurologically impaired patients who are unable to keep their heads motionless for the extended duration of the combined scans. To provide an alternative to TS, we have developed a method of inferring-attenuation distributions (IADs), from SPECT data, using a head atlas and a registration program. The validity of replacing TS with IAD was tested in 10 patients with mild dementia. METHODS: TS was conducted with each patient using a collimated 99mTc line source and fanbeam collimator; this was followed by hexamethyl propyleneamine oxime-SPECT. IAD was derived by deformably registering the brain component of a digital head atlas to a preliminary SPECT reconstruction and then applying the resulting spatial transformation to the full head atlas. SPECT data were reconstructed with scatter and attenuation correction. Relative regional cerebral blood flow was quantified in 12 threshold-guided anatomic regions of interest, with cerebellar normalization. SPECT reconstructions using IAD were compared with those using TS (which is the "gold standard") in terms of these regions of interest. RESULTS: When we compared all regions of interest across the population, the correlation between IAD-guided and TS-guided SPECT scans was 0.92 (P < 0.0001), whereas the mean absolute difference between the scans was 7.5%. On average, IAD resulted in slight underestimation of relative regional cerebral blood flow; however, this underestimation was statistically significant for only the left frontal and left central sulcus regions (P = 0.001 and 0.002, respectively). Error analysis indicated that approximately 10.0% of the total error was caused by IAD scatter correction, 36.6% was caused by IAD attenuation correction, 27.0% was caused by discrepancies in region-of-interest demarcation from quantitative errors in IAD-guided reconstructions, and 26.5% was caused by patient motion throughout the imaging procedure. CONCLUSION: SPECT reconstructions guided by IAD are sufficiently accurate to identify regional cerebral blood flow deficits of 10%, which are typical in moderate and advanced dementia.

Quality of life in assisted living homes: a multidimensional analysis.

This study examined the impact of four domains upon the quality of life (QOL) of senior residents living in assisted living homes: (a) demographic characteristics and health status, (b) social involvement, (c) facility characteristics, and (d) the social climate. Participants were 201 residents with functional impairments living in 55 different assisted living facilities in California. QOL was measured with three scales of depression, life satisfaction, and facility satisfaction. Bivariate correlations and ANOVAs found significant relations between at least one of the QOL measures and age, health status, social and family involvement measures, facility characteristics, and social climate measures. Social climate measures of cohesion, conflict, and independence had the strongest zero-order correlations. Regression analyses for the three QOL measures found cohesion to be the strongest predictor in all three regressions. Other QOL predictors in the regression analyses were fewer health conditions, participation in social activities, monthly family contact, and an environment low in conflict. Findings suggest that assisted living homes can improve resident QOL by creating a cohesive social environment, and encouraging social participation and family involvement.

The relationships among serum lipid levels, adiposity, and depressive symptomatology in persons aging with spinal cord injury.

BACKGROUND: Cardiovascular disease (CVD) appears to occur prematurely in persons with spinal cord injury (SCI). Stress may play a significant role in the development of CVD. Depression is the most common form of stress complicating the care of persons with SCI. METHODS: In 188 persons with SCI, 46% with tetraplegia and 54% with paraplegia, the relationship between depression and the serum lipid profile was studied. Depression was measured by the Older Adult Health and Mood Questionnaire (OAHMQ) for persons with disability. Total cholesterol, high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol and triglycerides were measured; body mass index (BMI) was computed and percent body fat was determined by dual-energy x-ray absorptiometry (DXA). RESULTS: Depression and level of SCI were found to have significant interactive effects on serum lipid levels. Serum total and LDL cholesterol, as well as triglycerides, were all higher among persons with paraplegia who were depressed compared to those who were not depressed. This was not found in persons with tetraplegia. Inverse relationships were evident between serum triglycerides and HDL cholesterol levels. Persons with paraplegia who were depressed had significantly more adiposity than those not depressed. BMI correlated directly with serum triglycerides and indirectly with serum HDL cholesterol. CONCLUSION: Depression appears to be a strong determinant of adverse lipid profiles in patients with paraplegia. association between depression and adiposity in these patients compounds the risk for cardiovascular disease.

Is immobilization associated with an abnormal lipoprotein profile? Observations from a diverse cohort.

OBJECTIVE: The potential effects of ethnicity, gender, and adiposity on the serum lipid profile in persons with spinal cord injury (SCI) were determined. SUBJECTS: Subjects with SCI were recruited during their annual physical examination from Rancho Los Amigos Medical Center, Downey, California. Sedentary able-bodied controls were Bridge and Tunnel Officers of the Triboro Bridge and Tunnel Authority of the New York City metropolitan area. METHODS: Serum lipid profiles were investigated in 320 subjects with SCI and compared to those obtained from 303 relatively sedentary able-bodied controls. Serum lipid studies were obtained in the fasting state. Data were collected between 1993 and 1996. All lipid determinations were performed by the same commercial laboratory. MAIN OUTCOME MEASURES: The dependent variables were the values from the lipid profile analysis. The independent variables consisted of study group, gender, ethnic group, age, duration of injury, and anthropometric measurements. RESULTS: The serum high-density lipoprotein cholesterol (HDL-c) level was reduced in the SCI compared with the control group (mean+/-SEM) (42+/-0.79 vs 47+/-0.67 mg/dl, P<0.0005). The serum HDL-c level was significantly lower in males with SCI than males in the control group (39+/-0.83 vs 45+/-0.70 mg/dl, P<0.0001), but not for females (51+/-1.54 vs 54 1.52 mg/dl, n.s.). Within the subgroups for whites and Latinos, HDL-c values were also lower in subjects with SCI than in controls (whites: 41+/-1.02 vs 46+/-0.86 mg/dl, P<0.0001; Latinos: 37+/-1.53 vs 42+/-1.59 mg/dl, P<0.05), but not for African Americans (49+/-1.56 vs 51+/-1.27 mg/dl, n.s.). African Americans had higher HDL-c values than whites or Latinos (SCI: 49+/-1.56 vs 41+/-1.02 or 37+/-1.53 mg/dl, P< 0.0001; controls: 51+/-1.27 vs 46+/-0.86 mg/dl, P<0.01 or 42+/-1.59 mg/dl, P<0.0005). In persons with SCI, the serum HDL-c values were inversely related to body mass index and estimated per cent body fat (r=0.27, P<0.0001). CONCLUSION: In white and Latino males, but not in females or African Americans, immobilization from SCI appears to be associated with lower HDL-c values than in controls.

Depression and life satisfaction among people ageing with post-polio and spinal cord injury.

PURPOSE AND BACKGROUND: Attention has recently begun to focus on the ageing of individuals with disability, not only as a long-term follow-up issue but as a unique developmental issue itself. The majority of individuals with an onset of disability before age 30 can now expect to live into their 60s, 70s and beyond. Most of the secondary medical conditions that foreshortened life expectancy have been controlled and improved rehabilitation techniques have evolved over the last 50 years. The average age of persons with post-polio in the United States is over 50 and the average age of persons with spinal cord injury is in the late 40s. New medical, functional and psychosocial problems have been discovered among persons ageing with these and other disabilities. Most of these problems lack sufficient scientific explanation, and therefore, clinical interventions. Quality of life (QOL) issues become involved as these changes occur. From a psychological perspective, QOL can be either positive, as reflected in high life satisfaction, or negative, as reflected in distress and depression. METHODS: This study reports on life satisfaction and depression in 360 persons, 121 with post-polio, 177 with SCI and 62 non-disabled age-matched comparisons. The Geriatric Depression Scale and the Older Adult Health and Mood Questionnaire assess depressive symptomatology and a 10-item life satisfaction scale with four-point ratings on each item used. RESULTS: Life satisfaction varied by the group, with the non-disabled group higher than one or both of the other two groups on all scales and the post-polio group higher than the SCI group on six scales. Satisfaction with health, finances, work and overall life were most different. 22% of the post-polio group, 41% of the SCI group and 15% of the non-disabled group had at least significant repressive symptomatology. CONCLUSION: The results for each group are discussed in terms of their relation to other coping variables that were assessed, particularly social support and coping methods.

Quality of life while aging with a disability.

Being able to develop or maintain a positive, or high, quality of life (QOL) after a disability is one of the most important outcomes from rehabilitation. Negative, or low, QOL may also occur, especially when people return to the community. Furthermore, as people with disability age, many experience changes in their health and functioning that challenge their hard-won QOL. This article describes research on QOL among persons who are aging with a disability. Both positive and negative dimensions of QOL were studied. Being able to maintain community activities was significantly related to QOL. Current age and age at onset of disability played a nonsignificant role on negative QOL but were significantly related to positive QOL. Assistive technology can play a significant role in helping individuals who are aging with a disability to maintain valued activities and experiences.

Metabolic and endocrine changes in persons aging with spinal cord injury.

Persons with spinal cord injury (SCI) have secondary medical disabilities that impair their ability to function. With paralysis, dramatic deleterious changes in body composition occur acutely with further adverse changes ensuing with increasing duration of injury. Lean mass, composed of skeletal muscle and bone, is lost and adiposity is relatively increased. The body composition changes may be further exacerbated by associated reductions in anabolic hormones, testosterone, and growth hormone. Individuals with SCI also have decreased levels of activity. These body composition and activity changes are associated with insulin resistance, disorders in carbohydrate and lipid metabolism, and may be associated with premature cardiovascular disease. Although limited information is available, upper body exercise and cycle ergometry of the lower extremities by functional electrical stimulation (FES) have been reported to have a salutary effect on these body composition and metabolic sequelae of paralysis. Perhaps other innovative, externally mediated forms of active exercise of the paralyzed extremities will result in an increased functional capacity, metabolic improvement, and reduction of atherosclerotic vascular disease.

The relative contributions of scatter and attenuation corrections toward improved brain SPECT quantification.

Mounting evidence indicates that scatter and attenuation are major confounds to objective diagnosis of brain disease by quantitative SPECT. There is considerable debate, however, as to the relative importance of scatter correction (SC) and attenuation correction (AC), and how they should be implemented. The efficacy of SC and AC for 99mTc brain SPECT was evaluated using a two-compartment fully tissue-equivalent anthropomorphic head phantom. Four correction schemes were implemented: uniform broad-beam AC, non-uniform broad-beam AC, uniform SC + AC, and non-uniform SC + AC. SC was based on non-stationary deconvolution scatter subtraction, modified to incorporate a priori knowledge of either the head contour (uniform SC) or transmission map (non-uniform SC). The quantitative accuracy of the correction schemes was evaluated in terms of contrast recovery, relative quantification (cortical:cerebellar activity), uniformity ((coefficient of variation of 230 macro-voxels) x 100%), and bias (relative to a calibration scan). Our results were: uniform broad-beam (mu = 0.12 cm(-1)) AC (the most popular correction): 71% contrast recovery, 112% relative quantification, 7.0% uniformity, +23% bias. Non-uniform broad-beam (soft tissue mu = 0.12 cm(-1)) AC: 73%, 114%, 6.0%, +21%, respectively. Uniform SC + AC: 90%, 99%, 4.9%, +12%, respectively. Non-uniform SC + AC: 93%, 101%, 4.0%, +10%, respectively. SC and AC achieved the best quantification; however, non-uniform corrections produce only small improvements over their uniform counterparts. SC + AC was found to be superior to AC; this advantage is distinct and consistent across all four quantification indices.

The effect of residual neurological deficit on serum lipoproteins in individuals with chronic spinal cord injury.

Subjects with spinal cord injury (SCI) have been shown to have an adverse lipid profile. Prior studies performed with smaller numbers of subjects have not been able to demonstrate any relationship between the level and degree of the neurological deficit and plasma lipid levels. Over a 2 year period we investigated the lipid profiles in 541 subjects from Rancho Los Amigos Medical Center, Downey, California. Subjects were grouped by tetraplegia (Tetra; n = 247) or paraplegia (Para; n = 294) and by subgroup for degree of neurological deficit: complete Tetra (n = 156), incomplete Tetra (n = 91), complete Para (n = 206) and incomplete Para (n = 88). The serum high-density lipoprotein (HDL) cholesterol level was lower in the Tetra than in the Para group (38 +/- 0.7 vs 45 +/- 0.8, P < 0.01). The group with Tetra had a higher percentage of subjects with serum HDL cholesterol values < 35 mg/dL [an independent risk factor for coronary heart disease (CHD)] than those with Para (38% vs 21%, P < 0.0001). A significant inverse relationship was found for degree of neurological deficit and mean serum HDL cholesterol level (r = 0.19, P < 0.001), with the greater the deficit, the lower the serum HDL cholesterol level. Serum total cholesterol levels were higher in the Para group than in the Tetra group (198 +/- 2.6 vs 184 +/- 2.6, P < 0.01). However, the ratio of total cholesterol to HDL cholesterol (a discriminator of risk for CHD) was significantly lower in the Para group than the Tetra group (4.8 vs 5.2%, P < 0.01). Thus, in persons with SCI a spectrum of depressed serum HDL cholesterol levels and increased cardiovascular risk occur, with the most adverse lipid changes correlating with the severity of neurological deficit.

Importance of bone attenuation in brain SPECT quantification.

UNLABELLED: The purpose of this study was to determine the effects of nonuniform attenuation on relative quantification in brain SPECT and to compare the ability of the Chang and Sorenson uniform attenuation corrections (UACs) to achieve volumetric relative quantification. METHODS: Three head phantoms (dry human skull, Rando and Radiology Support Devices (RSD) phantoms) were compared with a human head using a gamma camera transmission CT (gammaTCT) SPECT system and x-ray CT. Subsequently, the RSD phantom's brain reservoir was filled with a uniform water solution of 99mTc, and SPECT and gammaTCT data were acquired using fanbeam collimation. The attenuating effects of bone, scalp and head-holder in individual projections were determined by an analytical projection technique using the SPECT and gammaTCT reconstructions. The Chang UAC used brain and head contours that were segmented from the gammaTCT reconstruction to demarcate its attenuation map, whereas the Sorenson UAC fit slice-specific ellipses to the SPECT projection data. For each UAC, volumetric relative quantification was measured with varying attenuation coefficients (mus) of the attenuation map. RESULTS: Gamma camera transmission CT and x-ray CT scans showed that the dry skull and Rando phantoms suffered from a dried trabecular bone compartment. The RSD phantom most closely reproduced the attenuation coefficients of the human gammaTCT and x-ray CT scans. The analytical projections showed that the attenuating effects of bone, scalp and head-holder were nonuniform across the projections and accounted for 18%-37% of the total count loss. Volumetric relative quantification was best achieved with the Chang (zero iterations) attenuation correction using the head contour and mu = 0.075 cm(-1); however, cortical activity was found to be 10% higher than cerebellar activity. For all UACs, the optimal choices of mu were experimentally found to be lower than the recommended 0.12 cm(-1) for brain tissue. This result is theoretically supported here. CONCLUSION: The magnitude of errors resulting from uniform attenuation corrections can be greater than the magnitudes of regional cerebral blood flow deficits in patients with dementia, as compared with normal controls. This suggests that nonuniform attenuation correction in brain SPECT imaging must be applied to accurately estimate regional cerebral blood flow.

Multicenter trial validation of a camera-based method to measure Tc-99m mercaptoacetyltriglycine, or Tc-99m MAG3, clearance.

PURPOSE: To evaluate an improved camera-based method for calculating the clearance of technetium-99m mercaptoacetyltriglycine (MAG3) in a multicenter trial. MATERIALS AND METHODS: Tc-99m MAG3 scintigraphy was performed in 49 patients at three sites in the United States and Canada. The percentage of the injected dose of Tc-99m MAG3 in the kidney at 1-2, 1.0-2.5, and 2-3 minutes after injection was correlated with the plasma-based Tc-99m MAG3 clearances. The data were combined with the results obtained in 20 additional patients in a previously published pilot study. RESULTS: Regression models correlating the plasma-based Tc-99m MAG3 clearance with the percentage uptake in the kidney for each time interval were developed; there was no statistically significant difference among sites in the regression equations. Correction for body surface area statistically significantly (P < .005) improved the correlation coefficient for each time interval. For the 1.0-2.5-minute interval, the body surface area-corrected correlation coefficient for the four combined sites was .87, and it improved to .93 when one outlier was omitted from the analysis. Similar results were obtained with the other time intervals. Independent processing by two observers showed no clinically important differences in the percentage dose in the kidney or in relative function. CONCLUSION: An improved camera-based method to calculate the clearance of Tc-99m MAG3 was validated in a multicenter trial.

Depression and life satisfaction in aging polio survivors versus age-matched controls: relation to postpolio syndrome, family functioning, and attitude toward disability.

OBJECTIVE: To compare depressive symptoms and life satisfaction in aging polio survivors with age-matched controls and to relate these outcomes to scores to psychosocial and disability-related variables. DESIGN: A planned medical, functional, and psychosocial study with multivariate analyses. SETTING: A large, urban rehabilitation center. PARTICIPANTS: A volunteer sample of 121 polio survivors and an age-matched control group of 60 people with similar sociodemographic backgrounds. MAIN OUTCOMES: Depression as measured by the Geriatric Depression Scale and an 11-item life satisfaction scale. RESULTS: The prevalence of depressive disorders was not significantly different in the two groups, although the postpolio group tended to have more symptomatology and an overall depressive disorder prevalence of 28%. Some life satisfaction scale scores were significantly lower in the postpolio group, especially those concerned with health. People with postpolio syndrome scored significantly higher on depression scales and lower on some life satisfaction scales than people with a history of polio but without postpolio syndrome. Several psychosocial variables, most notably family functioning and attitude toward disability, helped to mediate this effect. Among people with significant depression, there was little, evidence of adequate treatment in the community. CONCLUSIONS: Postpolio by itself does not relate to higher depression scores or lower life satisfaction. Postpolio syndrome has some relation to depression, but family functioning and attitude toward disability are more important. There is a need for better community-based psychological services.

The Older Adult Health and Mood Questionnaire: a measure of geriatric depressive disorder.

Depressive disorders are a common problem in late life, requiring consistent and reliable screening by clinicians. Such screening should be based upon the most recent criteria available to facilitate diagnostic and nosologic agreement. This study presents a new screening instrument for geriatric depressive disorders based upon DSM-III-R criteria and the known differences in the display of depression that occur among older persons. The Older Adult Health and Mood Questionnaire (OAHMQ) is a 22-item questionnaire with sound psychometric properties and high validity. Its validation included comparisons with diagnostic assessments by geriatrically-trained psychiatrists and psychologists, and factor analysis. Using a three-part division of "normal," "clinically significant depressive symptoms," and "probable major depression," its sensitivity is .80 and its specificity is .87 for major depression, and .92 and .87, respectively, for any depressive disorder. Separate scoring of affective symptoms versus other symptoms of depression (i.e., physiologic, cognitive, or behavioral) can be useful for diagnostic and research purposes.

The geometric modulation transfer function of a transmission imaging system that uses a SPECT scintillation camera and parallel hole collimation.

An analytic expression has been derived to calculate the geometric modulation transfer function of a transmission imaging system that uses parallel hole collimation for both the source and the SPECT camera. This expression describes the resolution of the transmission imaging system and replaces the need to use computer intensive Monte Carlo simulations for the system design. The geometric modulation transfer function, denoted as MTFg(rho) = [A2sc(Ssc rho)**A2cc(Scc rho)]D(rho), where ** denotes two-dimensional convolution; Asc(rho) and Acc(rho) are the Fourier transforms (FT) of the aperture functions for the parallel hole source collimator (SC) and the camera collimator (CC) holes, respectively; D(rho) is the FT of the camera response; and ssc and scc are scaling constants that depend on the respective collimator dimensions, the system dimensions, the object distance above camera collimator and whether MTFg(rho) is calculated for the object or image plane. The theoretical MTFg(rho) was verified with Monte Carlo simulations and experimental results. The formalism shows that the system resolution is characterized by the camera resolution and a combination of the resolutions of the source and camera collimators. This expression can be used to optimize the design of transmission imaging systems to be used in nuclear medicine.

Transmission computed tomography imaging of the head with a SPECT system and a collimated line source.

UNLABELLED: Transmission images of relatively high resolution as compared to SPECT are needed for brain SPECT quantification to provide skull thickness, attenuation coefficients and anatomical correlation. Consequently, a technique to acquire transmission CT images with a SPECT system by using a collimated line source positioned at the focal line of a fanbeam collimator (FBC) has been developed. METHODS: Computer simulations that model the transmission imaging system optimized the system resolution and tested the validity of a equation for the geometric efficiency of the line source collimator (LSC). Based on the computer simulations, a LSC was constructed with tantalum septa 100 mm long, 0.5 mm thick and spaced 1.0 mm apart. A 600-mm focal length FBC was used. Experiments were conducted to measure the system resolution and to determine the effect of the LSC on the amount of detected scatter. RESULTS: The simulations showed that without a LSC the transmission images have a longitudinal resolution (LR) characterized by the resolutions of the FBC (depth-dependent, approximately 8 mm FWHM at 150 mm) and the detector (approximately 4 mm). However, with an optimally designed LSC, the contribution of the FBC to the system resolution can be made negligible, creating a system with a LR that is comparable to the detector resolution and independent of object depth. Resolution experiments conducted with a lucite rod phantom showed that the LR and TR are better than 4.8 mm and confirmed the results of the computer simulations. CONCLUSION: Brain transmission images of relatively high isotropic resolution can be obtained using a SPECT system, a FBC and an optimized LSC.