A multicenter evaluation of commercial attenuation compensation techniques in cardiac SPECT using phantom models

BACKGROUND

Our goal was to evaluate the ability of current commercially available attenuation compensation (AC) techniques to correct for the effects of attenuation, scatter, and loss of resolution with depth, in a series of standardized phantom experiments.

METHODS AND RESULTS

The following systems were evaluated: Hawkeye (GE Medical Systems), Profile (Siemens Medical Systems), Vantage Pro (ADAC Laboratories), TAC (SMV America), M-STEP (University of Michigan, Ann Arbor), TransAct (Elscint), Beacon (Marconi Systems), and PET Advance (GE Medical Systems). Studies were performed with the use of normal and ischemic myocardium in air and with technetium 99m or fluorine 18 in torso phantoms. There was considerable variation in the uniformity of short-axis slices and defect contrast for images acquired in air (no AC). AC improved the uniformity of activity throughout normal myocardium. A simulated hot liver resulted in severe artifacts and was only partially corrected by many systems. A high-quality attenuation map appears to be an important determinant of image quality. No system produced AC images of comparable quality to those obtained in the absence of scatter/attenuating media.

CONCLUSIONS

There are significant differences in the ability of commercial AC systems to reduce artifacts due to attenuation and scatter. These differences are partly the result of non-AC factors (collimation, orbit, etc). In general, systems that generated high-quality attenuation maps yielded the best results.

The solitary pulmonary nodule: a primer on differential diagnosis

Despite significant advances in noninvasive imaging techniques, management of the solitary pulmonary nodule (SPN) remains a challenge for chest physicians. Patients with SPNs are frequently asymptomatic, and the physical examination is seldom revealing. Accurate diagnosis is essential, because >50% of patients will require prompt disease-specific therapy. The complexity of the problem is best appreciated by reviewing the differential list, which includes nearly 80 distinct clinical entities. Consequently, a thorough understanding of the more common etiologies is necessary to adequately treat patients with SPNs.

Positron emission tomography: measurement of the activity of second messenger systems

Phosphoinositide turnover is closely connected to modulation of synaptic function and is part of an important second messenger-producing system. New radioligands for imaging second messenger systems by positron emission tomography have been developed: carbon-11-labeled 1,2-diacylglycerols. The theoretical background of second messenger imaging is described in detail and the relation between the biologically active compounds and potential tracers for imaging second messenger systems is discussed. We report informative findings on postsynaptic biological responses in the living human brain of healthy normal subjects and with various diseases.

Comparison of spatial normalization procedures and their impact on functional maps

The alignment accuracy and impact on functional maps of four spatial normalization procedures have been compared using a set of high resolution brain MRIs and functional PET volumes acquired in 20 subjects. Simple affine (AFF), fifth order polynomial warp (WRP), discrete cosine basis functions (SPM), and a movement model based on full multi grid (FMG) approaches were applied on the same dataset for warping individual volumes onto the Human Brain Atlas (HBA) template. Intersubject averaged structural volumes and tissue probability maps were compared across normalization methods and to the standard brain. Thanks to the large number of degrees of freedom of the technique, FMG was found to provide enhanced alignment accuracy as compared to the other three methods, both for the grey and white matter tissues; WRP and SPM exhibited very similar performances whereas AFF had the lowest registration accuracy. SPM, however, was found to perform better than the other methods for the intra-cerebral cerebrospinal fluid (mainly in the ventricular compartments). Limited differences in terms of activation morphology and detection sensitivity were found between low resolution functional maps (FWHM approximately 10 mm) spatially normalized with the four methods, which overlapped in 42.8% of the total activation volume. These findings suggest that the functional variability is much larger than the anatomical one and that precise alignment of anatomical features has low influence on the resulting intersubject functional maps. When increasing the spatial resolution to approximately 6 mm, however, differences in localization of activated areas appear as a consequence of the different spatial normalization procedure used, restricting the overlap of the normalized activated volumes to only 6.2%.

Modeling [18 F]MPPF positron emission tomography kinetics for the determination of 5-hydroxytryptamine(1A) receptor concentration with multiinjection

The selectivity of [18F]MPPF (fluorine-18-labeled 4-(2;-methoxyphenyl)-1-[2;-(N-2"-pirydynyl)-p-fluorobenzamido]ethylpiperazine) for serotonergic 5-hydroxytryptamine(1A) (5-HT1A) receptors has been established in animals and humans. The authors quantified the parameters of ligand-receptor exchanges using a double-injection protocol. After injection of a tracer and a coinjection dose of [18F]MPPF, dynamic positron emission tomography (PET) data were acquired during a 160-minute session in five healthy males. These PET and magnetic resonance imaging data were coregistered for anatomical identification. A three-compartment model was used to determine six parameters: Fv (vascular fraction), K1, k2 (plasma/free compartment exchange rate), koff, kon/Vr (association and dissociation rate), Bmax (receptor concentration), and to deduce Kd (apparent equilibrium dissociation rate). The model was fitted with regional PET kinetics and arterial input function corrected for metabolites. Analytical distribution volume and binding potential were compared with indices generated by Logan-Patlak graphical analysis. The 5HT1A specificity for MPPF was evidenced. A Bmax of 2.9 pmol/mL and a Kd of 2.8 nmol/L were found in hippocampal regions, Kd and distribution volume in the free compartment were regionally stable, and the Logan binding potential was linearly correlated to Bmax. This study confirms the value of MPPF in the investigation of normal and pathologic systems involving the limbic network and 5-HT1A receptors. Standard values can be used for the simulation of simplified protocols.

[The PET scan in neuro-oncology--indications, differential diagnosis and clinical application]

Results of 157 PET (positron emission tomography) studies in 102 patients with known or presumed intracranial (ic.) tumors are reviewed. In 106 studies [18F]-2-fluoro-2-deoxy-D-glucose (FDG) and in 51 cases [11C]-methionine (MET) was used as the PET tracer. CT and MRI imaging accompanied the PET studies in each case. Results of pre- and/or postoperative studies are compared. PET was concluded to have a fundamental role in the precise differential diagnosis in case of ic. space-occupying pathologies since it is capable of providing information that is not obtainable or may be equivocal based solely on CT and/or MRI investigations. However, it is also mandatory to be aware of the limits of PET.

[Spatial standardization of [15O]-butanol PET images using T1-weighted MRI data]

Population averaged brain activation studies require the spatial standardization of the individual perfusion PET images. This procedure is usually supported by T1-weighted MRI images. The authors developed a segmentation technique to improve the automatized transformation of the individual MRI images into Talairach space. It was for the first time in Hungary that population averages of standardized T1-weighted MRI and [15O]-butanol PET images of the brain were created after validation of the procedure using data from 23 healthy volunteers. The newly developed method offers a solution for the automatized processing of primary data from brain activation experiments prior to statistical analysis.

[Clinical application of positron emission tomography (PET)]

Functional imaging using PET (positron emission tomography) has a great impact on current medical practice. It allows to explore, in a very precise way, different processes such as tissue flow and metabolism. Fluor-deoxyglucose labeled with F18 fluorine represents glucose metabolism. Among its main applications are detection, staging, follow up and recurrence assessment of malignant tumors; myocardial viability detection in patients with myocardial infarction or ischemic cardiomyopathy, and evaluation of hyperactive epileptogenic foci in brain. The basis and clinical applications of PET tomography are reviewed especially oriented to its cost benefit relationship, change in patient management and diagnostic value of the most accepted oncological indications. Important economic resources may be saved with PET in this field, considering appropriate staging and recurrence detection, avoiding expensive therapeutic approaches in advanced disease.

[Reliability of a positron emission tomography system (CTI:PT931/04-12)]

PURPOSE

The maintenance data of a PET system (PT931/04-12 CTI Inc.) was analyzed to evaluate its reliability.

METHOD

We examined whether the initial performance for the system resolution and efficiency is kept. The reliability of the PET system was evaluated from the value of MTTF (mean time to failure) and MTBF (mean time between failures) for each part of the system obtained from the maintenance data for 13 years.

RESULTS

The initial performance was kept for the resolution, but the efficiency decreased to 72% of the initial value. The 83% of the troubles of the system was for detector block (DB) and DB control module (BC). The MTTF of DB and BC were 2,733 and 3,314 days, and the MTBF of DB and BC per detector ring were 38 and 114 days. The MTBF of the system was 23 days. We found seasonal dependence for the number of troubles of DB and BC. This means that the trouble may be related the humidity.

CONCLUSION

The reliability of the PET system strongly depends on the MTBF of DB and BC. The improvement in quality of these parts and optimization of the environment in operation may increase the reliability of the PET system. For the popularization of PET, it is effective to evaluate the reliability of the system and to show it to the users.

Cancer Research UK procedures in manufacture and toxicology of radiotracers intended for pre-phase I positron emission tomography studies in cancer patients

Radiolabelled compounds formulated for injection (radiopharmaceuticals), are increasingly being employed in drug development studies. These can be used in tracer amounts for either pharmacokinetic or pharmacodynamic studies. Such radiotracer studies can also be carried out early in man, even prior to conventional Phase I clinical testing. The aim of this document is to describe procedures for production and safety testing of oncology radiotracers developed for imaging by positron emission tomography in cancer patients. We propose strategies for overcoming the inability to produce compounds in sufficient quantities via the radiosynthetic routes for full chemical characterisation and toxicology testing including (i) independent confirmation as far as possible that the stable compound associated with the radiopharmaceutical is identical to the non-labelled compound, (ii) animal toxicity studies with > or = 10 times (typically 100 times) the intended tracer dose in humans scaled by body surface area, and (iii) patient monitoring during the radiotracer positron emission tomography clinical trial.

Positron emission tomography and sentinel lymph node dissection in breast cancer

Sentinel lymph node dissection (SLND) is emerging as the preferred method of axillary staging for breast cancer patients. To further the use of noninvasive techniques in breast cancer, positron emission tomography (PET) scans have been considered as an alternative axillary staging modality. In order to compare the 2 modalities, we studied 15 invasive breast cancer patients who had undergone a preoperative PET scan before sentinel lymphadenectomy. PET scans were compared to axillary pathology results, which were defined as the greatest diameter of nodal metastases. Primary tumor sizes ranged from 0.5 cm to 5.0 cm (median,1.5 cm) and all were ductal in origin except for 1 invasive lobular and 1 mucinous carcinoma. Ten women had completion axillary dissections. Sentinel lymph node dissection was successful in all patients with completion dissections and no false-negative results. Five patients had sentinel node metastases, but PET scans identified only 1 of these patients, resulting in 4 false-negative PET scans. Missed metastases ranged in size from a micrometastatic focus identified only by immunohistochemistry to a nodal tumor measuring 11 mm in diameter. In addition, 1 woman with a PET-positive axilla was tumor free by SLND and remains free of axillary recurrence 29 months postoperatively. Two women had mediastinal uptake by PET scanning and were found to be tumor free after computerized tomography. The results of this preliminary study suggest that PET scanning using current techniques can be used as an adjunct to SLND rather than as an alternative staging technique.

Cost-minimization analysis of alternative diagnostic approaches in a modeled patient with non-small cell lung cancer and subcarinal lymphadenopathy

OBJECTIVE

To evaluate the costs of alternative diagnostic evaluations of enlarged subcarinal lymph nodes (SLNs) in modeled patients with non-small cell lung cancer (NSCLC).

METHODS

A cost-minimization model was used to compare 5 diagnostic approaches in the evaluation of enlarged SLNs in modeled patients with NSCLC. Values for the test performance characteristics and prevalence of malignancy in patients with SLN were obtained from the medical literature. The target population was adult patients known or suspected to have NSCLC with SLNs with a short axis length of at least 10 mm on thoracic computed tomography (CT).

RESULTS

The lowest-cost diagnostic work-up was by initial evaluation with endoscopic ultrasonography-guided fine-needle aspiration (EUS FNA) biopsy ($11,490 per patient) compared with mediastinoscopy (with biopsy) ($13,658), transbronchial FNA biopsy ($11,963), CT-guided FNA biopsy ($13,027), and positron emission tomography ($12,887). The results were sensitive to rate of SLN metastases and EUS FNA sensitivity. The EUS FNA biopsy remained least costly if the probability of SLN metastases exceeded 24% or EUS FNA sensitivity was higher than 76%. Primary mediastinoscopy was the most economical if not.

CONCLUSIONS

Which testing strategy is least costly for SLN evaluation in a modeled patient with NSCLC may be determined by the pretest probability of nodal metastases. Use of EUS FNA biopsy minimizes the cost of diagnostic evaluation in most cases.

Guidelines for brain radionuclide imaging. Perfusion single photon computed tomography (SPECT) using Tc-99m radiopharmaceuticals and brain metabolism positron emission tomography (PET) using F-18 fluorodeoxyglucose. The Belgian Society for Nuclear Medicine

The purpose of these guidelines is to assist nuclear medicine practitioners in recommending, performing, interpreting, and reporting the results of brain perfusion SPECT studies using Tc-99m radiopharmaceuticals and brain metabolism PET studies using F-18 fluorodeoxyglucose (FDG). These guidelines have been adapted and extended from those produced by the Society of Nuclear Medicine (Juni et al., 1998) and the European Association of Nuclear Medicine by a Belgian group of experts in the field trained in neurology and/or nuclear medicine. Some indications are not universally approved (e.g. brain death), but largely supported by the literature. They have been included in these guidelines in order to provide recommendations and a standardised protocol.

Metabolic and electrophysiological validation of functional MRI

OBJECTIVES

Although functional MRI is widely used for preoperative planning and intraoperative neuronavigation, its accuracy to depict the site of neuronal activity is not exactly known. Experience with methods that may validate fMRI data and the results obtained when coregistering fMRI with different preoperative and intraoperative mapping modalities including metabolically based (18)F-fluorodeoxyglucose PET, electrophysiologcally based transcranial magnetic stimulation (TMS), and direct electrical cortical stimulation (DECS) are described.

METHODS

Fifty patients were included. PET was performed in 30, TMS in 10, and DECS in 41 patients. After coregistration using a frameless stereotactic system, results were grouped into overlapping (<1 cm distance), neighbouring (<2 cm), or contradictory (>2 cm).

RESULTS

Comparing fMRI with PET, 18 overlapping, seven neighbouring, and one contradictory result were obtained. In four patients no comparison was possible (because of motion artefacts, low signal to noise ratio, and unusual high tumour metabolism in PET). The comparison of TMS and fMRI showed seven overlapping and three neighbouring results. In three patients no DECS results could be obtained. Of the remaining 38 patients, fMRI hand motor tasks were compared with DECS results of the upper limb muscles in 36 patients, and fMRI foot motor tasks were compared with DECS results of the lower limb on 13 occasions. Of those 49 studies, overlapping results were obtained in 31 patients, and neighbouring in 14. On four occasions fMRI did not show functional information (because of motion artefacts and low signal to noise).

CONCLUSIONS

All validation techniques have intrinsic limitations that restrict their spatial resolution. However, of 50 investigated patients, there was only one in whom results contradictory to fMRI were obtained. Although it is not thought that fMRI can replace the intraoperatively updated functional information (DECS), it is concluded that fMRI is an important adjunct in the preoperative assessment of patients with tumours in the vicinity of the central region.

Effects of acetazolamide on cerebral blood flow, blood volume, and oxygen metabolism: a positron emission tomography study with healthy volunteers

To evaluate changes in cerebral hemodynamics and metabolism induced by acetazolamide in healthy subjects, positron emission tomography studies for measurement of cerebral perfusion and oxygen consumption were performed. Sixteen healthy volunteers underwent positron emission tomography studies with 15O-gas and water before and after intravenous administration of acetazolamide. Dynamic positron emission tomography data were acquired after bolus injection of H2[15O] and bolus inhalation of 15O2. Cerebral blood flow, metabolic rate of oxygen, and arterial-to-capillary blood volume images were calculated using the three-weighted integral method. The images of cerebral blood volume were calculated using the bolus inhalation technique of C[15O]. The scans for cerebral blood flow and volume and metabolic rate of oxygen after acetazolamide challenge were performed at 10, 20, and 30 minutes after drug injection. The parametric images obtained under the two conditions at baseline and after acetazolamide administration were compared. The global and regional values for cerebral blood flow and volume and arterial-to-capillary blood volume increased significantly after acetazolamide administration compared with the baseline condition, whereas no difference in metabolic rate of oxygen was observed. Acetazolamide-induced increases in both blood flow and volume in the normal brain occurred as a vasodilatory reaction of functioning vessels. The increase in arterial-to-capillary blood volume made the major contribution to the cerebral blood volume increase, indicating that the raise in cerebral blood flow during the acetazolamide challenge is closely related to arterial-to-capillary vasomotor responsiveness.

Detection of occult disease in breast cancer using fluorodeoxyglucose camera-based positron emission tomography

An isolated increase of blood tumor marker CA 15.3 in breast cancer is considered a sensitive indicator for occult metastatic disease but by itself is not sufficient for initiating therapeutic intervention. We investigated the potential of camera-based positron emission tomography (PET) imaging using [18F]-fluorodeoxyglucose (FDG) to detect clinically occult recurrences in 132 female patients (age, 35-69 years) treated for breast cancer, all presenting with an isolated increase in blood tumor marker CA 15.3 without any other evidence of metastatic disease. FDG results were correlated to pathology results or to a sequentially guided conventional imaging method. One hundred nineteen patients were eligible for correlations. Positive FDG scans were obtained for 106 patients, including 89 with a single lesion and 17 with 2 or more lesion. There were 92 true-positive and 14 false-positive cases, 10 of which became true positive within 1 year. Among the 13 negative cases, 7 were false negative and 6 were true negative. Camera-based PET using FDG has successfully identified clinically occult disease with an overall sensitivity of 93.6% and a positive predictive value of 96.2%. The smallest detected size was 6 mm for a lymph node metastasis (tumor to nontumor ratio, 4:2). FDG camera-based PET localized tumors in 85.7% of cases suspected for clinically occult metastatic disease on the basis of a significant increase in blood tumor marker. A positive FDG scan associated with an elevated CA 15.3 level is most consistent with metastatic relapse of breast cancer.

Positron emission tomography in pulmonary masses where tissue diagnosis is unhelpful or not possible

OBJECTIVE

To document the usefulness of positron emission tomography (PET) in diagnosing lung masses where tissue diagnosis is not possible or is unhelpful.

DESIGN

Cohort study (partly retrospective).

SETTING

Departments of positron emission tomography and diagnostic imaging of a tertiary referral dedicated cancer hospital in Melbourne.

PATIENTS

40 of 60 consecutive patients referred for evaluation of an indeterminate lung nodule or mass, comprising 15 in whom biopsy was not possible and 25 in whom biopsy had either failed or did not confirm malignancy or a specific benign diagnosis.

MAIN OUTCOME MEASURES

Accuracy of blinded reading of PET scans in determining whether the lung lesion is benign or malignant (final diagnosis established either through surgical biopsy or from long term clinical and imaging follow-up).

RESULTS

PET yielded 23 true positives, 13 true negatives, 3 false positives (2 tuberculosis, 1 sarcoidosis) and 1 false negative (an adenocarcinoma), giving a sensitivity of 96%, a specificity of 81%, a negative predictive value of 93%, and a positive predictive value of 88% (for malignancy).

CONCLUSIONS

For lung nodules where tissue diagnosis was not possible or was unhelpful, the negative predictive power of PET was sufficiently high to avoid open biopsy, and to follow such patients with serial surveillance. On the other hand, most lesions that were positive on PET were either malignant or required specific active management determined from histological characterisation. PET therefore contributed to improved patient management and has reduced the need for open thoracotomy.

Imaging human mesolimbic dopamine transmission with positron emission tomography: I. Accuracy and precision of D(2) receptor parameter measurements in ventral striatum

Dopamine transmission in the ventral striatum (VST), a structure which includes the nucleus accumbens, ventral caudate, and ventral putamen, plays a critical role in the pathophysiology of psychotic states and in the reinforcing effects of virtually all drugs of abuse. The aim of this study was to assess the accuracy and precision of measurements of D(2) receptor availability in the VST obtained with positron emission tomography on the high-resolution ECAT EXACT HR+ scanner (Siemens Medical Systems, Knoxville, TN, U.S.A.). A method was developed for identification of the boundaries of the VST on coregistered high-resolution magnetic resonance imaging scans. Specific-to-nonspecific partition coefficient (V(3)") and binding potential (BP) of [(11)C]raclopride were measured twice in 10 subjects, using the bolus plus constant infusion method. [(11)C]Raclopride V(3)" in the VST (1.86 +/- 0.29) was significantly lower than in the dorsal caudate (DCA, 2.33 +/- 0.28) and dorsal putamen (DPU, 2.99 +/- 0.26), an observation consistent with postmortem studies. The reproducibility of V(3)" and BP were appropriate and similar in VST (V(3)" test-retest variability of 8.2% +/- 6.2%, intraclass correlation coefficient = 0.83), DCA (7.7% +/- 5.1%, 0.77), DPU (6.0% +/- 4.1%, 0.71), and striatum as a whole (6.3% +/- 4.1%, 0.78). Partial volume effects analysis revealed that activities in the VST were significantly contaminated by counts spilling over from the adjacent DCA and DPU: 70% +/- 5% of the specific binding measured in the VST originated from D(2) receptors located in the VST, whereas 12% +/- 3% and 18% +/- 3% were contributed by D(2) receptors in the DCA and DPU, respectively. Thus, accuracy of D(2) receptor measurement is improved by correction for partial voluming effects. The demonstration of an appropriate accuracy and precision of D(2) receptor measurement with [(11)C]raclopride in the VST is the first critical step toward the use of this ligand in the study of synaptic dopamine transmission at D(2) receptors in the VST using endogenous competition techniques.

A comparison of MRI and PET scanning in surgically staged loco-regionally advanced cervical cancer: potential impact on treatment

The aim of this study was to assess whether positron emission tomography (PET) or magnetic resonance imaging (MRI) could obviate the need for surgical staging in patients with locally advanced cervical carcinoma being planned for radiotherapy (RT). Imaging findings were compared to surgical staging in 27 patients including three with recent resection of the primary tumor. Both PET and MRI visualized all 24 residual cervical tumors. Primary tumor volume, as measured by MRI scan, ranged from 1.25 cc to 140 cc. In 24 patients evaluable for pelvic nodal status, PET had sensitivity, specificity, and positive and negative predictive values of 83%, 92%, 91% and 85%, respectively, with 88% accuracy. MRI detected only six in 12 (50%) patients with confirmed pelvic nodal disease, all of which were also seen by CT and PET, with an overall accuracy of 75%. PET detected only four in seven (57%) cases with confirmed para-aortic (PA) involvement. All histologically confirmed sites not visualized on PET were <1 cm. Without surgical staging, six in 10 (60%) patients with histologically proven pelvic nodal disease would not have received pelvic boost if guided by MRI alone, compared to two in 10 (20%) patients guided by PET alone or in combination with MRI. All four patients with positive PA on PET were confirmed on histology or clinical follow-up, including one case that proved to be a false negative one on surgery. However, in three cases, PET would have yielded an inadequate radiation volume. In conclusion, the positive predictive value of PET in the pelvis and para-aortic region appears sufficient to obviate lymph nodal sampling, but sampling is still required to exclude small-volume disease cranial to sites of abnormality on PET. MRI has insufficient accuracy for nodal staging to impact management.