Three-dimensional PET emission scan registration and transmission scan synthesis

The duration of a positron emission tomography (PET) imaging scan can be reduced if the transmission scan of one patient which is used for emission correction can be synthesized by using the reference transmission scan of another patient. In this paper, we propose a new intersubjects PET emission scan registration method and PET transmission synthesis method by using the boundary information of the body or brain scan of the PET emission scans. The PET emission scans have poor image quality and different intensity statistics so that we preprocess the emission scans to have similar histogram and then apply the point distribution model (PDM) [15] to extract the contours of the emission scan. The extracted boundary contour of every slice is used to reconstruct the three-dimensional (3-D) surface of the reference set and the target set. Our registration is 3-D surface-based which uses the normal flow method [17] to find the correspondence vector field between two 3-D reconstructed surfaces. Since it is difficult to analyze internal organ using the PET emission scan imaging without correction, we assume that the deformation of internal organ is homogeneous. With the corresponding vector field between the two emission scans and the transmission scan of the reference set, we can synthesize the transmission scan of the target set.     

Model-based scatter correction for fully 3D PET

A method is presented that directly calculates the mean number of scattered coincidences in data acquired with fully 3D positron emission tomography (PET). This method uses a transmission scan, an emission scan, the physics of Compton scatter, and a mathematical model of the scanner in a forward calculation of the number of events for which one photon has undergone a single Compton interaction. The distribution of events for which multiple Compton interactions have occurred is modelled as a linear transformation of the single-scatter distribution. Computational efficiency is achieved by sampling at rates no higher than those required by the scatter distribution and by implementing the algorithm using look-up tables. Evaluation studies in phantoms with large scatter fractions show that the method yields images with quantitative accuracy equivalent to that of slice-collimated PET in clinically useful times.     

The design of an animal PET: flexible geometry for achieving optimal spatial resolution or high sensitivity

We present the design of a positron emission tomograph (PET) with flexible geometry dedicated to in vivo studies of small animals (TierPET). The scanner uses two pairs of detectors. Each detector consists of 400 small individual yttrium aluminum perovskite (YAP) scintillator crystals of dimensions 2 x 2 x 15 mm3, optically isolated and glued together, which are coupled to position-sensitive photomultiplier tubes (PSPMT's). The detector modules can be moved in a radial direction so that the detector-to-detector spacing can be varied. Special hardware has been built for coincidence detection, position detection, and real-time data acquisition, which is performed by a PC. The single-event data are transferred to workstations where the radioactivity distribution is reconstructed. The dimensions of the crystals and the detector layout are the result of extensive simulations which are described in this report, taking into account sensitivity, spatial resolution and additional parameters like parallax error or scatter effects. For the three-dimensional (3-D) reconstruction a genuine 3-D expectation-maximization (EM)-algorithm which can include the characteristics of the detector system has been implemented. The reconstruction software is flexible and matches the different detector configurations. The main advantage of the proposed animal PET scanner is its high flexibility, allowing the realization of various detector-system configurations. By changing the detector-to-detector spacing, the system is capable of either providing good spatial resolution or high sensitivity for dynamic studies of pharmacokinetics.     

Evaluation of exercise tolerance of patients with heart failure and its clinical significance

A new method of PET attenuation using post-injection transmission scan is presented, which is especially useful in 18F-FDG static studies. The transmission scan is acquired right before the emission scan, which is used to subtract the emission component from the transmission data. When the effect of measurement condition upon the image noise was evaluated with a 20 cm diameter cylindrical phantom, an increase in the injection dose inflated the noise and caused artifacts. There was an optimum dose that minimized the image noise. As the external source activity increased, the image noise decreased, and the optimum dose increased linearly, which enabled estimation of the optimum injection dose under a given external source. When the total (emission plus transmission) scan time was fixed, longer emission scan resulted in better images than longer transmission scan.     

Transfectable and transplantable postmitotic human neurons: a potential "platform" for gene therapy of nervous system diseases

OBJECTIVE: To evaluate F-18 fluorodeoxyglucose positron emission tomography (PET) in terms of its sensitivity and specificity in diagnosing malignant pulmonary nodules and staging bronchogenic carcinoma. METHODS: A retrospective review of any patient that presented to the VA Palo Alto Health Care System with a pulmonary nodule between 9/94 and 3/96 revealed 49 patients (four female, 45 male) age 37-85 (mean 63) with 54 pulmonary nodules who had: chest CT scan, PET scan; and tissue characterization of the nodule. Characterization of each nodule was achieved by histopathologic (N = 44) or cytopathologic (N = 10) analysis. Of the 49 patients, 18 had bronchogenic carcinoma which was adequately staged. Mediastinal PET and CT findings in these 18 patients were compared with the surgical pathology results. N2 disease was defined as mediastinal lymph node involvement by the American Thoracic Society's classification system. Mediastinal lymph nodes were interpreted as positive by CT if they were larger that 1.0 cm in the short-axis diameter. RESULTS: Sensitivity and specificity for the diagnosis of malignant pulmonary nodules using PET was 93 and 70%, respectively. All nodules (N = 3) that were falsely positive by PET scan were infectious in origin. All nodules (N = 4) that were falsely negative by PET were technically limited studies (outdated scanner, no attenuation correction, hyperglycemia) except for one case of metastatic adenocarcinoma. The sensitivity and specificity of PET in diagnosing N2 disease was 67 and 100%, compared with 56% and 100% for CT scan (not statistically significant). However, one more patient with N2 disease was correctly diagnosed by PET than by CT scan. CONCLUSION: PET is a valuable tool in the diagnosis and management of pulmonary nodules and may more accurately stage patients with bronchogenic carcinoma than CT scanning alone.     

Evaluation of the detectability of breast cancer lesions using a modified anthropomorphic phantom

During the development and characterization of imaging technology or new imaging protocols, it is usually instructive to perform phantom experiments. Often, very simplified forms of the realistic patient anatomy are used that may be acceptable under certain conditions; however, the implications for patient studies can be misleading. This is particularly true in breast and axillary node imaging. The complexities presented by the anatomy, variable object scatter, attenuation and inhomogeneous distribution of activity in this upper thoracic region provide a significant challenge to the imaging task. METHODS: A tissue-equivalent anthropomorphic phantom of the thorax (Radiology Support Devices, Inc., Long Beach, CA) containing fillable cavities and organs was modified for the studies. The phantom was filled with realistic levels of FDG activity and scanned on a Siemens ECAT HR+ whole-body PET scanner. Breast attachments containing 2.0- and 2.55-cc lesions with lesion-to-background ratios of 5:1 and 7:1, respectively, were imaged. Scatter and attenuation effects were analyzed with various experimental setups. A lymph node experiment and a multibed position whole-phantom scan also were performed to illustrate the extent to which the phantom represents the human thorax. RESULTS: Regions of interest were drawn on the lesions as well as the background breast tissue in all studies. It was found that the signal-to-noise ratio decreased 65% when a more realistic phantom (lesions plus breasts plus thorax, all containing activity) was used, as compared to a simple phantom (lesions plus breasts containing activity; no thorax), due to the effects of increased scatter and attenuation. A 23% decrease in the contrast also was seen from the scan of the more realistic phantom due to surrounding activity from nearby organs such as the heart, as well as an increase in the volume of attenuating media. CONCLUSION: This new phantom allows us to more realistically model the conditions for breast and lymph node imaging, leading to preclinical testing that will produce results that better approximate those that will be found in vivo. The phantom will be a valuable tool in comparing different imaging technologies, data collection strategies and image reconstruction algorithms for applications in breast cancer using PET, SPECT or scintimammography systems.     

Squamous intraepithelial lesions in young female university students]

Positron emission tomography and nuclear magnetic resonance spectroscopy are non-invasive techniques that allow serial metabolic measurements to be obtained in a single subject. Significant advantages could be obtained if both types of scans could be acquired with a single machine. A small-scale PET scanner, designed to operate in a high magnetic field, was therefore constructed and inserted into the top half of a 7.3 cm bore, 9.4 T NMR magnet and its performance characterized. The magnetic field did not significantly affect either the sensitivity (approximately 3 kcps/MBq) or the spatial resolution (2.0 mm full width at half maximum, measured using a 0.25 mm diameter line source) of the scanner. However, the presence of the PET scanner resulted in a small decrease in field homogeneity. The first, simultaneous 31P NMR spectra (200, 80 degrees pulses collected at 6 s intervals) and PET images (transverse, mid-ventricular slices at the level of the mitral value) from isolated, perfused rat hearts were acquired using a specially designed NMR probe inserted into the bottom half of the magnet. The PET images were of excellent quality, enabling the left ventricular wall and interventricular septum to be clearly seen. In conclusion, we have demonstrated the simultaneous acquisition of PET and NMR data from perfused rat hearts; we believe that the combination of these two powerful techniques has tremendous potential in both the laboratory and the clinic.     

Controlled prospective study of positron emission tomography using the glucose analogue [18f]fluorodeoxyglucose in the evaluation of pulmonary nodules

BACKGROUND: Positron emission tomography (PET) is a new imaging technique which, by measuring focal metabolic activities, can make a qualitative statement (benign or malignant) about a tumour. PET has been described in many studies to provide a high diagnostic accuracy for the evaluation of pulmonary coin lesions. However, these studies were not always supported by histological confirmation of the results. In a controlled prospective study, it was investigated whether the diagnostic accuracy of PET is sufficiently high to allow omission of diagnostic thoracotomy or thoracoscopy in the case of a negative finding. METHODS: A PET scan was carried out before operation using [18F]fluorodeoxyglucose (FDG) in 50 patients with pulmonary coin lesions (diameter 30 mm or less). All of these lesions were completely removed thoracoscopically or by a formal thoracotomy and were examined histologically. Using the histology results, the diagnostic accuracy of the PET procedure with regard to a benign or malignant diagnosis was evaluated and compared with that of computed tomography (CT). Results From a total of 54 coin lesions (four of the 50 patients had two lesions) there were 31 malignant (19 primary bronchial carcinomas, 12 metastases) and 23 benign diagnoses. With the PET procedure 28 of 31 malignant and 19 of 23 benign lesions were classified correctly (sensitivity 90 per cent, specificity 83 per cent). False negatives included two bronchial carcinomas and one metastasis. CT had a sensitivity of 100 per cent and specificity of 52 per cent. CONCLUSION: FDG PET cannot generally be considered as a replacement for diagnostic thoracoscopy or thoracotomy at the present time. However, by combining FDG PET with radiological follow-up, clinical applications may evolve in patients at low risk for a malignant tumour or at high risk for surgical complications.     

"Anatometabolic" tumor imaging: fusion of FDG PET with CT or MRI to localize foci of increased activity

Positron emission tomographic (PET) images of visceral cancers are commonly visualized as "hot spots" of increased activity with relatively little normal anatomy discernable, when 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) is used as the tracer. We describe a method by which computed tomography or magnetic resonance anatomic images can be digitally fused in three dimensions, using a rigid rotate-translate scale model with PET "metabolic" images, to simultaneously display registered anatomic and metabolic information. Such "anatometabolic" fusion images were produced in 10 patients with a variety of visceral cancers. External fiducial markers placed during both the anatomic and the metabolic study, as well as internal anatomic fiducials defined from landmarks observed on reconstructed transmission images, were used to achieve image fusion. The mean error magnitude +/- s.e.m. of fiducial registration in the nine patients with successful realignments was 5.0 +/- 0.8 mm. The mean accuracy in realignment between known anatomic structures seen on both the anatomic study and on the emission PET scan (but not used in realignment) was 6.3 +/- 0.8 mm. Localization of foci of increased FDG uptake to specific anatomic structures was achieved by this method, which represented an enhancement over the rudimentary anatomy available from the emission images alone. Anatometabolic fusion images made using this reasonably simple method should prove useful in the management of patients with cancer and other diseases.     

Performance evaluation of a whole-body PET scanner using the NEMA protocol. National Electrical Manufacturers Association

This study evaluates the performance of the newly developed high-resolution whole-body PET scanner ECAT EXACT HR+. METHODS: The scanner consists of four rings of 72 bismuth germanate block detectors each, covering an axial field of view of 15.5 cm with a patient port of 56.2 cm. A single block detector is divided into an 8 x 8 matrix, giving a total of 32 rings with 576 detectors each. The dimensions of a single detector element are 4.39 x 4.05 x 30 mm3. The scanner is equipped with extendable tungsten septa for two-dimensional two-dimensional measurements, as well as with three 68Ge line sources for transmission scans and daily quality control. The spatial resolution, scatter fraction, count rate, sensitivity, uniformity and accuracy of the implemented correction algorithms were evaluated after the National Electrical Manufacturers Association protocol using the standard acquisition parameters. RESULTS: The transaxial resolution in the two-dimensional mode is 4.3 mm (4.4 mm) in the center and increases to 4.7 mm (4.8 mm) tangential and to 8.3 mm (8.0 mm) radial at a distance of r = 20 cm from the center. The axial slice width measured in the two-dimensional mode varies between 4.2 and 6.6 mm FWHM over the transaxial field of view. In the three-dimensional mode the average axial resolution varies between 4.1 mm FWHM in the center and 7.8 mm at r = 20 cm. The scatter fraction is 17.1% (32.5%) for a lower energy discriminator level of 350 keV. The maximum true event count rate of 263 (345) kcps was measured at an activity concentration of 142 (26.9) kBq/ml. The total system sensitivity for true events is 5.7 (27.7) cps/Bq/ml. From the uniformity measurements, we obtained a volume variance of 3.9% (5.0%) and a system variance of 1.6% (1.7%). The implemented three-dimensional scatter correction algorithm reveals very favorable properties, whereas the three-dimensional attenuation correction yields slightly inaccurate results in low- and high-density regions. CONCLUSION: The ECAT EXACT HR+ has an excellent, nearly isotropic spatial resolution, which is advantageous for brain and small animal studies. While the relatively low slice sensitivity may hamper the capability for performing fast dynamic two-dimensional studies, the scanner offers a sufficient sensitivity and count rate capacity for fully three-dimensional whole-body imaging.     

Imaging of myocardial perfusion and metabolism with positron emission tomography

Positron emission tomography (PET) has been providing new information in the diagnosis and the pathophysiological assessment of heart diseases. The PET tracers commonly used in Japan are 13N-ammonia, 18F-fluorodeoxyglucose (FDG) for imaging of myocardial perfusion and metabolism, respectively. Measurement of regional myocardial blood flow by 13N-ammonia dynamic PET scan and a compartment model analysis is applied to the functional estimation of coronary stenotic lesions and the detection of perfusion abnormalities in hypertrophic heart diseases, familial hyperchlesterolemia and other diseases with possible microvascular lesions. 18F-FDG is commonly used to differentiate ischemic but viable tissue from myocardial scar in coronary artery disease and also used to detect cardiac tumor and the cardiac involvement in sarcoidosis. In addition to these two tracers, 11C-acetate is now expected to provide the clinical analysis of pathophysiology of heart failure by estimating the efficiency of energy conversion of the heart into external work.     

Transmission scanning in emission tomography

Attenuation correction in single-photon (SPET) and positron emission (PET) tomography is now accepted as a vital component for the production of artefact-free, quantitative data. The most accurate attenuation correction methods are based on measured transmission scans acquired before, during, or after the emission scan. Alternative methods use segmented images, assumed attenuation coefficients or consistency criteria to compensate for photon attenuation in reconstructed images. This review examines the methods of acquiring transmission scans in both SPET and PET and the manner in which these data are used. While attenuation correction gives an exact correction in PET, as opposed to an approximate one in SPET, the magnitude of the correction factors required in PET is far greater than in SPET. Transmission scans also have a number of other potential applications in emission tomography apart from attenuation correction, such as scatter correction, inter-study spatial co-registration and alignment, and motion detection and correction. The ability to acquire high-quality transmission data in a practical clinical protocol is now an essential part of the practice of nuclear medicine.     

Whole-body positron emission tomography in clinical oncology: comparison between attenuation-corrected and uncorrected images

The clinical need for attenuation correction of whole-body positron emission tomography (PET) images is controversial, especially because of the required increase in imaging time. In this study, regional tracer distribution in attenuation-corrected and uncorrected images was compared in order to delineate the potential advantages of attenuation correction for clinical application. An ECAT EXACT scanner and a protocol including five to seven bed positions, emission scans of 9 min and post-injection transmission scans of 10 min per bed position were used. Uncorrected and attenuation-corrected images were reconstructed by filtered backprojection. In total, 109 areas of focal fluorine-18 fluorodeoxyglucose (FDG) uptake in 34 patients undergoing PET for the staging of malignancies were analysed. To measure focus contrast, a ratio of focus (target) to background average countrates (t/b ratio) was obtained from transaxial slices using a region of interest technique. Calculation of focus diameters by a distance measurement tool and visual determination of focus borders were performed. In addition, images of a body phantom with spheres to simulate focal FDG uptake were acquired. Transmission scans with and without radioactivity in the phantom were used with increasing transmission scanning times (2-30 min). The t/b ratios of the spheres were calculated and compared for the different imaging protocols. In patients, the t/b ratio was significantly higher for uncorrected images than for attenuation-corrected images (5.0+/-3.6 vs 3.1+/-1.4; P<0.001). This effect was independent of focus localization, tissue type and distance to body surface. Compared with the attenuation-corrected images, foci in uncorrected images showed larger diameters in the anterior-posterior dimension (27+/-14 vs 23+/-12 mm; P<0.001) but smaller diameters in the left-right dimension (19+/-11 vs 21+/-11 mm; P<0.001). Phantom data confirmed higher contrast in uncorrected images compared with attenuation-corrected images. It is concluded that, although distortion of foci was demonstrated, uncorrected images provided higher contrast for focal FDG uptake independent of tumour localization. In most clinical situations, the main issue of whole-body PET is pure lesion detection with the highest contrast possible, and not quantification of tracer uptake. The present data suggest that attenuation correction may not be necessary for this purpose.     

A rotating PET scanner using BGO block detectors: design, performance and applications

Recent advances in fully three-dimensional reconstruction for multi-ring PET scanners have led us to explore the potential of a prototype scanner based on the rotation of two opposing arrays of BGO block detectors. The prototype contains only one-third of the number of detectors in the equivalent full ring scanner, resulting in reduced cost. With a lower energy threshold at 250 keV, the absolute efficiency of the scanner is 0.5% and the scatter fraction is 35% for a 20-cm cylinder. Transaxial and axial spatial resolution is about 6 mm. The maximum noise equivalent count rate estimated for a 15-cm diameter cylinder is 36,000 cps at a concentration of 26 kBq/ml. The minimum scan time for a 18F-fluoro-2-deoxyglucose (FDG) brain study is 55 sec. The camera has been validated for clinical applications using both FDG and 82Rb.     

Multiple line source array for SPECT transmission scans: simulation, phantom and patient studies

Accurate attenuation and scatter corrections in quantitative SPECT studies require attenuation maps of the density distribution in the scanned object. These can be obtained from simultaneous emission/transmission scans. METHODS: A new method has been developed using a multiple line source array (MLA) for transmission scans, and its performance has been investigated using computer simulations and experimental data. The activity in the central lines of the MLA was higher than at the edges of the system, so that more transmission photons would be directed toward the thicker parts of the human body. A series of transmission-only and simultaneous emission/transmission studies were performed for different phantom configurations and human subjects. Attenuation maps were generated and used in reconstruction of attenuation-corrected emission images. RESULTS: The mu coefficients for attenuation maps obtained using the MLA system and simulated and experimental data display no artifacts and are qualitatively and quantitatively correct. For phantoms, the agreement between the measured and the true value of mu for water was found to be better than 4%. The attenuation-corrected emission images for the phantom studies demonstrate that the activity in the heart can be accurately reconstructed. A significant qualitative improvement was also obtained when the attenuation correction was used on patient data. CONCLUSION: Our results indicate that the MLA transmission source can be used in simultaneous transmission/emission imaging to generate accurate attenuation maps. These maps allow for performing an object-specific, attenuation correction of the emission images.     

Dosimetry of transmission measurements in nuclear medicine: a study using anthropomorphic phantoms and thermoluminescent dosimeters

Quantification in positron emission tomography (PET) and single photon emission tomographic (SPET) relies on attenuation correction which is generally obtained with an additional transmission measurement. Therefore, the evaluation of the radiation doses received by patients needs to include the contribution of transmission procedures in SPET (SPET-TM) and PET (PET-TM). In this work we have measured these doses for both PET-TM and SPET-TM. PET-TM was performed on an ECAT EXACT HR+ (CTI/Siemens) equipped with three rod sources of germanium-68 (380 MBq total) and extended septa. SPET-TM was performed on a DST (SMV) equipped with two collimated line sources of gadolinium-153 (4 GBq total). Two anthropomorphic phantoms representing a human head and a human torso, were used to estimate the doses absorbed in typical cardiac and brain transmission studies. Measurements were made with thermoluminescent dosimeters (TLDs, consisting of lithium fluoride) having characteristics suitable for dosimetry investigations in nuclear medicine. Sets of TLDs were placed inside small plastic bags and then attached to different organs of the phantoms (at least two TLDs were assigned to a given organ). Before and after irradiation the TLDs were placed in a 2.5-cm-thick lead container to prevent exposure from occasional sources. Ambient radiation was monitored and taken into account in calculations. Transmission scans were performed for more than 12 h in each case to decrease statistical noise fluctuations. The doses absorbed by each organ were calculated by averaging the values obtained for each corresponding TLD. These values were used to evaluate the effective dose (ED) following guidelines described in ICRP report number 60. The estimated ED values for cardiac acquisitions were 7.7 x 10(-4) +/- 0.4 x 10(-4) mSv/MBq.h and 1.9 x 10(-6) +/- 0.4 x 10(-6) mSv/MBq.h for PET-TM and SPET-TM, respectively. For brain scans, the values of ED were calculated as 2.7 x 10(-4) +/- 0.2 x 10(-4) mSv/MBq.h for PET-TM and 5.2 x 10(-7) +/- 2.3 x 10(-7) mSv/MBq.h for SPET-TM. In our institution, PET-TM is usually performed for 15 min prior to emission. SPET-TM is performed simultaneously with emission and usually lasts 30 and 15 min for brain and cardiac acquisitions respectively. Under these conditions ED values, estimated for typical source activities at delivery time (22,000 MBq in SPET and 555 MBq for PET), were 1.1 x 10(-1) +/- 0.1 x 10(-1) mSv and 1.1 x 10(-2) +/- 0.2 x 10(-2) mSv for cardiac PET-TM and SPET-TM respectively. For brain acquisitions, the ED values obtained under the same conditions were 3.7 x 10(-2) +/- 0.3 x 10(-2) mSv and 5.8 x 10(-3) +/- 2.6 x 10(-3) mSv for PET-TM and SPET-TM respectively. These measurements show that the dose received by a patient during a transmission scan adds little to the typical dose received in a routine nuclear medicine procedure. Radiation dose, therefore, does not represent a limit to the generalised use of transmission measurements in clinical SPET or PET.     

Magnetic resonance imaging and positron emission tomography of band heterotopia

A case of band heterotopia was reported with findings of positron emission tomography (PET). The patient was an 8-year-old girl who had mild mental retardation and intractable partial epilepsy. Her MRI showed another diffuse layer of gray matter underlying the normal-looking cortex and separated from it by an apparently normal layer of white matter. PET scan with [18F]fluorodeoxyglucose revealed that band heterotopia had the same degree of glucose metabolism as that of the overlying cortex.     

Construction of a food-grade multiple-copy integration system for Lactococcus lactis

We present a clinical evaluation of the quantitative bias which is introduced during simultaneous emission/transmission (SET) acquisition for the application of whole-body positron emission tomography (PET) with fluorine-18 2-fluoro-2-deoxy-d-glucose. The quantitative accuracy of the SET technique was assessed by means of a clinical study involving 28 patients and a realistic phantom experiment. In the clinical study, SET overestimated the activity concentration in the tumours by a factor of approximately 1.10, but in the phantom study, where the tumours were smaller, the bias was found to increase to a value of 1.39. The bias in the soft tissue regions of the patient studies varied between 1.03 and 1.36, and close agreement was observed with the corresponding phantom results. The extent of the bias increased as the local activity concentration decreased and we attribute the effect to scattered photons from the transmission source which are detected in the emission window during SET.     

Noninvasive quantitation of cerebral blood flow using oxygen-15-water and a dual-PET system

Measurement of the arterial input function is essential for quantitative assessment of physiological function in vivo using PET. However, frequent arterial blood sampling is invasive and labor intensive. Recently, a PET system has been developed that consists of two independent PET tomographs for simultaneously scanning the brain and heart, which should avoid the need for arterial blood sampling. The aim of this study was to validate noninvasive quantitation with this system for 15O-labeled compounds. METHODS: Twelve healthy volunteers underwent a series of PET studies after C15O inhalation and intravenous H2(15)O administration using a Headtome-V-Dual tomograph (Shimadzu Corp., Kyoto, Japan). The C15O study provided gated blood-pool images of the heart simultaneously with quantitative static blood-volume images of both the brain and heart. Weighted-integrated H2(15)O sinograms were acquired for estimating rate constant (K1) and distribution-volume (Vd) images in the brain, in addition to single-frame sinograms for estimating autoradiographic cerebral blood flow images. Noninvasive arterial input functions were determined from the heart scanner (left ventricular chamber) according to a previously developed model and compared directly to invasive input functions measured with an on-line beta probe in six subjects. RESULTS: The noninvasive input functions derived from this PET system were in good agreement with those obtained by continuous arterial blood sampling in all six subjects. There was good agreement between quantitative values obtained noninvasively and those using the invasive input function: average autoradiographic regional cerebral blood flow was 0.412 +/- 0.058 and 0.426 +/- 0.062 ml/min/g, K1 of H2(15)O was 0.416 +/- 0.073 and 0.420 +/- 0.067 ml/min/ml and Vd of H2(15)O was 0.800 +/- 0.080 and 0.830 +/- 0.070 ml/ml for the noninvasive and invasive input functions, respectively. In addition to the brain functional parameters, the system also simultaneously provided cardiac function such as regional myocardial blood flow (0.84 +/- 0.19 ml/min/g), left ventricular volume (132 +/- 22 mm at end diastole and 45 +/- 14 ml at end systole) and ejection fraction (66% +/- 5%). CONCLUSION: This PET system allows noninvasive quantitation in both the brain and heart simultaneously without arterial cannulation, and may prove useful in clinical research.     

Attenuation corrected myocardial PET after application of 18FDG: effect on the determination of regional myocardial uptake values

AIM: Post injection transmission measurement (PIT) can be performed using rotating 68Ge/68Ga linesources. This study estimates attenuation coefficients, count densities and relative regional uptake values of PIT corrected cardiac PET (E-PIT) compared to routinely pre-injection transmission measurement (RT). METHODS: A thorax-phantom with homogeneously filled myocardium or with simulated defects and six patients with advanced coronary artery disease were studied using ECAT Exact tomograph (Siemens CTI) equipped with three rotating linesources. Transmission was performed twice (PIT, RT), attenuation coefficients and emission data were analysed, the latter without attenuation correction (E-UK), corrected with PIT (E-PIT) and with RT (E-RT) (count density, standard and relative uptake values). RESULTS: Both in phantom and patient studies attenuation coefficients differed significantly between PIT and RT. Comparing E-PIT and E-RT, regional uptake values were different only in phantom simulation with myocardial radioactivity concentrations higher than 10 kBq x ml-1. The image contrast between defects and remaining myocardium in the phantom studies or the standard and relative uptake values in patient studies did not vary significantly. CONCLUSION: Under clinical conditions a post injection transmission measurement does not influence the accuracy of regional myocardial uptake values relevantly.