Computational simulation of the predicted dosimetric impact of adjuvant yttrium-90 PET/CT-guided percutaneous ablation following radioembolization.

BACKGROUND: 90Y PET/CT post-radioembolization imaging has demonstrated that the distribution of 90Y in a tumor can be non-uniform. Using computational modeling, we predicted the dosimetric impact of post-treatment 90Y PET/CT-guided percutaneous ablation of the portions of a tumor receiving the lowest absorbed dose. A cohort of fourteen patients with non-resectable liver cancer previously treated using 90Y radioembolization were included in this retrospective study. Each patient exhibited potentially under-treated areas of tumor following treatment based on quantitative 90Y PET/CT. 90Y PET/CT was used to guide electrode placement for simulated adjuvant radiofrequency ablation in areas of tumor receiving the lowest dose. The finite element method was used to solve Penne's bioheat transport equation, coupled with the Arrhenius thermal cell-death model to determine 3D thermal ablation zones. Tumor and unablated tumor absorbed-dose metrics (average dose, D50, D70, D90, V100) following ablation were compared, where D70 is the minimum dose to 70% of tumor and V100 is the fractional tumor volume receiving more than 100 Gy. RESULTS: Compared to radioembolization alone, 90Y radioembolization with adjuvant ablation was associated with predicted increases in all tumor dose metrics evaluated. The mean average absorbed dose increased by 11.2 ± 6.9 Gy. Increases in D50, D70, and D90 were 11.0 ± 6.9 Gy, 13.3 ± 10.9 Gy, and 11.8 ± 10.8 Gy, respectively. The mean increase in V100 was 7.2 ± 4.2%. All changes were statistically significant (P < 0.01). A negative correlation between pre-ablation tumor volume and D50, average dose, and V100 was identified (ρ < - 0.5, P < 0.05) suggesting that adjuvant radiofrequency ablation may be less beneficial to patients with large tumor burdens. CONCLUSIONS: This study has demonstrated that adjuvant 90Y PET/CT-guided radiofrequency ablation may improve tumor absorbed-dose metrics. These data may justify a prospective clinical trial to further evaluate this hybrid approach.

Bariatric Radioembolization: A Pilot Study on Technical Feasibility and Safety in a Porcine Model.

PURPOSE: To evaluate feasibility of left gastric artery (LGA) yttrium-90 ((90)Y) radioembolization as potential treatment for obesity in a porcine model. MATERIALS AND METHODS: This study included 8 young female pigs (12-13 weeks, 21.8-28.1 kg). Six animals received infusions of (90)Y resin microspheres (46.3-105.1 MBq) into the main LGA and the gastric artery arising from the splenic artery. Animal weight and serum ghrelin were measured before treatment and weekly thereafter. Animals were euthanized 69-74 days after treatment, and histologic analyses of mucosal integrity and ghrelin immunoreactive cell density were performed. RESULTS: Superficial mucosal ulcerations < 3.0 cm(2) were noted in 5 of 6 treated animals. Ghrelin immunoreactive cell density was significantly lower in treated versus untreated animals in the stomach fundus (13.5 vs 34.8, P < .05) and stomach body (11.2 vs 19.8, P < .05). Treated animals gained less weight than untreated animals over the study duration (40.2 kg ± 5.4 vs 54.7 kg ± 6.5, P = .053). Average fundic parietal area (165 cm(2) vs 282 cm(2), P = .067) and average stomach weight (297.2 g vs 397.0 g, P = .067) were decreased in treated versus untreated animals. Trichrome staining revealed significantly more fibrosis in treatment animals compared with control animals (13.0 vs 8.6, P < .05). No significant differences were identified in plasma ghrelin concentrations (P = .24). CONCLUSIONS: LGA (90)Y radioembolization is promising as a potential treatment for obesity. A larger preclinical study is needed to evaluate the safety and efficacy of this procedure further.

How Sensitive Is the Upper Gastrointestinal Tract to 90Y Radioembolization? A Histologic and Dosimetric Analysis in a Porcine Model.

In 90Y radioembolization, nontarget embolization to the stomach or small bowel can result in gastrointestinal injury, a rare but difficult to manage clinical complication. However, dosimetric thresholds for toxicity to these tissues from radioembolization have never been evaluated in a controlled setting. We performed an analysis of the effect of 90Y radioembolization in a porcine model at different absorbed-dose endpoints. METHODS: Six female pigs underwent transfemoral angiography and infusion of 90Y-resin microspheres into arteries supplying part of the gastric wall. Esophagogastroduodenoscopy was performed after 4 wk to assess interim gastrointestinal health. Animals were monitored for side effects for 9 wk after 90Y infusion, after which they were euthanized and their upper gastrointestinal tracts were excised for analysis. Histologic sections were used to map microsphere location, and a microdosimetric evaluation was performed to determine the absorbed-dose profile within the gastrointestinal wall. RESULTS: 90Y radioembolization dosages from 46.3 to 105.1 MBq were infused, resulting in average absorbed doses of between 35.5 and 91.9 Gy to the gastric wall. No animal exhibited any signs of pain or gastrointestinal distress through the duration of the study. Excised tissue showed 1-2 small (<3.0 cm2) healed or healing superficial gastric lesions in 5 of 6 animals. Histologic analysis demonstrated that lesion location was superficial to areas of abnormally high microsphere deposition. An analysis of microsphere deposition patterns within the gastrointestinal wall indicated a high preference for submucosal deposition. Dosimetric evaluation at the luminal mucosa performed on the basis of microscopic microsphere distribution confirmed that 90Y dosimetry techniques conventionally used in hepatic dosimetry provide a first-order estimate of absorbed dose. CONCLUSION: The upper gastrointestinal tract may be less sensitive to 90Y radioembolization than previously thought. Lack of charged-particle equilibrium at the luminal mucosa may contribute to decreased toxicity of 90Y radioembolization compared with external-beam radiation therapy in gastrointestinal tissue. Clinical examples of injury from 90Y nontarget embolization have likely resulted from relatively large 90Y activities being deposited in small tissue volumes, resulting in absorbed doses in excess of 100 Gy.

A Microdosimetric Analysis of Absorbed Dose to Tumor as a Function of Number of Microspheres per Unit Volume in 90Y Radioembolization.

UNLABELLED: Differences in maximum tolerable absorbed dose to normal liver between (90)Y radioembolization and external-beam radiation therapy have been explained by citing differences in absorbed-dose heterogeneity at the microscopic level. We investigated microscopic absorbed-dose heterogeneity in radioembolization as a function of the number of microspheres per unit volume in tumor. The goal was to determine what effect the number of microspheres may have, if any, on tumor control in (90)Y radioembolization. METHODS: (90)Y PET/CT data were combined with microscopic probability-density functions describing microsphere clustering to provide realistic simulation using Monte Carlo modeling on both a macroscopic and a microscopic level. A complete microdosimetric analysis using 100-µm voxels was performed on the basis of (90)Y PET/CT data from 19 tumors treated using radioembolization. Simulations were performed with average tumor microsphere-number densities from 200 to 70,000 spheres/mL. Monte Carlo simulations of each tumor and number density were repeated 20 times to establish SE. A 2-way balanced ANOVA was used to determine whether differences in microsphere-number density affected common tumor-dose metrics. RESULTS: Decreasing the microsphere-number density resulted in a decrease in D70, the minimum dose to 70% of the tumor. The slope of the dose-volume histogram also decreased with decreasing microsphere-number density in all tumors. Compared with a density of 50,000 spheres/mL, decreases in D70 were statistically significant below 20,000 spheres/mL. However, these differences are unlikely to have clinical significance until the density decreases to below 5,000 spheres/mL. Although D70 was decreased at a low microsphere-number density, one can compensate for decreases by an increase in the average tumor-absorbed dose, that is, by increasing the radioembolization treatment dose. CONCLUSION: Differences in microsphere-number density may have an effect on microscopic tumor absorbed-dose inhomogeneity. These results begin to explain differences in treatment planning strategies between glass and resin radioembolization devices.

The evolution of image-guided lumbosacral spine surgery.

Techniques and approaches of spinal fusion have considerably evolved since their first description in the early 1900s. The incorporation of pedicle screw constructs into lumbosacral spine surgery is among the most significant advances in the field, offering immediate stability and decreased rates of pseudarthrosis compared to previously described methods. However, early studies describing pedicle screw fixation and numerous studies thereafter have demonstrated clinically significant sequelae of inaccurate surgical fusion hardware placement. A number of image guidance systems have been developed to reduce morbidity from hardware malposition in increasingly complex spine surgeries. Advanced image guidance systems such as intraoperative stereotaxis improve the accuracy of pedicle screw placement using a variety of surgical approaches, however their clinical indications and clinical impact remain debated. Beginning with intraoperative fluoroscopy, this article describes the evolution of image guided lumbosacral spinal fusion, emphasizing two-dimensional (2D) and three-dimensional (3D) navigational methods.

Simulation-based educational curriculum for fluoroscopically guided lumbar puncture improves operator confidence and reduces patient dose.

RATIONALE AND OBJECTIVES: Fluoroscopically guided lumbar puncture (FGLP) is a commonly performed procedure with increased success rates relative to bedside technique. However, FGLP also exposes both patient and staff to ionizing radiation. The purpose of this study was to determine if the use of a simulation-based FGLP training program using an original, inexpensive lumbar spine phantom could improve operator confidence and efficiency, while also reducing patient dose. MATERIALS AND METHODS: A didactic and simulation-based FGLP curriculum was designed, including a 1-hour lecture and hands-on training with a lumbar spine phantom prototype developed at our institution. Six incoming post-graduate year 2 (PGY-2) radiology residents completed a short survey before taking the course, and each resident practiced 20 simulated FGLPs using the phantom before their first clinical procedure. Data from the 114 lumbar punctures (LPs) performed by the six trained residents (prospective cohort) were compared to data from 514 LPs performed by 17 residents who did not receive simulation-based training (retrospective cohort). Fluoroscopy time (FT), FGLP success rate, and indication were compared. RESULTS: There was a statistically significant reduction in average FT for the 114 procedures performed by the prospective study cohort compared to the 514 procedures performed by the retrospective cohort. This held true for all procedures in aggregate, LPs for myelography, and all procedures performed for a diagnostic indication. Aggregate FT for the prospective group (0.87 ± 0.68 minutes) was significantly lower compared to the retrospective group (1.09 ± 0.65 minutes) and resulted in a 25% reduction in average FT (P = .002). There was no statistically significant difference in the number of failed FGLPs between the two groups. CONCLUSIONS: Our simulation-based FGLP curriculum resulted in improved operator confidence and reduced FT. These changes suggest that resident procedure efficiency was improved, whereas patient dose was reduced. The FGLP training program was implemented by radiology residents and required a minimal investment of time and resources. The LP spine phantom used during training was inexpensive, durable, and effective. In addition, the phantom is compatible with multiple modalities including fluoroscopy, computed tomography, and ultrasound and could be easily adapted to other applications such as facet injections or joint arthrograms.

The impact of an antireflux catheter on target volume particulate distribution in liver-directed embolotherapy: a pilot study.

PURPOSE: To determine if there are differences in hepatic distribution of embolic particles following infusion with a standard end-hole catheter versus an antireflux microcatheter. MATERIALS AND METHODS: This prospective study included nine patients (age, 48-86 y) enrolled for treatment of hepatocellular carcinoma (n = 6), liver-dominant metastatic disease (n = 2), or intrahepatic cholangiocarcinoma (n = 1) with resin yttrium-90 ((90)Y) microspheres. Before (90)Y treatment, each patient received two same-day sequential lobar infusions of technetium 99m ((99m)Tc) macroaggregated albumin (MAA) via a conventional end-hole catheter and an antireflux microcatheter positioned at the same location. Differences in technetium 99m-MAA distribution within tumor and nontarget sites were evaluated by single-photon emission computed tomography (SPECT) on a qualitative and semiquantitative basis. The antireflux microcatheter was used for the ensuing (90)Y treatment, with posttreatment (90)Y positron emission tomography/computed tomography to assess distribution of (90)Y microspheres. RESULTS: Decreases in hepatic nontarget embolization were found in all patients when the antireflux catheter was used. These decreases ranged from a factor of 0.11 to a factor of 0.76 (mean, 0.42; σ = 0.19), representing a 24%-89% reduction. Increased tumor deposition was also noted in all patients, ranging from a factor of 1.33 to a factor of 1.90 (mean, 1.68; σ = 0.20), representing a relative increase of 33%-90%. Both findings were statistically significant (P < .05). CONCLUSIONS: Although this pilot study identified differences in the downstream distribution of embolic particles when the antireflux catheter was used, further investigation is needed to determine if these findings are reproducible in a larger patient cohort and, if so, whether they are associated with any clinical impact.

A robust and inexpensive phantom for fluoroscopically guided lumbar puncture training.

INTRODUCTION: This report describes the creation process for an inexpensive, durable, lumbar spine phantom for use in fluoroscopically guided lumbar puncture (LP) training. METHODS: The LP phantom prototype was made from a polyvinyl chloride lumbar spine model embedded in a translucent rectangular block of commercially available thermoplastic polymer gel. Radiology residents with limited previous experience performing LP used the phantom for 20 simulated procedures to gain confidence before starting patient procedures. The residents completed surveys detailing their experiences with the phantom. RESULTS: Quantitative evaluation of the phantom using fluoroscopy and computed tomography suggested good physical agreement with human anatomy. Six board-certified radiologists viewed the phantom under live fluoroscopy and indicated that the phantom represented human anatomy with sufficient accuracy. Furthermore, surveys from resident trainees indicated that the thermoplastic tissue substitute simulated the texture and resistance of human soft tissue reasonably well for the purposes of clinical training. The total material cost of the LP phantom prototype was approximately US $148.00. CONCLUSIONS: This novel spine phantom can be produced with relatively low cost when compared with similar commercially available products. The phantom offers reasonable visual and tactile agreement to human anatomy and may be useful for improving the confidence of physician trainees. The LP phantom is durable and can easily be repaired by reheating the polymer tissue substitute.

Improved Accuracy of Minimally Invasive Transpedicular Screw Placement in the Lumbar Spine With 3-Dimensional Stereotactic Image Guidance: A Comparative Meta-Analysis.

STUDY DESIGN: This study compares the accuracy rates of lumbar percutaneous pedicle screw placement (PPSP) using either 2-dimensional (2-D) fluoroscopic guidance or 3-dimensional (3-D) stereotactic navigation in the setting of minimally invasive spine surgery (MISS). This represents the largest single-operator study of its kind and first comprehensive review of 3-D stereotactic navigation in the setting of MISS. OBJECTIVE: To examine differences in accuracy of lumbar pedicle screw placement using 2-D fluoroscopic navigation and 3-D stereotaxis in the setting of MISS. SUMMARY OF BACKGROUND DATA: Surgeons increasingly rely upon advanced image guidance systems to guide minimally invasive PPSP. Three-dimensional stereotactic navigation with intraoperative computed tomography offers well-documented benefit in open surgical approaches. However, the utility of 3-D stereotaxis in the setting of MISS remains incompletely explored by few studies with limited patient numbers. MATERIALS AND METHODS: A total of 599 consecutive patients underwent minimally invasive lumbar PPSP aided by 3-D stereotactic navigation. Postoperative imaging and medical records were analyzed for patient demographics, incidence and degree of pedicle breach, and other surgical complications. A total of 2132 screw were reviewed and compared with a meta-analysis created from published data regarding the placement of 4248 fluoroscopically navigated pedicle screws in the setting of MISS. RESULTS: In the 3-D navigation group, a total of 7 pedicle breaches occurred in 6 patients, corresponding to a per-person breach rate of 1.15% (6/518) and a per-screw breach rate of 0.33% (7/2132). Meta-analysis comprised of data from 10 independent studies showed overall breach risk of 13.1% when 2-D fluoroscopic navigation was utilized in MISS. This translates to a 99% decrease in odds of breach in the 3-D navigation technique versus the traditional 2-D-guided technique, with an odds ratio of 0.01, (95% confidence interval, 0.01-0.03), P<0.001. CONCLUSIONS: Three-dimensional stereotactic navigation based upon intraoperative computed tomography imaging offers markedly improved accuracy of percutaneous lumbar pedicle screw placement when used in the setting of MISS.

Reduction of patient anxiety in PET/CT imaging by improving communication between patient and technologist.

UNLABELLED: Patients experience anxiety during imaging procedures because of the confined space, uncertainty about the procedure, worry about the results, and other concerns. When a patient experiences anxiety during PET/CT imaging, the quality of the scan can be affected in several ways. Current patient-technologist communication is limited in PET/CT because the technologist must be separated from the patient during the course of the imaging workflow. This study investigated the use of a call device enabling rapid communication to reduce patient anxiety. METHODS: Clinical patients with various oncologic indications and undergoing (18)F-FDG PET/CT imaging were asked to participate in anxiety surveys under several conditions. Metrics were tracked regarding the survey results for comparison between groups and survey conditions. During the course of this study, 2 patient surveys were used. One of the patient populations was asked to fill out a survey on personal perceptions of the use of such a device, with questions related to their comfort with the device and the degree to which they perceived the device to reduce their anxiety. The 2 remaining populations were given a standard Spielberger State Anxiety survey for anxiety assessments against control populations. RESULTS: Perception survey results indicated that 75% of the respondents experienced a reduction in anxiety and that 84% would request this type of device for other procedures. A correlation was observed between improved patient-technologist communication and perceived feelings of safety, with identical percentages of positive responses. Although responses were mostly positive, 18.8% did not perceive any reduction in anxiety, and the same number indicated they would not use the system in the future. For those patients given the standard Spielberger State Anxiety survey, a statistically significant reduction in anxiety was observed (P < 0.05) in those patients given a call device. Reductions in anxiety were observed for all patient populations, including first-time and repeated-imaging patients. CONCLUSION: Patient anxiety can be reduced through the use of a tangible device that improves communication between the patient and the imaging staff. Reducing anxiety may have a positive effect on imaging, because involuntary motion may be reduced and there may be improvement in the patients' comfort and in their overall experience with the imaging procedure.

A Comparison of Techniques for (90)Y PET/CT Image-Based Dosimetry Following Radioembolization with Resin Microspheres.

(90)Y PET/CT following radioembolization has recently been established as a viable diagnostic tool, capable of producing images that are both quantitative and have superior image quality than alternative (90)Y imaging modalities. Because radioembolization is assumed to be a permanent implant, it is possible to convert quantitative (90)Y PET image sets into data representative of spatial committed absorbed-dose. Multiple authors have performed this transformation using dose-point kernel (DPK) convolution to account for the transport of the high-energy (90)Y ß-particles. This article explores a technique called the Local Deposition Method (LDM), an alternative to DPK convolution for (90)Y image-based dosimetry. The LDM assumes that the kinetic energy from each (90)Y ß-particle is deposited locally, within the voxel where the decay occurred. Using the combined analysis of phantoms scanned using (90)Y PET/CT and ideal mathematical phantoms, an accuracy comparison of DPK convolution and the LDM has been performed. Based on the presented analysis, DPK convolution provides no detectible accuracy benefit over the LDM for (90)Y PET-based dosimetry. For PET systems with (90)Y resolution poorer than 3.25 mm at full-width and half-max using a small voxel size, the LDM may produce a dosimetric solution that is more accurate than DPK convolution under ideal conditions; however, image noise can obscure some of the perceived benefit. As voxel size increases and resolution decreases, differences between the LDM and DPK convolution are reduced. The LDM method of post-radioembolization dosimetry has the advantage of not requiring additional post-processing. The provided conversion factors can be used to determine committed absorbed-dose using conventional PET image analysis tools. The LDM is a recommended option for routine post-radioembolization (90)Y dosimetry based on PET/CT imaging.

Radioembolization and the Dynamic Role of (90)Y PET/CT.

Before the advent of tomographic imaging, it was postulated that decay of (90) Y to the 0(+) excited state of (90)Zr may result in emission of a positron-electron pair. While the branching ratio for pair-production is small (~32 × 10(-6)), PET has been successfully used to image (90) Y in numerous recent patients and phantom studies. (90) Y PET imaging has been performed on a variety of PET/CT systems, with and without time-of-flight (TOF) and/or resolution recovery capabilities as well as on both bismuth-germanate and lutetium yttrium orthosilicate (LYSO)-based scanners. On all systems, resolution and contrast superior to bremsstrahlung SPECT has been reported. The intrinsic radioactivity present in LYSO-based PET scanners is a potential limitation associated with accurate quantification of (90) Y. However, intrinsic radioactivity has been shown to have a negligible effect at the high activity concentrations common in (90) Y radioembolization. Accurate quantification is possible on a variety of PET scanner models, with or without TOF, although TOF improves accuracy at lower activity concentrations. Quantitative (90) Y PET images can be transformed into 3-dimensional (3D) maps of absorbed dose based on the premise that the (90) Y activity distribution does not change after infusion. This transformation has been accomplished in several ways, although the most common is with the use of 3D dose-point-kernel convolution. From a clinical standpoint, (90) Y PET provides a superior post-infusion evaluation of treatment technical success owing to its improved resolution. Absorbed dose maps generated from quantitative PET data can be used to predict treatment efficacy and manage patient follow-up. For patients who receive multiple treatments, this information can also be used to provide patient-specific treatment-planning for successive therapies, potentially improving response. The broad utilization of (90) Y PET has the potential to provide a wealth of dose-response information, which may lead to development of improved radioembolization treatment-planning models in the future.

Intraprocedural yttrium-90 positron emission tomography/CT for treatment optimization of yttrium-90 radioembolization.

Radioembolization with yttrium-90 ((90)Y) microspheres relies on delivery of appropriate treatment activity to ensure patient safety and optimize treatment efficacy. We report a case in which (90)Y positron emission tomography (PET)/computed tomography (CT) was performed to optimize treatment planning during a same-day, three-part treatment session. This treatment consisted of (i) an initial (90)Y infusion with a dosage determined using an empiric treatment planning model, (ii) quantitative (90)Y PET/CT imaging, and (iii) a secondary infusion with treatment planning based on quantitative imaging data with the goal of delivering a specific total tumor absorbed dose.

Role of positron emission tomography/computed tomography in breast cancer.

Although positron emission tomography (PET) imaging may not be used in the diagnosis of breast cancer, the use of PET/computed tomography is imperative in all aspects of breast cancer staging, treatment, and follow-up. PET will continue to be relevant in personalized medicine because accurate tumor status will be even more critical during and after the transition from a generic metabolic agent to receptor imaging. Positron emission mammography is an imaging proposition that may have benefits in lower doses, but its use is limited without new radiopharmaceuticals.

Positron emission tomography/computed tomography in melanoma.

Fludeoxyglucose F 18 positron emission tomography/computed tomography (PET/CT) has been invaluable in the assessment of melanoma throughout the course of the disease. As with any modality, the studies are incomplete and more information will be gleaned as our experience progresses. Additionally, it is hoped that a newer PET agent in the pipeline will give us even greater success in the identification and subsequent treatment of melanoma. This article aims to examine the utilization of PET/CT in the staging, prognostication, and follow-up of melanoma while providing the physicians who order and interpret these studies practical guidelines and interpretive pitfalls.

Role of positron emission tomography/computed tomography in dementia.

This article provides a clinically based review of positron emission tomography (PET) imaging for dementia. Significant advances in nuclear medicine and molecular imaging techniques have improved the understanding of the genetic and molecular processes that define neurodegenerative dementia diseases. Metabolic imaging remains constant in its ability to document neuronal loss and lost function. Amyloid-ß radiotracers are useful in documenting amyloid deposition, differentiating origins of dementia and possibly predicting disease progression. These radiotracers may be useful in diagnosis-specific treatment. PET radiotracers have increased sensitivity and specificity to complement clinical presentation and other adjunct testing in the evaluation of dementia.

Limitations of dual time point PET in the assessment of lung nodules with low FDG avidity.

FDG PET has long shown efficacy in the evaluation of indeterminate pulmonary nodules. More recently, the use of dual time point imaging has been looked at as a means for improving sensitivity and accuracy. While initial reports were very promising, more recent results looking specifically at pulmonary lesions with low levels of FDG avidity demonstrated limitations. These lesions (initial maximum standard uptake value of less than 2.5) are of particular interest due to the fact that well-differentiated adenocarcinomas, broncheoaveolar carcinoma and carcinoid may have low FDG avidity on standard PET imaging, leading to false-negative exams. Our study retrospectively reviewed the accuracy of dual time point (DTP) FDG PET imaging to determine if it aided in the identification of malignant pulmonary nodules when initial time point imaging showed a maximum SUV of less than 2.5. 113 patients had undergone a total of 130 DTP PET/CT with 152 lesions assessed. 67 lesions were subsequently definitively diagnosed as benign or malignant based upon biopsy or imaging follow-up. Utilizing a maximum SUV increase of 10%, which optimizes our sensitivity and specificity; our results demonstrate a sensitivity of 63% and a specificity of 59%, similar to other investigators evaluating lesions with low FDG avidity. Increasing or decreasing this threshold did not improve our results, nor did the addition of lesions with maximum SUV's of 2.5 or greater on initial imaging. Specifically in nodules with low FDG avidity (max SUV<2.5), the sensitivity was 61%, specificity 58%, and accuracy was 60%. Our findings suggest that DTP FDG PET may not be of benefit in the assessment of pulmonary nodules with maximum SUV of less than 2.5 on initial imaging.

Normal organ standard uptake values in carbon-11 acetate PET imaging.

OBJECTIVE: The goal of this study was to determine normal standard uptake values of carbon-11 (11C) acetate in healthy organs. By accurately determining the range of physiologic activity, abnormal focal or diffuse 11C-acetate activity can be more accurately assessed and thus improve the sensitivity and specificity of this emerging diagnostic PET agent. METHODS: We reviewed all 55 patients (mean age+/-SD 64.8+/-10.8, age range 35-88 years) who underwent 11C-acetate PET/computed tomography at our institution from 2005 to 2007. Regions of interest were drawn in organs that were devoid of clinical or imaging evidence of disease. The maximum standard uptake value for each region was calculated and analyzed for mean, standard deviation, and 95% confidence intervals. RESULTS: The results are presented as average maximum standard uptake value+/-1 SD with the pancreas, liver, spleen and salivary glands showing the greatest 11C-acetate avidity. A review of the literature shows our results to be similar to those published earlier. CONCLUSION: Accurate knowledge of normal biodistribution and standardized uptake values will provide the foundation for assessing focal or diffuse organ disease while using this PET agent.

Comparison of planar scintigraphy alone and with SPECT for the initial evaluation of femoral neck stress fracture.

OBJECTIVE: The objective of our study was to compare the accuracy of planar scintigraphy alone versus planar scintigraphy with SPECT for the initial evaluation of femoral neck stress fractures in a young military population. MATERIALS AND METHODS: We retrospectively identified 38 patients who had undergone planar scintigraphy and 33 patients who had undergone planar scintigraphy and SPECT before MRI of the hips over a 6-month period for evaluation of suspected femoral neck fracture. Data were analyzed regarding the sensitivity and specificity of bone scanning alone and with SPECT for detecting femoral neck stress fracture and grading fractures as low grade (grades I and II) or high grade (grades III and IV). RESULTS: Twelve fractures were identified in the group who underwent planar scintigraphy alone and 13 in the group who underwent planar scintigraphy with SPECT. The sensitivities of planar scintigraphy alone and with SPECT were 50% and 92.3%, respectively (p = 0.03). The accuracy of each technique for the detection of high-grade fractures was 12.5% and 70%, respectively (p = 0.025). CONCLUSION: Planar scintigraphy with SPECT had a higher sensitivity and accuracy in assessing the grade of femoral neck stress fractures than planar scintigraphy alone. The results of this study suggest that SPECT should be performed with planar bone scintigraphy for the evaluation of patients with suspected femoral neck stress fractures.