18F-FDG Concentration Research Articles

Dosimetric Accuracy of Multi-Target Biology-Guided Radiotherapy Treatments in a Single Session

We present the first dosimetric measurements of single session, multi-target BgRT deliveries using a clinically realistic motion phantom on a research-only version of the RefleXion X1 system. A custom-made anthropomorphic phantom of a human torso with embedded fillable targets mimicking 18F-FDG-avid lesions was used. From the three embedded spherical targets, Target 1 was 26 mm in diameter coupled with a 3D independent respiratory motion with 22 mm range, whereas Target 2 and 3 were 22 mm in diameter and moved with a 1D 5 mm maximum sinusoidal motion. The 18F-FDG concentration in the background cavity of the phantom was 5 kBq/ml, and the targets were loaded with 10:1, 8:1 and 6:1 contrast relative to the background for Targets 1, 2, 3, respectively. Spherical structures were contoured as GTVs (CTV = GTV) and a 5 mm margin was added to create PTVs. Motion extent of the tumors were captured to create biological tracking zones for each target. Treatment plans were generated using a research version of the Reflexion treatment planning software to deliver 8 Gy/fx to the PTVs. The treatment delivery was repeated 2 times, and each time the phantom was refilled according to the plan. PET image evaluation metrics for each of the three targets were also recorded. Target dosimetry was measured using a combination of radiographic film and ion chamber. The maximum distance between the 97% prescription isodose line from the plan and the film measurements was used to characterize the dosimetric accuracy of the tracked deliveries. CTV and PTV min, max, and mean doses measured on film were also recorded for each target. Treatment plans were successfully created with 100% prescription dose coverage to each target loaded with different FDG ratios. Total treatment times for the single-plan, three-target deliveries were less than 80 minutes. PET evaluation metrics at imaging-only and pre-scan, and planning and film dosimetry to the GTV and PTV for each of the three targets is shown in table below (mean ± standard deviation of both deliveries). The CTV dose coverage was maintained for all targets. The shrinkage distance of the 97% prescription dose isodose line on the film plane for all three targets was less than 3 mm for both tests, and ranged from -0.4 to -2.34 mm. These results demonstrate that high tracking accuracy and dosimetric accuracy can be achieved in single session, multi-target deliveries over a range of target-to-background 18F-FDG concentrations and target motion patterns.

Evaluation of a High-Sensitivity Organ-Targeted PET Camera

The aim of this study is to evaluate the performance of the Radialis organ-targeted positron emission tomography (PET) Camera with standardized tests and through assessment of clinical-imaging results. Sensitivity, count-rate performance, and spatial resolution were evaluated according to the National Electrical Manufacturers Association (NEMA) NU-4 standards, with necessary modifications to accommodate the planar detector design. The detectability of small objects was shown with micro hotspot phantom images. The clinical performance of the camera was also demonstrated through breast cancer images acquired with varying injected doses of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (18F-FDG) and qualitatively compared with sample digital full-field mammography, magnetic resonance imaging (MRI), and whole-body (WB) PET images. Micro hotspot phantom sources were visualized down to 1.35 mm-diameter rods. Spatial resolution was calculated to be 2.3 ± 0.1 mm for the in-plane resolution and 6.8 ± 0.1 mm for the cross-plane resolution using maximum likelihood expectation maximization (MLEM) reconstruction. The system peak noise equivalent count rate was 17.8 kcps at a 18F-FDG concentration of 10.5 kBq/mL. System scatter fraction was 24%. The overall efficiency at the peak noise equivalent count rate was 5400 cps/MBq. The maximum axial sensitivity achieved was 3.5%, with an average system sensitivity of 2.4%. Selected results from clinical trials demonstrate capability of imaging lesions at the chest wall and identifying false-negative X-ray findings and false-positive MRI findings, even at up to a 10-fold dose reduction in comparison with standard 18F-FDG doses (i.e., at 37 MBq or 1 mCi). The evaluation of the organ-targeted Radialis PET Camera indicates that it is a promising technology for high-image-quality, low-dose PET imaging. High-efficiency radiotracer detection also opens an opportunity to reduce administered doses of radiopharmaceuticals and, therefore, patient exposure to radiation.

The expression of miRNA-216b is negatively correlated with 18F-FDG uptake in non-small cell lung cancer

BackgroundThis study aimed to investigate the correlation between miRNA-216b expression in patients with non-small cell lung cancer (NSCLC) and 18F-fluorodeoxyglucose (FDG) uptake by PET/CT and to explore the clinical application value of 18F-FDG PET/CT in miRNA-216b based on therapy for NSCLC.MethodsEighty patients with NSCLC and 40 healthy subjects were enrolled in our study. The SUVmax of the lesion area by PET/CT imaging was calculated. SUVmax represented the highest concentration of 18F-FDG in the lesion. The expression of miRNA-216b in the plasma and fiber bronchoscopic puncture of NSCLC patients was detected by RT qPCR. Then Pearson correlation analysis was used to analyze the correlation between miRNA-216b expression and 18F-FDG uptake in patients with different types of NSCLC.ResultsCompared with healthy subjects, SUVmax of early adenocarcinoma and advanced adenocarcinoma were increased. Compared with healthy subjects, SUVmax of early squamous and advanced squamous were increased. And the SUVmax content of advanced adenocarcinoma and squamous cell carcinoma was higher than that of early adenocarcinoma and squamous cell carcinoma. Compared with healthy subjects, the expression of miRNA-216b in the plasma of patients with early and advanced adenocarcinoma was reduced, and the expression of miRNA-216b in the plasma of patients with early and advanced squamous cell carcinoma was reduced. Compared with adjacent tissues, the expression of miRNA-216b in early adenocarcinoma tissues and advanced adenocarcinoma tissues was reduced, and the expression in early squamous cell carcinoma and advanced squamous cell carcinoma was reduced. Pearson correlation analysis showed a negative correlation between SUVmax and miRNA-216b (plasma and tissue) in patients with four types of NSCLC.ConclusionmiRNA-216b expression was negatively correlated with 18F-FDG uptake in NSCLC. miRNA-216b could be used for the classification and staging of non-small cell lung cancer. 18F-FDG PET/CT may be used to evaluate the therapeutic response in application of miRNA-216b-based cancer treatment.

Prognostic role of 18F-FDG PET-CT in the prone position in the evaluation of invasive breast carcinoma

Introduction: The objective of this study was to correlate the features of invasive breast carcinoma in 18F-FDG positron emission tomography/computed tomography with histopathological results, findings from other imaging methods, and survival. Methods: This observational single-center study included patients who underwent staging 18F-FDG positron emission tomography/ computed tomography between September 2012 and April 2019; the results were correlated with the findings of other imaging tests and anatomopathological results. Lesions were evaluated for their maximum standardized uptake value on positron emission tomography/computed tomography performed in the prone position. Tumors were classified into three subtypes (luminal, HER2 and triple-negative) based on immunohistochemical analyses. Results: A total of 125 patients with a mean age of 52 years (24–90 years) were analyzed. The primary tumor showed an increased 18F-FDG concentration on positron emission tomography/computed tomography in 122 (97.6%) patients, with a mean maximum standardized uptake value of 7.15 (1.0–32.9 range). The mean maximum standardized uptake value was higher in the triple-negative subtype (11.4; n=24) than in the luminal (6.2; n=89) and HER2 (5.0; n=9) subtypes (p<0.01). Tumors with more aggressive histological and immunohistochemical characteristics showed higher maximum standardized uptake values. Patients with a standardized uptake value greater than 7 in the primary tumor or greater than 6.7 in the axillary lymph nodes had poor overall survival (p=0.03 and p<0.01, respectively). Conclusions: Our study suggests that the maximum standardized uptake value obtained on positron emission tomography/computed tomography in the prone position may correlate with the tumor immunophenotype and overall survival regardless of the treatments performed, and can be used as a prognostic biomarker in invasive breast carcinoma patients.

18F-fluorodeoxyglucose positron emission tomography/computed tomography in the evaluation of spinal giant cell tumors

To investigate the value of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in the evaluation of spinal giant cell tumors (GCTs). The PET/CT and clinical data of 16 patients with spinal GCTs were reviewed. The maximal standardized uptake value (SUVmax), longest diameter, and CT features of spinal GCTs were analyzed. The value of PET/CT and MRI in displaying the recurrent lesions was compared. PET Response Criteria in Solid Tumors were adopted to evaluate the response to radiotherapy. Data from 7 males and 9 females (median age 32.5years) were analyzed. Eight patients had primary GCTs with a median SUVmax of 11.91 and a median length of 4.42cm. Eight patients had relapsed GCTs with a median SUVmax of 10.34 and a median length of 6.23cm. There was no statistical difference between the SUVmax of primary and relapsed GCTs. The SUVmax did not correlate with length. In 8 relapsed patients, 4 lesions invaded the vertebral canal, but 2 of which were not displayed on MRI. Metal prostheses showed extremely low signal intensity on MRI, even in the 3 cases with increased intra-prosthetic 18F-FDG concentration. Five relapsed patients with subsequent radiotherapy had a repeat PET/CT. A complete, partial, and stable metabolic response was observed in 1, 3, and 1 patient, respectively. Both the primary and recurrent spinal GCTs avidly accumulate 18F-FDG. For recurrent GCTs, PET/CT may provide incremental value in the assessment of the vertebral canal and intra-prosthetic involvement and the response to radiotherapy.

Abass Alavi: A giant in Nuclear Medicine turns 80 and is still going strong!

Abass Alavi: A giant in Nuclear Medicine turns 80 and is still going strong!

A novel 3D-printed phantom insert for 4D PET/CT imaging and simultaneous integrated boost radiotherapy.

To construct a 3D-printed phantom insert designed to mimic the variable PET tracer uptake seen in lung tumor volumes and a matching dosimetric insert to be used in simultaneous integrated boost (SIB) phantom studies, and to evaluate the design through end-to-end tests. A set of phantom inserts was designed and manufactured for a realistic representation of gated radiotherapy steps from 4D PET/CT scanning to dose delivery. A cylindrical phantom (φ80 × 120 mm) holds inserts for PET/CT scanning. The novel 3D printed insert dedicated to 4D PET/CT mimics high PET tracer uptake in the core and low uptake in the periphery. This insert is a variable density porous cylinder (φ44.5 × 70.0 mm), ABS-P430 thermoplastic, 3D printed by fused deposition modeling an inner (φ11 × 42 mm) cylindrical void. The square pores (1.8 × 1.8 mm2 each) fill 50% of outer volume, resulting in a 2:1 PET tracer concentration ratio in the void volume with respect to porous volume. A matching cylindrical phantom insert is dedicated to validate gated radiotherapy. It contains eight peripheral holes and one central hole, matching the location of the porous part and the void part of the 3D printed insert, respectively. These holes accommodate adaptors for Farmer-type ion chamber and cells vials. End-to-end tests were designed for imaging, planning, and dose measurements. End-to-end test were performed from 4D PET/CT scanning to transferring data to the planning system, target volume delineation, and dose measurements. 4D PET/CT scans were acquired of the phantom at different respiratory motion patterns and gating windows. A measured 2:1 18F-FDG concentration ratio between inner void and outer porous volume matched the 3D printed design. Measured dose in the dosimetric insert agreed well with planned dose on the imaging insert, within 3% for the static phantom and within 5% for most breathing patterns. The novel 3D printed phantom insert mimics variable PET tracer uptake typical of tumors. Obtained 4D PET/CT scans are suitable for segmentation and treatment planning and delivery in SIB gated treatments. Our experiments demonstrate the feasibility of this set of phantom inserts serving as end-to-end quality-assurance phantoms of SIB radiotherapy.

Estimation of kidneys and urinary bladder doses based on the region of interest in 18fluorine-fluorodeoxyglucose positron emission tomography/computed tomography examination: a preliminary study

Kidneys and urinary bladder are common physiologic uptake sites of 18fluorine-fluorodeoxyglucose (18F-FDG) causing increased exposure of low energy ionizing radiation to these organs. Accurate measurement of organ dose is vital as 18F-FDG is directly exposed to the organs. Organ dose from 18F-FDG PET is calculated according to the injected 18F-FDG activity with the application of dose coefficients established by International Commission on Radiological Protection (ICRP). But this dose calculation technique is not directly measured from these organs; rather it is calculated based on total injected activity of radiotracer prior to scanning. This study estimated the 18F-FDG dose to the kidneys and urinary bladder in whole body positron emission tomography/computed tomography (PET/CT) examination by comparing dose from total injected activity of 18F-FDG (calculated dose) and dose from organs activity based on the region of interest (ROI) (measured dose). Nine subjects were injected intravenously with the mean 18F-FDG dose of 292.42 MBq prior to whole body PET/CT scanning. Kidneys and urinary bladder doses were estimated by using two approaches which are the total injected activity of 18F-FDG and organs activity concentration of 18F-FDG based on drawn ROI with the application of recommended dose coefficients for 18F-FDG described in the ICRP 80 and ICRP 106. The mean percentage difference between calculated dose and measured dose ranged from 98.95% to 99.29% for the kidneys based on ICRP 80 and 98.96% to 99.32% based on ICRP 106. Whilst, the mean percentage difference between calculated dose and measured dose was 97.08% and 97.27% for urinary bladder based on ICRP 80 while 96.99% and 97.28% based on ICRP 106. Whereas, the range of mean percentage difference between calculated and measured organ doses derived from ICRP 106 and ICRP 80 for kidney doses were from 17.00% to 40.00% and for urinary bladder dose was 18.46% to 18.75%. There is a significant difference between calculated dose and measured dose. The use of organ activity estimation based on drawn ROI and the latest version of ICRP 106 dose coefficient should be explored deeper to obtain accurate radiation dose to patients.

Metal Artifact Reduction of CT Scans to Improve PET/CT.

In recent years, different metal artifact reduction methods have been developed for CT. These methods have only recently been introduced for PET/CT even though they could be beneficial for interpretation, segmentation, and quantification of the PET/CT images. In this study, phantom and patient scans were analyzed visually and quantitatively to measure the effect on PET images of iterative metal artifact reduction (iMAR) of CT data. Methods: The phantom consisted of 2 types of hip prostheses in a solution of 18F-FDG and water. 18F-FDG PET/CT scans of 14 patients with metal implants (either dental implants, hip prostheses, shoulder prostheses, or pedicle screws) and 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) PET/CT scans of 7 patients with hip prostheses were scored by 2 experienced nuclear medicine physicians to analyze clinical relevance. For all patients, a lesion was located in the field of view of the metal implant. Phantom and patients were scanned in a PET/CT scanner. The standard low-dose CT scans were processed with the iMAR algorithm. The PET data were reconstructed using attenuation correction provided by both standard CT and iMAR-processed CT. Results: For the phantom scans, cold artifacts were visible on the PET image. There was a 30% deficit in 18F-FDG concentration, which was restored by iMAR processing, indicating that metal artifacts on CT images induce quantification errors in PET data. The iMAR algorithm was useful for most patients. When iMAR was used, the confidence in interpretation increased or stayed the same, with an average improvement of 28% ± 20% (scored on a scale of 0%-100% confidence). The SUV increase or decrease depended on the type of metal artifact. The mean difference in absolute values of SUVmean of the lesions was 3.5% ± 3.3%. Conclusion: The iMAR algorithm increases the confidence of the interpretation of the PET/CT scan and influences the SUV. The added value of iMAR depends on the indication for the PET/CT scan, location and size/type of the prosthesis, and location and extent of the disease.

Development of a removable head fixation device for longitudinal behavioral and imaging studies in rats

BackgroundIn some behavioral neuroscience studies, an attachment is surgically fixed onto the head of an awake animal to allow the animal to perform learning tasks repeatedly in the same position in a task-training system. A recently developed task-training system enables operant conditioning of head-fixed rats within only a few days, and this system has been rigorously applied to record learning-associated neural activity using electrophysiological techniques. However, the head attachment of this device is made of metal and thus is not suitable for simultaneous brain imaging studies with X-ray computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography (PET). New methodWe developed a novel head fixation device with a removable attachment to position the rat head precisely in both imaging and training devices across different sessions. The device consisted of a removable attachment, a clamp and a stage, all of which were made of PET/MRI compatible acrylic resin. We tested the usefulness of the device with 18F-fluorodeoxyglucose (FDG) PET and CT. ResultsThe new device did not substantially affect 18F-FDG PET images. Repositioning of the rat's head across sessions and experimenters was at a level of submillimeter accuracy. Comparison with existing methodThe errors of radioactivity concentration of 18F-FDG in the PET image were lower with the present attachment than with the conventional metal attachment. Repositioning accuracy was considerably improved compared with a visual inspection method. ConclusionsThe developed fixation device is useful for longitudinal behavioral and brain imaging studies in rats.

Sphenoid Wing Meningioma Behavior on 11C-PiB and 18F-FDG PET

Two patients with mild cognitive impairment underwent C-PiB and F-FDG brain PET. Both patients had previously gone through a contrast-enhanced MRI scan that revealed extra-axial tumors next to the sphenoid wing, suggestive of meningiomas. C-PiB PET images showed a highly increased uptake by the extra-axial masses. These 2 cases represent 1.2% of our C-PiB population (n = 163). No meningioma was found with negative C-PiB uptake. The F-FDG concentration was not increased within the lesions. C-PiB could be used as a meningioma marker.

Can 18F-FDG PET improve the evaluation of suspicious breast lesions on MRI?

ObjectiveTo evaluate the impact of adding 18F-fluorine-2-deoxy-d-glucose (FDG) positron emission tomography (PET) in the evaluation of suspicious breast lesions on magnetic resonance imaging (MRI). MethodsSixty patients with suspicious breast lesions on MRI were selected to perform a PET–CT in prone position, dedicated to the evaluation of the breasts. The areas with increased 18F-FDG concentration relative to normal parenchyma were considered positive on PET–CT. Fusion of PET and MRI images (PET–MRI) was performed on a dedicated workstation to better locate corresponding lesions, and its findings were compared with histological results. Results76 lesions were evaluated, including 64 mass lesions (84.2%) and 12 non-mass lesions (15.8%). Lesions’ mean diameter on MRI was 29.6±19.2mm (range 6–94mm). PET–CT showed increased metabolically activity on 57 lesions (75.0%), with mean maximum SUV of 5.7±5.0 (range 0.8–23.1). On histopathology, there were 17 (22.4%) benign and 59 (79.7%) malignant lesions. Considering all lesions, PET–MRI fusion provided 89.8% sensitivity, 76.5% specificity and 86.8% accuracy. Considering only mass lesions higher than 10mm, PET–MRI fusion provided 95.8% sensitivity, 83.3% specificity and 93.3% accuracy. ConclusionThe inclusion of 18F-FDG PET on the evaluation of suspicious breast lesions on MRI helped to differentiate benign from malignant breast lesions, especially for mass lesions with a diameter higher than 10mm.

Reply to the letter by A. S. Ravi Kumar et al. regarding “Detectability of colorectal neoplasia with FDG-PET/CT”

We analyzed positive predictive values (PPVs) of fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) for detecting colorectal neoplasia using our published data [1]. PPVs for any neoplasia ([5 mm) were 46 % in the proximal colon and 70 % in the distal colon. In addition, PPVs for larger neoplasia ([11 mm) were 38 % in the proximal colon and 59 % in the distal colon. Thus, our PPVs were different from those reported by other authors including Lee et al. [2]. Both sensitivity and PPVs were lower in the proximal colon than in the distal colon in our study. PET/CT is occasionally faulted for revealing intense metabolic activity at sites not considered to be related to the malignant process under study. This physiologic uptake in the gastrointestinal tract has been attributed to uptake by smooth muscles or excretion and intraluminal concentration of 18F-FDG [3]. However, the discrepancy in PPVs between Lee et al.’s study and ours could be largely attributed to study design. We interpreted PET/CT images of the patients who underwent both PET/CT and colonoscopy without knowledge of colonoscopy findings, whereas in Lee et al.’s study, colonoscopy was performed to confirm positive findings of PET/CT. Firstly, the anatomical complexity of the distal colon may be an important factor. In Lee’s method, when positive 18F-FDG incorporation was observed in the proximal colon, colonoscopy was performed with the aim of discovering any lesion in the proximal colon. Then because of the anatomical complexity of the distal colon, neoplastic lesions, if present, in the distal colon may easily be missed. On the other hand, colonoscopists in our study were blinded to the results of PET/CT. Therefore, meticulous observation was performed throughout the colorectum because target lesions had not been known prior to colonoscopy. Thus, the aim of colonoscopy may have yielded a difference between the studies. Secondly, the difference in prevalence of neoplastic lesions may also be involved. As is well known, the prevalence of neoplastic lesions is higher in the distal colon than in the proximal colon. It is natural that unbiased interpretation of PET/CT yields a higher false-positive rate at the location where neoplastic lesions are sparser. Lastly, the state of mind of the interpreters of PET/CT images should be noted. In our study, interpreters were likely to overestimate the positivity of PET/CT. A false positive would be better than a false negative, because the latter call would suggest the interpreters were incompetent. In fact, in our study, the SUV max was likely to be lower in the false-positive cases than in the true-positive cases. In contrast, in Lee’s study, interpreters would have been likely to underestimate the positivity of PET/CT. A false negative would be better than a false positive in this This author’s reply refers to the letter to the editor at doi:10.1007s00535-012-0593-0.

Relapsing polychondritis detected in PET/CT

We report a case of relapsing polychondritis (RP) in a patient in whom PET/CT using 18F-FDG performed due to a suspicion of malignancy led to the diagnosis of RP. A previously healthy man, aged 57 years, was admitted to hospital for the diagnosis of chronic fever and weight loss of about 5 kg. Extensive laboratory and imaging evaluation showed only elevated C-reactive protein levels up to 180 mg/l (normal value <10 mg/l) and erythrocyte sedimentation rate up to 118 mm/h. Endoscopic evaluation showed signs of chronic laryngitis and sinusitis, oesophageal candidiasis, chronic gastritis and a benign sigmoid polyp. Antibacterial and antifungal therapy did not cause any significant improvement in the fever or laboratory findings. PET/CT using 18F-FDG showed diffuse 18F-FDG accumulation in all costal cartilages and in the sternal angle (SUVmax = 4.5). Additionally, symmetrically increased 18F-FDG activity in the joints of the upper extremities (elbows and wrists) was found. A moderately increased 18F-FDG concentration in the hypopharynx was also visible. The CT scan demonstrated thickened tracheal mucosa that did not show any 18F-FDG activity. The characteristic complex of signs and symptoms after exclusion of malignancy led to the diagnosis of RP – a rare autoimmune disease characterized by inflammation of cartilaginous tissues of the larynx, trachea and ears [1–3]. The patient was treated with glucocorticosteroids that provided rapid improvement of the symptoms and laboratory parameters.

Effective Radiotherapy of Primary Tumors and Metastasis with18F-2-Deoxy-2-Fluoro-D-Glucose in C57BL/6 Mice

The radiochemical 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG), a positron emitter, is taken up preferentially by malignant tumors with high metabolic rates. This concentration of 18F-FDG in the tumor permits diagnosis and staging by positron emission tomography but also may represent a means of targeting radiotherapy. In this study, we determined the effect of a higher dose of 18F-FDG on tumor growth in a mouse model. The effect of 18F-FDG on the growth and viability of 3 tumor cell lines was determined in vitro. Primary tumor growth and metastasis of B16/BL6 melanoma cells were determined in C57BL/6 mice injected with 5 mCi doses of 18F-FDG (2/3 doses). 18F-FDG was cytostatic for all 3 cell lines at the lowest dose tested. It significantly reduced the growth of primary tumors, by 89% at day 19 postinoculation, and also almost totally inhibited the appearance of lung metastases after intravenous inoculation of the same cells. 18F-FDG proved to be an effective radiotherapeutic agent in this model. The possible problems associated with the accumulation of this radiochemical at other sites besides the tumor must be addressed.

三次元｀１８´Ｆ‐ＦＤＧ ＰＥＴ／ＣＴ収集におけるオーバーラップ数の検討

The purpose of this study was to determine the best bed overlaps in PET/CT 3D acquisition to reconstruct a transverse image with uniform quality not depending on axial slice position. First, the value of the image contrast ratio, non-uniformity (NU) value, and coefficient of variation (COV) were examined in the image of a cylindrical phantom at each slice position. The image-contrast ratio was almost constant in all slice images, and the NU value and COV were also constant in the slice images up to 13 and 19 slices from the center, respectively, but these values increased with closeness to the edge of the detector. Secondly, COV and image contrast ratios at different sizes of (18)F-FDG concentration (phi 19 mm, phi 16 mm, phi 13 mm, phi 10 mm) were examined in the case of overlapping the bed frame with 11, 15, and 21 slices in acquiring data in 3D mode. In 21 and 15 slices overlapping in acquisition, the image contrast ratios for all concentrations were greater than 0.13, which was the threshold image contrast ratio needed to identify FDG concentration from the background image with naked eye scanning under our conditions. However, in 11 slices with overlapping acquisition, the image-contrast ratio for a phi 10 mm concentration were close to or less than 0.13 in the all slice images. As a result, 15 overlapping slices was a reasonable minimum number of slices to identify a phi 10 mm (18)F-FDG concentration while maintaining the image quality in PET/CT 3D acquisition in our institution.

Effects of anesthesia upon18F-FDG uptake in rhesus monkey brains

The kinetics of 18F-fluorodeoxyglucose (18F-FDG) in the monkey brain were monitored, and comparisons were made between the conscious state and when under ketamine and pentobarbital anesthesia. Rhesus monkeys were intravenously injected with 18F-FDG and followed by 60 min of PET scanning. In the conscious state, the 18F-FDG concentration reached a plateau 5 min after intravenous injection. Under ketamine anesthesia, the 18F-FDG concentration gradually increased with time in all monitored regions. At 60 min after injection, the concentration in the striatum was about 3.2 times greater than that in the conscious state, and about 4.5 times greater in the cerebral cortex. Under pentobarbital anesthesia, the 18F-FDG concentration in the occipital cortex was slightly lower. These findings demonstrate that 18F-FDG concentration in the monkey brain is significantly affected by anesthesia. The results also imply the existence of a short-term regulation mechanism for hexokinase activity in intact monkey brain.