Performance comparison of a dedicated total breast PET system with a clinical whole-body PET system: a simulation study.

This paper presents a novel PET geometry for breast cancer imaging. The scanner consists of a 'stadium' (a rectangle with two semi-circles on opposite sides) shaped ring, along with anterior and posterior panels to provide high sensitivity and high spatial resolution for an imaging field-of-view (FOV) that include both breasts, mediastinum and axilla. We simulated this total-breast PET system using GATE and reconstructed the coincidence events using a GPU-based list-mode image reconstruction implementing maximum likelihood expectation-maximization (ML-EM) algorithm. The rear-panel is made up of a single layer of LSO crystals (3.2 × 3.2 × 20 mm3each), while the 'stadium'-shaped elongated ring and the anterior panel are made with dual-layered LSO crystals (1.6 × 1.6 × 6 mm3each). The energy resolution and coincidence resolving time of all detectors are assumed to be 12% and 250 ps full-width-at-half-maximum, respectively. Various sized simulated lesions (4, 5, 6 mm) having 4:1, 5:1, and 6:1 lesion-to-background radioactivity concentration ratios, mimicking different biological uptakes, were strategically located throughout a volumetric torso phantom. We compared system sensitivity and lesion detectability of the dedicated total-breast PET system to a state-of-the-art clinical whole-body PET scanner. The mean sensitivity of the total-breast PET system is 3.21 times greater than that of a whole-body PET scanner in the breast regions. The total-breast PET system also provides better contrast-recovery coefficients for lesions of all sizes and lesion-to-background ratios in the breast when compared to a reference clinical whole-body PET scanner. Receiver operating characteristics (ROC) study shows the area under the ROC curve is 0.948 and 0.924 for the total-breast system and the whole-body PET scanner, respectively, in the detection of 4 mm diameter lesions with 4:1 lesion-to-background ratio. This study demonstrates our novel geometry can provide an imaging FOV larger than conventional PEM systems to simultaneously image both breasts, chest wall and axillae with significantly improved lesion detectability in the breasts when compared to a whole-body PET scanner.

The QIBA Profile for FDG PET/CT as an Imaging Biomarker Measuring Response to Cancer Therapy.

The Quantitative Imaging Biomarkers Alliance (QIBA) Profile for fluorodeoxyglucose (FDG) PET/CT imaging was created by QIBA to both characterize and reduce the variability of standardized uptake values (SUVs). The Profile provides two complementary claims on the precision of SUV measurements. First, tumor glycolytic activity as reflected by the maximum SUV (SUVmax) is measurable from FDG PET/CT with a within-subject coefficient of variation of 10%-12%. Second, a measured increase in SUVmax of 39% or more, or a decrease of 28% or more, indicates that a true change has occurred with 95% confidence. Two applicable use cases are clinical trials and following individual patients in clinical practice. Other components of the Profile address the protocols and conformance standards considered necessary to achieve the performance claim. The Profile is intended for use by a broad audience; applications can range from discovery science through clinical trials to clinical practice. The goal of this report is to provide a rationale and overview of the FDG PET/CT Profile claims as well as its context, and to outline future needs and potential developments.

Comparison of Bayesian penalized likelihood reconstruction versus OS-EM for characterization of small pulmonary nodules in oncologic PET/CT.

OBJECTIVE: To determine whether the recently introduced Bayesian penalized likelihood PET reconstruction (Q.Clear) increases the visual conspicuity and SUVmax of small pulmonary nodules near the PET resolution limit, relative to ordered subset expectation maximization (OS-EM). METHODS: In this institutional review board-approved and HIPAA-compliant study, 29 FDG PET/CT scans performed on a five-ring GE Discovery IQ were retrospectively selected for pulmonary nodules described in the radiologist's report as "too small to characterize", or small lung nodules in patients at high risk for lung cancer. Thirty-two pulmonary nodules were assessed, with mean CT diameter of 8 mm (range 2-18). PET images were reconstructed with OS-EM and Q.Clear with noise penalty strength ß values of 150, 250, and 350. Lesion visual conspicuity was scored by three readers on a 3-point scale, and lesion SUVmax and background liver and blood pool SUVmean and SUVstdev were recorded. Comparison was made by linear mixed model with modified Bonferroni post hoc testing; significance cutoff was p < 0.05. RESULTS: Q.Clear improved lesion visual conspicuity compared to OS-EM at ß = 150 (p < 0.01), but not 250 or 350. Lesion SUVmax was increased compared to OS-EM at ß = 150 and 250 (p < 0.01), but not 350. CONCLUSION: In a cohort of small pulmonary nodules with size near an 8 mm PET full-width half maximum, Q.Clear significantly increased lesion visual conspicuity and SUVmax compared to our standard non- time-of-flight OS-EM reconstruction, but only with low noise penalization. Q.Clear with ß = 150 may be advantageous when evaluation of small pulmonary nodules is of primary concern.

Characterization of 3-Dimensional PET Systems for Accurate Quantification of Myocardial Blood Flow.

Three-dimensional (3D) mode imaging is the current standard for PET/CT systems. Dynamic imaging for quantification of myocardial blood flow with short-lived tracers, such as 82Rb-chloride, requires accuracy to be maintained over a wide range of isotope activities and scanner counting rates. We proposed new performance standard measurements to characterize the dynamic range of PET systems for accurate quantitative imaging. METHODS: 82Rb or 13N-ammonia (1,100-3,000 MBq) was injected into the heart wall insert of an anthropomorphic torso phantom. A decaying isotope scan was obtained over 5 half-lives on 9 different 3D PET/CT systems and 1 3D/2-dimensional PET-only system. Dynamic images (28 × 15 s) were reconstructed using iterative algorithms with all corrections enabled. Dynamic range was defined as the maximum activity in the myocardial wall with less than 10% bias, from which corresponding dead-time, counting rates, and/or injected activity limits were established for each scanner. Scatter correction residual bias was estimated as the maximum cavity blood-to-myocardium activity ratio. Image quality was assessed via the coefficient of variation measuring nonuniformity of the left ventricular myocardium activity distribution. RESULTS: Maximum recommended injected activity/body weight, peak dead-time correction factor, counting rates, and residual scatter bias for accurate cardiac myocardial blood flow imaging were 3-14 MBq/kg, 1.5-4.0, 22-64 Mcps singles and 4-14 Mcps prompt coincidence counting rates, and 2%-10% on the investigated scanners. Nonuniformity of the myocardial activity distribution varied from 3% to 16%. CONCLUSION: Accurate dynamic imaging is possible on the 10 3D PET systems if the maximum injected MBq/kg values are respected to limit peak dead-time losses during the bolus first-pass transit.

Quantitative differences in [(18)F] NaF PET/CT: TOF versus non-TOF measurements.

[(18)F] sodium fluoride (NaF) PET/CT is a current, clinically relevant method to assess bone metastases. Time-of-flight (TOF) PET provides better statistical data quality, which can improve either lower image noise or improve resolution, or both, depending on the image reconstruction. Improved resolution can improve quantitative measurements of standardized uptake value (SUV) in small structures. These quantitative differences may be important in both clinical interpretation and multicenter clinical trials where quantification is integral to assessing response to therapy. The purpose of this study is to determine if and by how much SUV quantitatively differs between TOF and conventional non-TOF reconstructions in [(18)F] NaF PET/CT. SUV measurements (mean and maximum) were compared in TOF and non-TOF [(18)F] NaF PET-CT reconstructions for 47 prostate cancer patients in normal regions including: soft tissue (n=282 total regions; liver, aorta, posterior abdominal fat, bladder, brain, and paraspinal muscles), and osseous structures (n=188; T12 vertebral body, femoral diaphyseal cortex, femoral head, and lateral rib). Comparisons were also made for benign degenerative changes (n=281) and metastases (n=159). TOF and non-TOF SUVs were assessed with paired t-test and linear correlations. Normal soft tissue showed lower SUVmean for TOF compared to non-TOF in liver, brain, and adipose. All osseous structures showed higher SUVmean for TOF compared to non-TOF including normal regions, degenerative joint disease, and metastases. For all metastatic lesions, the average SUVmean increased by 2.5%, and in degenerative joint disease it increased by 3.5% on TOF reconstructions. Smaller lesion size was a significant factor influencing this increase in SUVmean. TOF SUVmean values are higher in osseous structures and lower in background soft tissue structures. While these differences are statistically significant, the magnitudes of these changes are relatively modest. Smaller osseous lesions may have higher contrast and higher SUVmean values with TOF reconstruction compared to non-TOF reconstructions. The differences in TOF vs. non-TOF images should be considered when evaluating response to therapy and in the design of multi-center clinical trials.

Modulation of circulating angiogenic factors and tumor biology by aerobic training in breast cancer patients receiving neoadjuvant chemotherapy.

Aerobic exercise training (AET) is an effective adjunct therapy to attenuate the adverse side-effects of adjuvant chemotherapy in women with early breast cancer. Whether AET interacts with the antitumor efficacy of chemotherapy has received scant attention. We carried out a pilot study to explore the effects of AET in combination with neoadjuvant doxorubicin-cyclophosphamide (AC+AET), relative to AC alone, on: (i) host physiology [exercise capacity (VO2 peak), brachial artery flow-mediated dilation (BA-FMD)], (ii) host-related circulating factors [circulating endothelial progenitor cells (CEP) cytokines and angiogenic factors (CAF)], and (iii) tumor phenotype [tumor blood flow ((15)O-water PET), tissue markers (hypoxia and proliferation), and gene expression] in 20 women with operable breast cancer. AET consisted of three supervised cycle ergometry sessions/week at 60% to 100% of VO2 peak, 30 to 45 min/session, for 12 weeks. There was significant time × group interactions for VO2 peak and BA-FMD, favoring the AC+AET group (P < 0.001 and P = 0.07, respectively). These changes were accompanied by significant time × group interactions in CEPs and select CAFs [placenta growth factor, interleukin (IL)-1ß, and IL-2], also favoring the AC+AET group (P < 0.05). (15)O-water positron emission tomography (PET) imaging revealed a 38% decrease in tumor blood flow in the AC+AET group. There were no differences in any tumor tissue markers (P > 0.05). Whole-genome microarray tumor analysis revealed significant differential modulation of 57 pathways (P < 0.01), including many that converge on NF-κB. Data from this exploratory study provide initial evidence that AET can modulate several host- and tumor-related pathways during standard chemotherapy. The biologic and clinical implications remain to be determined.

Target localization using scanner-acquired SPECT data.

Target localization using single photon emission computed tomography (SPECT) and planar imaging is being investigated for guiding radiation therapy delivery. Previous studies on SPECT-based localization have used computer-simulated or hybrid images with simulated tumors embedded in disease-free patient images where the tumor position is known and localization can be calculated directly. In the current study, localization was studied using scanner-acquired images. Five fillable spheres were placed in a whole body phantom. Sphere-to-background 99mTc radioactivity was 6:1. Ten independent SPECT scans were acquired with a Trionix Triad scanner using three detector trajectories: left lateral 180°, 360°, and right lateral 180°. Scan time was equivalent to 4.5 min. Images were reconstructed with and without attenuation correction. True target locations were estimated from 12 hr SPECT and CT images. From the 12 hr SPECT scan, 45 sets of orthogonal planar images were used to assess target localization; total acquisition time per set was equivalent to 4.5min. A numerical observer localized the center of the targets in the 4.5 min SPECT and planar images. SPECT-based localization errors were compared for the different detector trajectories. Across the four peripheral spheres, and using optimal iteration numbers and postreconstruction smoothing, means and standard deviations in localization errors were 0.90 ± 0.25 mm for proximal 180° trajectories, 1.31 ± 0.51 mm for 360° orbits, and 3.93 ± 1.48 mm for distal 180° trajectories. This rank order in localization performance is predicted by target attenuation and distance from the target to the collimator. For the targets with mean localization errors < 2 mm, attenuation correction reduced localization errors by 0.15 mm on average. The improvement from attenuation correction was 1.0 mm on average for the more poorly localized targets. Attenuation correction typically reduced localization errors, but for well-localized targets, the detector trajectory generally had a larger effect. Localization performance was found to be robust to iteration number and smoothing. Localization was generally worse using planar images as compared with proximal 180° and 360° SPECT scans. Using a proximal detector trajectory and attenuation correction, localization errors were within 2 mm for the three superficial targets, thus supporting the current role in biopsy and surgery, and demonstrating the potential for SPECT imaging inside radiation therapy treatment rooms.

FDG-PET assessment of the effect of head and neck radiotherapy on parotid gland glucose metabolism.

PURPOSE: Functional imaging with [F-18]-fluorodeoxyglucose positron emission tomography (FDG-PET) provides the opportunity to define the physiology of the major salivary glands before and after radiation therapy. The goal of this retrospective study was to identify the radiation dose-response relationship of parotid gland glucose metabolism in patients with head and neck squamous cell carcinoma (HNSCC). MATERIALS AND METHODS: Forty-nine adults with HNSCC were identified who had curative intent intensity-modulated radiation therapy (IMRT) and FDG-PET imaging before and after treatment. Using a graphical user interface, contours were delineated for the parotid glands on axial CT slices while all authors were blinded to paired PET slices. Average and maximal standard uptake values (SUV) were measured within these anatomic regions. Changes in SUV and volume after radiation therapy were correlated with parotid gland dose-volume histograms from IMRT plans. RESULTS: The average parotid gland volume was 30.7 mL and contracted 3.9 ± 1.9% with every increase of 10 Gy in mean dose (p = 0.04). However, within the first 3 months after treatment, there was a uniform reduction of 16.5% ± 7.3% regardless of dose. The average SUV(mean) of the glands was 1.63 ± 0.48 pretreatment and declined by 5.2% ± 2.5% for every increase of 10 Gy in mean dose (p = 0.04). The average SUV(max) was 4.07 ± 2.85 pretreatment and decreased in a sigmoid manner with mean dose. A threshold of 32 Gy for mean dose existed, after which SUV(max) declined rapidly. CONCLUSION: Radiation dose responses of the parotid glands can be measured by integrated CT/FDG-PET scans. Retrospective analysis showed sigmoidal declines in the maximum metabolism but linear declines in the average metabolism of the glands with dose. Future studies should correlate this decline in FDG uptake with saliva production to improve treatment planning.

Analysis of pretreatment FDG-PET SUV parameters in head-and-neck cancer: tumor SUVmean has superior prognostic value.

PURPOSE: To evaluate the prognostic significance of different descriptive parameters in head-and-neck cancer patients undergoing pretreatment [F-18] fluoro-D-glucose-positron emission tomography (FDG-PET) imaging. PATIENTS AND METHODS: Head-and-neck cancer patients who underwent FDG-PET before a course of curative intent radiotherapy were retrospectively analyzed. FDG-PET imaging parameters included maximum (SUV(max)), and mean (SUV(mean)) standard uptake values, and total lesion glycolysis (TLG). Tumors and lymph nodes were defined on co-registered axial computed tomography (CT) slices. SUV(max) and SUV(mean) were measured within these anatomic regions. The relationships between pretreatment SUV(max), SUV(mean), and TLG for the primary site and lymph nodes were assessed using a univariate analysis for disease-free survival (DFS), locoregional control (LRC), and distant metastasis-free survival (DMFS). Kaplan-Meier survival curves were generated and compared via the log-rank method. SUV data were analyzed as continuous variables. RESULTS: A total of 88 patients was assessed. Two-year OS, LRC, DMFS, and DFS for the entire cohort were 85%, 78%, 81%, and 70%, respectively. Median SUV(max) for the primary tumor and lymph nodes was 15.4 and 12.2, respectively. Median SUV(mean) for the primary tumor and lymph nodes was 7 and 5.2, respectively. Median TLG was 770. Increasing pretreatment SUV(mean) of the primary tumor was associated with decreased disease-free survival (p = 0.01). Neither SUV(max) in the primary tumor or lymph nodes nor TLG was prognostic for any of the clinical endpoints. Patients with pretreatment tumor SUV(mean) that exceeded the median value (7) of the cohort demonstrated inferior 2-year DFS relative to patients with SUV(mean) ≤ the median value of the cohort, 58% vs. 82%, respectively, p = 0.03. CONCLUSION: Increasing SUV(mean) in the primary tumor was associated with inferior DFS. Although not routinely reported, pretreatment SUV(mean) may be a useful prognostic FDG-PET parameter and should be further evaluated prospectively.

Variable-time positron emission tomography leg protocol to equalize noise for positron emission tomography/computed tomography acquisitions.

OBJECTIVES: Positron emission tomography protocols conventionally use a constant scan time per bed position (BP). It may be optimal to spend more time scanning some body sections, particularly the more attenuating sections. The relatively consistent tapering of legs may allow a single, variable-time protocol that could reduce or redistribute time and equalize image quality throughout the leg. Reducing the total scan time will limit the opportunity for motion, which can reduce imaging artefacts and improves image fusion, will improve a patient's experience, and will yield the biggest gains in time for the tallest patients. METHODS: Leg dimensions were studied in 55 adult positron emission tomography/computed tomography scans. Image quality versus size was parameterized using bottle phantoms (diameters, 4.5-19.7 cm) filled with identical 18F-fluorodeoxyglucose concentrations, positioned as legs and imaged. An exponential relationship of diameter to noise was fit to the data, which defined the noise-equalizing, variable-time protocol. RESULTS: Of 55 patient leg studies, 94.5% (52/55) had leg diameters that were less than ± 7.5% of the mean leg diameter for other patients of similar height. To equalize noise throughout the leg, relative scan times from superior to inferior as a function of BP are (1, 0.65, 0.45, 0.36, 0.30, and 0.25). CONCLUSION: Variable time compared with a constant-time protocol can require 75% less time for some BPs and half the total acquisition time. A variable-time protocol to reduce time has been implemented.

A systematic review of the factors affecting accuracy of SUV measurements.

OBJECTIVE: There is growing interest in using PET/CT for evaluating early response to therapy in cancer treatment. Although widely available and convenient to use, standardized uptake value (SUV) measurements can be influenced by a variety of biologic and technologic factors. Many of these factors can be addressed with close attention to detail and appropriate quality control. This article will review factors potentially affecting SUV measurements and provide recommendations on ways to minimize when using serial PET to assess early response to therapy. CONCLUSION: Scanner and reconstruction parameters can significantly affect SUV measurements. When using serial SUV measurements to assess early response to therapy, imaging should be performed on the same scanner using the same image acquisition and reconstruction protocols. In addition, attention to detail is required for accurate determination of the administered radiopharmaceutical dose.

Kinetics of brain nicotine accumulation in dependent and nondependent smokers assessed with PET and cigarettes containing 11C-nicotine.

Tobacco smoking is a chronic, relapsing disorder that constitutes one of the primary preventable causes of death in developed countries. Two of the popular hypotheses to explain the development and maintenance of strong nicotine dependence in cigarette smokers posit (i) a rapid brain nicotine accumulation during cigarette smoking and/or (ii) puff-associated spikes in brain nicotine concentration. To address these hypotheses, we investigated the dynamics of nicotine accumulation in the smoker's brain during actual cigarette smoking using PET with 3-s temporal resolution and (11)C-nicotine loaded into cigarettes. The results of the study, performed in 13 dependent smokers (DS) and 10 nondependent smokers (NDS), suggest that puff-associated spikes in the brain nicotine concentration do not occur during habitual cigarette smoking. Despite the presence of a puff-associated oscillation in the rate of nicotine accumulation, brain nicotine concentration gradually increases during cigarette smoking. The results further suggest that DS have a slower process of brain nicotine accumulation than NDS because they have slower nicotine washout from the lungs and that DS have a tendency to compensate for their slower rate of brain nicotine accumulation compared with NDS by inhaling a larger volume of smoke. For these reasons, smokers' dependence on cigarette smoking, or the resistance of NDS to becoming dependent, cannot be explained solely by a faster brain nicotine accumulation.

Increasing uptake time in FDG-PET: standardized uptake values in normal tissues at 1 versus 3 h.

OBJECTIVE: Positron emission tomography (PET) imaging at more than 1 h after 2-deoxy-2-[(18)F]fluoro-D: -glucose (FDG) administration may result in less blood pool activity and possibly decreased normal FDG uptake in tissues such as liver. Lower normal background activity could be an important component of improved image contrast on delayed imaging. Increasing FDG uptake in normal organs, however, may mitigate the beneficial effects of blood pool clearance. The purpose of this study is to determine the normal tissue and blood pool FDG uptake at 1 and 3 h after injection. SUBJECTS AND METHODS: Ninety-nine patients with known or suspected malignancy referred for FDG-PET-computed tomography (CT) were retrospectively evaluated. PET imaging was performed at either 1 h (60 +/- 15 min; n = 50) or at 3 h (180 +/- 15 min; n = 49) after FDG administration. Normal tissue FDG uptake without involvement by malignancy or influenced by artifact (misregistration, "brown fat," focal muscle uptake, focal atherosclerotic disease) was confirmed by inspection of both the PET and CT scans. Aortic blood pool, adipose tissue, bone marrow, cerebellum, liver, lungs, muscle, and spleen were quantitatively evaluated by CT-guided region of interest analysis in three contiguous slices. Mean standardized uptake values (SUVs) were analyzed using one-way analysis of variance. RESULTS: Mean SUVs on the 3- versus 1-h images were significantly lower for aortic blood pool 13% (p < 0.0001) and adipose tissue 20% (p < 0.008). FDG uptake showed significant increases at 3 h compared to 1-h imaging in the cerebellum 40% (p < 0.0001), bone marrow 25% (p = 0.003), muscle 21% (p = 0.0004), and spleen 13% (p = 0.01). The liver and lung showed no significant differences (1%, p = 0.85; -2%, p = 0.62, respectively). CONCLUSIONS: On FDG imaging at 3 h compared to 1 h, significant changes were apparent, but the magnitude of changes was modest overall. Three-hour delayed imaging demonstrated significantly lower aortic blood pool and adipose tissue activity and significantly higher cerebellum, muscle, spleen, and bone marrow activity. Hepatic and lung activities were not significantly different. These results suggest that previously reported improvements in tumor image contrast with delayed imaging may be primarily due to cumulative FDG uptake within the tumor rather than reduction in normal background activity.

Evaluation of combined cardiac positron emission tomography and coronary computed tomography angiography for the detection of coronary artery disease.

BACKGROUND: Coronary artery disease is a leading cause of morbidity and mortality. Multiple imaging modalities are used to screen for significant coronary artery disease. We report the concordance between coronary computed tomography angiography (CTA) and stress cardiac positron emission tomography (CPET) to detect significant coronary artery disease, the feasibility of combining CTA and CPET in one diagnostic test, and the ability of CTA and CPET to detect significant coronary artery disease by comparison with cardiac catheterization. METHODS: Forty patients were prospectively enrolled and imaged with a hybrid PET/CT scanner. Eighteen patients had cardiac catheterization data for comparison. Concordance of findings between diagnostic tests was assessed by examining overall percentage in agreement, area under the receiver operating characteristic curve, sensitivity, specificity, and positive and negative predictive values. RESULTS: The overall agreement between CTA and CPET for detecting significant coronary artery disease was 76.3% with a sensitivity and specificity of 91.7 and 69.2%, respectively. The overall agreement between CTA and cardiac catheterization for detecting significant coronary artery disease was 81.3% with a sensitivity and specificity of 81.8 and 80.0%, respectively. The overall agreement between CPET and cardiac catheterization for detecting significant coronary artery disease was 77.8% with a sensitivity and specificity of 76.9 and 80.0%, respectively. CONCLUSION: CTA and CPET can be performed in a single diagnostic test interval to simultaneously assess the extent of coronary artery disease and its hemodynamic significance. The sensitivity and specificity of CTA and CPET are similar to existing noninvasive screening tests.

SPECT/CT physical principles and attenuation correction.

Using nuclear medicine techniques, physiologic activity and processes can be identified in a way that is unique from other modalities. Oftentimes it is helpful to know the exact location of the physiologic uptake that is visualized on a scan. Knowing the exact location can sometimes help to distinguish normal from abnormal physiologic uptake. When an abnormality has been identified, knowing the exact location can then be helpful in treatment planning. The ability to provide precise localization of physiologic data from nuclear medicine studies is now possible with hybrid SPECT/CT systems. Additionally, these systems provide an accurate attenuation correction of the nuclear medicine image data. After reading this article, the technologist will be able to list and describe the inherent problems associated with SPECT image acquisition and reconstruction, briefly explain how data acquired from the CT scanner are used to provide attenuation correction data for SPECT and anatomic information for diagnostic purposes, list and briefly describe the different types of clinical SPECT/CT systems, and discuss the importance of accurate CT and SPECT image registration.

Quantitative effects of contrast enhanced CT attenuation correction on PET SUV measurements.

PURPOSE: The presence of contrast materials on computed tomography (CT) images can cause problems in the attenuation correction of positron emission tomography (PET) images. These are because of errors converting the CT attenuation of contrast to 511-keV attenuation and by the change in tissue enhancement over the duration of the PET emission scan. Newer CT-based attenuation correction (CTAC) algorithms have been developed to reduce these errors. METHODS: To evaluate the effectiveness of the modified CTAC technique, we performed a retrospective analysis on 20 patients, comparing PET images using unenhanced and contrast-enhanced CT scans for attenuation correction. A phantom study was performed to simulate the effects of contrast on radiotracer concentration measurements. RESULTS: There was a maximum difference in calculated radiotracer concentrations of 5.9% within the retrospective data and 7% within the phantom data. CONCLUSION: Using a CTAC algorithm that de-emphasizes high-density areas, contrast-enhanced CT can be used for attenuation mapping without significant errors in quantitation.

Near-Field High-Energy Spectroscopic Gamma Imaging Using a Rotation Modulation Collimator.

Certain trace elements are vital to the body and elemental imbalances can be indicators of certain diseases including cancer and liver diseases. Neutron Stimulated Emission Computed Tomography (NSECT) is being developed as spectroscopic imaging technique to non-invasively and non-destructively measure and image elemental concentrations within the body. A region of interest is illuminated via a high-energy beam of neutrons that scatter inelastically with elemental nuclei within the body. The excited nuclei then relax by emitting characteristic gamma rays. Acquiring the gamma spectrum in a tomographic manner allows not only the identification of elements, but also the formation of images representing spatial distributions of specific elements. We are developing a high-energy position-sensitive gamma camera that allows full illumination of the entire region of interest. Because current scintillation crystal based position-sensitive gamma cameras operate in too low of an energy range, we are adapting high-energy gamma imaging techniques used in space-based imaging. A High Purity Germanium (HPGe) detector provides high-resolution energy spectra while a rotating modulation collimator (RMC) placed in front of the detector modulates the incoming signal to provide spatial information. The purpose of this manuscript is to describe the near-field RMC geometry, which varies greatly from the infinite-focus space-based applications, and how it modulates the incident gamma flux. A simple geometric model is presented and then used to reconstruct two-dimensional planar images of both simulated point sources and extended sources.

Left ventricular functional assessment in mice: feasibility of high spatial and temporal resolution ECG-gated blood pool SPECT.

PURPOSE: To prospectively determine feasibility of evaluating murine left ventricular (LV) function with electrocardiographically (ECG)-gated blood pool single photon emission computed tomography (SPECT). MATERIALS AND METHODS: All animal studies had institutional animal care and use committee approval. SPECT was performed with conventional time-binned acquisition (eight frames per ECG cycle) in normal mice (normal group A, n = 6) and mice with myocardial infarction (MI) (n = 8). To determine feasibility of high temporal resolution and rapid data acquisition, another group of normal mice (normal group B, n = 4) underwent imaging with conventional (eight-frame) time-binned and list-mode (LM) acquisitions. LM acquisitions were reconstructed with eight and 16 frames per ECG cycle and 10 minutes of data (short LM). SPECT images were assessed visually, and LV-to-lung background activity ratios were calculated. LV end-systolic and end-diastolic volumes were defined with a phase analysis and threshold method. LV ejection fraction (LVEF) was calculated from LV volumes and count-based methods (n = 18 mice). Fractional shortening (FS) at echocardiography defined MI dysfunction (mild MI: FS > or = 50%; severe MI: FS < 50%). Group means were compared for significant differences with analysis of variance. RESULTS: ECG-gated blood pool SPECT demonstrated normal, concentric LV contraction in all normal mice (n = 10). LV-to-lung background ratio was more than 10:1 (range, 10.3-29.4; n = 18). Focal wall motion abnormalities were detected at SPECT both visually and with phase analysis in all mice with severe MI (n = 5). Mice with severe MI had significantly lower LVEF than normal group A mice (32% +/- 14 [standard deviation] vs 64% +/- 8%; P < .001). All mice with mild MI (n = 3) had normal contraction and LVEF. In paired acquisitions in normal group B mice, all reconstructions (n = 16) showed normal LV contraction. LVEF was not significantly different (P = .88) between time-binned (71% +/- 12), eight-frame LM (71% +/- 12), 16-frame LM (77% +/- 10), and short LM (73% +/- 14) reconstructions. CONCLUSION: Murine LV functional assessment is feasible with high spatial and temporal resolution ECG-gated blood pool SPECT. LV dysfunction can be quantified and focal wall motion abnormalities detected in the MI model of heart failure.

Head and neck cancer: dedicated FDG PET/CT protocol for detection--phantom and initial clinical studies.

PURPOSE: To retrospectively compare the sensitivity of a dedicated fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) protocol versus a standard whole-body PET/CT protocol for detection of head and neck cancer, with biopsy and follow-up as reference standards. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. Dedicated and standard PET/CT protocols were performed in a phantom and in 55 patients suspected of having head and neck cancer (28 men, 27 women; age range, 21-79 years). The neck phantom contained four 4.4-9.8-mm-diameter spheres. Standard protocol consisted of a midcranium to proximal thigh emission scan of 2-4 minutes per bed position. Dedicated protocol was an 8-minute head and neck scan. Reconstructed field of view and pixel size, respectively, were 30 cm and 2.34 mm for the dedicated and 50 cm and 3.91 mm for the standard protocol. FDG uptake was evaluated visually and semiquantitatively by using standardized uptake values (SUVs). Mean SUV was compared between dedicated and standard protocols with a t test modified for clustered sampling. Receiver operating characteristic (ROC) curves were calculated. A two-tailed P value was used. RESULTS: In the phantom study, a larger percentage difference (20%-27%) in sphere-to-background ratios with the dedicated than with the standard protocol was observed for 6.0-9.8-mm spheres. In the clinical study, a total of 149 lymph nodes were identified. Five malignant and six benign lymph nodes (mean diameter, 7.1 mm) were visually identified with the dedicated protocol only. SUVs with the dedicated protocol were significantly higher than those with the standard protocol (P<.001). Area under the ROC curve was 0.94 for the dedicated and 0.92 for the standard protocol (P=.56). CONCLUSION: FDG PET with either the standard or dedicated protocol was more sensitive than CT for evaluating head and neck lymph nodes. The dedicated protocol improved the detectability of smaller nodes.

Regional brain activity correlates of nicotine dependence.

Fifteen smokers participated in a study investigating brain correlates of nicotine dependence. Dependence was reduced by having subjects switch to denicotinized cigarettes for 2 weeks while wearing nicotine skin patches. Positron emission tomography (PET) scans assessed regional cerebral metabolic rate for glucose (rCMRglc) after overnight nicotine abstinence on three occasions: (1) at baseline; (2) after 2 weeks of exposure to denicotinized cigarettes+nicotine patches; and (3) 2 weeks after returning to smoking the usual brands of cigarettes. Craving for cigarettes and scores on the Fagerström Test of Nicotine Dependence (FTND) questionnaire decreased at the second session relative to the first and last sessions. Regional brain metabolic activity (normalized to whole brain values) at session 2 also showed a significant decrease in the right hemisphere anterior cingulate cortex. Exploratory post hoc analyses showed that the change in craving across sessions was negatively correlated with the change in rCMRglc in several structures within the brain reward system, including the ventral striatum, orbitofrontal cortex and pons. The between-session difference in thalamus activity (right hemisphere) was positively correlated with the difference in FTND scores. Correlational analyses also revealed that reported smoking for calming effects was associated with a decrease (at session 2) in thalamus activity (bilaterally) and with an increase in amygdala activity (left hemisphere). Reported smoking to enhance pleasurable relaxation was associated with an increase in metabolic activity of the dorsal striatum (caudate, putamen) at session 2. These findings suggest that reversible changes in regional brain metabolic activity occur in conjunction with alterations in nicotine dependence. The results also highlight the likely role of thalamic gating processes as well as striatal reward and corticolimbic regulatory pathways in the maintenance of cigarette addiction.