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13N-ammonia and 18F-flurpiridaz require longer delays between rest and stress studies to allow for decay, lowering clinical throughput. In this study, we investigated the impact of residual subtraction on MBF and MFR estimates, as well as its effects on diagnostic accuracy. We retrospectively analyzed 63 patients who underwent a dynamic ammonia rest/stress study and 231 patients from the flurpiridaz 301 trial. Residual subtraction was performed by subtracting the mean pre-injection activity in each sampled region from that region’s time activity curve. Corrected and uncorrected MBF and MFR were analyzed. Diagnostic accuracy was compared to quantitative coronary angiograms (QCA) for the flurpiridaz population. With delays between injections above 3 half-lives, and a doubled stress dose, residual activity did not meaningfully increase ammonia MBF (

Purpose A 2-m axial field-of-view, total-body PET/CT scanner (uEXPLORER) has been recently developed to provide total-body coverage and ultra-high sensitivity, which together, enables opportunities for in vivo time-activity curve (TAC) measurement of all investigated organs simultaneously with high temporal resolution. This study aims at quantifying the cumulated activity and patient dose of 2-[F-18]fluoro-2-deoxy-D-glucose (F-18 FDG ) imaging by using delayed time-activity curves (TACs), measured out to 8-h post-injection, for different organs so that the comparison between quantifying approaches using short-time method (up to 75 min post-injection) or long-time method (up to 8 h post-injection) could be performed. Methods Organ TACs of 10 healthy volunteers were collected using total-body PET/CT in 4 periods after the intravenous injection of F-18 FDG. The 8-h post-injection TACs of 6 source organs were fitted using a spline method (based on Origin (version 8.1)). To compare with cumulated activity estimated from spline-fitted curves, the cumulated activity estimated from multi-exponential curve was also calculated. Exponential curve was fitted with shorter series of data consistent with clinical procedure and previous dosimetry works. An 8-h dynamic bladder wall dose model considering 2 voiding were employed to illustrate the differences in bladder wall dose caused by the different measurement durations. Organ absorbed doses were further estimated using Medical Internal Radiation Dose (MIRD) method and voxel phantoms. Results A short-time measurement could lead to significant bias in estimated cumulated activity for liver compared with long-time-measured spline fitted method, and the differences of cumulated activity were 18.38% on average. For the myocardium, the estimated cumulated activity difference was not statistically significant due to large variation in metabolism among individuals. The average residence time differences of brain, heart, kidney, liver, and lungs were 8.38%, 15.13%, 25.02%, 23.94%, and 16.50% between short-time and long-time methods. Regarding effective dose, the maximum differences of residence time between long-time-measured spline fitted curve and short-time-measured multi-exponential fitted curve was 9.93%. When using spline method, the bladder revealed the most difference in the effective dose among all the investigated organs with a bias up to 21.18%. The bladder wall dose calculated using a long-time dynamic model was 13.79% larger than the two-voiding dynamic model, and at least 50.17% lower than previous studies based on fixed bladder content volume. Conclusions Long-time measurement of multi-organ TACs with high temporal resolution enabled by a total-body PET/CT demonstrated that the clinical procedure with 20 min PET scan at 1 h after injection could be used for retrospective dosimetry analysis in most organs. As the bladder content contributed the most to the effective dose, a long-time dynamic model was recommended for the bladder wall dose estimation.

The aim of this study was to assess whether dynamic PET with 11C-methionine (MET) (MET-PET) is useful in the diagnosis of brain tumors. One hundred sixty patients with brain tumors (139 gliomas, 9 meningiomas, 4 hemangioblastomas and 8 primary central nervous system lymphomas [PCNSL]) underwent dynamic MET-PET with a 3-dimensional acquisition mode, and the maximum tumor MET-standardized uptake value (MET-SUV) was measured consecutively to construct a time-activity curve (TAC). Furthermore, receiver operating characteristic (ROC) curves were generated from the time-to-peak (TTP) and the slope of the curve in the late phase (SLOPE). The TAC patterns of MET-SUVs (MET-TACs) could be divided into four characteristic types when MET dynamics were analyzed by dividing the MET-TAC into three phases. MET-SUVs were significantly higher in early and late phases in glioblastoma compared to anaplastic astrocytoma, diffuse astrocytoma and the normal frontal cortex (P

PURPOSE This study aimed to evaluate the novel index of hepatic receptor (IHR) on the regression analysis derived from time activity curve of the liver for hepatic functional reserve. METHODS Sixty patients had undergone (99m)Tc-galactosyl serum albumin ((99m)Tc-GSA) scintigraphy in the retrospective clinical study. Time activity curves for liver were obtained by region of interest (ROI) on the whole liver. A novel hepatic functional predictor was calculated with multiple regression analysis of time activity curves. In the multiple regression function, the objective variables were the indocyanine green (ICG) retention rate at 15 min, and the explanatory variables were the liver counts in 3-min intervals until end from beginning. Then, this result was defined by IHR, and we analyzed the correlation between IHR and ICG, uptake ratio of the heart at 15 minutes to that at 3 minutes (HH15), uptake ratio of the liver to the liver plus heart at 15 minutes (LHL15), and index of convexity (IOC). RESULTS Regression function of IHR was derived as follows: IHR=0.025×L(6)-0.052×L(12)+0.027×L(27). The multiple regression analysis indicated that liver counts at 6 min, 12 min, and 27 min were significantly related to objective variables. The correlation coefficient between IHR and ICG was 0.774, and the correlation coefficient between ICG and conventional indices (HH15, LHL15, and IOC) were 0.837, 0.773, and 0.793, respectively. IHR had good correlation with HH15, LHL15, and IOC. CONCLUSIONS The finding results suggested that IHR would provide clinical benefit for hepatic functional assessment in the (99m)Tc-GSA scintigraphy.

Dynamic Positron Emission Tomography (PET) allows quantification of underlying physiological processes in a tissue or organ of interest by modeling the radioactivity concentration measured in time (time-activity curve, i.e. TAC). Although the [11C]-(R)-PK11195 PET radiotracer binds to activated microglia and therefore images neuroinflammation, its quantification is still challenging. The aim of this study was to investigate a novel method for analyzing [11C]-(R)-PK11195 TAC behavior from dynamic PET. Seven healthy subjects underwent dynamic 60 min [11C]-(R)-PK11195 PET scans, and TACs were generated for 30 brain cortical regions using the AAL-Merged atlas. The proposed method supposes healthy subjects have similar TACs, which allows the construction of a “healthy template”. Then, TACs of patients can be compared to the healthy template to determine the likelihood that their behavior is abnormal. To evaluate the differences between a healthy region and an inflamed region, a cut-off value for abnormality was created. The method was then tested on a multiple sclerosis (MS) patient. The proposed method was able to identify a number of brain cortical regions with distinct behavior in one MS patient as compared to the healthy template. Further studies are required to evaluate the applicability of the proposed method with additional MS patients, and with data acquired in different scanners and reconstructed with other algorithms.

Major management decisions in patients with solid tumors and lymphomas are often based on 18F-fluorodeoxyglucose (18F-FDG) PET/CT. The misadministration of 18F-FDG outside the systemic circulation can have an adverse impact on this test's sensitivity (1) and is not uncommon (2–7). This report describes how an 18F-FDG misadministration led to a repeat PET/CT study, resulting in the visualization of distant metastases that changed the original treatment plan. The findings suggest that routine injection monitoring is indicated whenever sensitivity is critical, and support claims that infiltrations can confound interpretation of semi-quantitative PET outcome measures in patients who are followed longitudinally (2).

F-fluoroethyltyrosine (FET) is a well-established PET tracer for the imaging of cerebral gliomas. Recent studies reported interest in meningiomas. A study published by Cornelius et al concludes that FET PET may provide additional information for noninvasive grading of meningiomas. Indeed, the combination of tumor background ratio with a cutoff value of 2.3 associated with time activity curve pattern slightly improved the differentiation of high-grade from low-grade meningiomas (accuracy, 92%; P = 0.001). We present the case of a 75-year-old man that underlined the need to confirm the performance of these tools (curve pattern, tumor background ratios) to characterize meningiomas.

177Lu-DOTATATE therapy has been shown to produce encouraging results in treatment of neuroendocrine tumours (NETs). Unfortunately, since dosimetry for radionuclide therapy is considered to be challenging, typically similar amount of radiopharmaceutical is administered to every patient. There is growing evidence that the efficacy of this therapy can be significantly improved by employing personalized protocols, based on the organ-at-risk dosimetry. The aim of this study is to propose a practical and accurate dosimetry protocol based on the simplified acquisition schedules. Data from fifty-three therapy cycles in thirty-nine NET patients were analyzed. Three SPECT/CT scans, acquired at 4 h (D0), 23 h (D1) and 70 h (D3) after injection, were performed. The kidney volume was determined using CT and the activity was determined from quantitative SPECT using an iterative thresholding method. For each dataset, four methods were used to model the time-activity-curves (TAC): M1-two trapezoid segments (0 to D0 and D0 to D1), followed by monoexponential fit to D1 + D3 data; M2-monoexponential fit to D0 + D1 + D3 data; M3 and M4-monoexponential fit to D0 + D3 and D1 + D3 data, respectively. Additionally, kidney doses obtained from single time point method using a monoexponential curve with the population mean effective half-life, normalized to activities at D0 or D1 or D3 points, were calculated. The accuracy of simplified dosimetry methods was assessed as the percentage difference relative to doses calculated from M1. The major contribution to the absorbed dose estimate comes from the area under the late time portion of the TAC (D1 to infinity). Therefore, information from the late scan (D3) is crucial for the determination of kidney absorbed doses. Single time point method using monoexponential TAC, with the population mean effective half-life normalized to the late data point (48-72 h for kidneys) produces

Background The convolution approach to thyroid time-activity curve (TAC) data fitting with a gamma distribution convolution (GDC) TAC model following bolus intravenous injection is presented and applied to 99mTc-MIBI data. The GDC model is a convolution of two gamma distribution functions that simultaneously models the distribution and washout kinetics of the radiotracer., The GDC model was fitted to thyroid region of interest (ROI) TAC data from 1 min per frame 99mTc-MIBI image series for 90 min; GDC models were generated for three patients having left and right thyroid lobe and total thyroid ROIs, and were contrasted with washout-only models, i.e., less complete models. GDC model accuracy was tested using 10 Monte Carlo simulations for each clinical ROI. Results The nine clinical GDC models, obtained from least counting error of counting, exhibited corrected (for 6 parameters) fit errors ranging from 0.998% to 1.82%. The range of all thyroid mean residence times (MRTs) was 212 to 699 min, which from noise injected simulations of each case had an average coefficient of variation of 0.7% and a not statistically significant accuracy error of 0.5% (p = 0.5, 2-sample paired t test). The slowest MRT value (699 min) was from a single thyroid lobe with a tissue diagnosed parathyroid adenoma also seen on scanning as retained marker. The two total thyroid ROIs without substantial pathology had MRT values of 278 and 350 min overlapping a published 99mTc-MIBI thyroid MRT value. One combined value and four unrelated washout-only models were tested and exhibited R-squared values for MRT with the GDC, i.e., a more complete concentration model, ranging from 0.0183 to 0.9395. Conclusions The GDC models had a small enough TAC noise-image misregistration (0.8%) that they have a plausible use as simulations of thyroid activity for querying performance of other models such as washout models, for altered ROI size, noise, administered dose, and image framing rates. Indeed, of the four washout-only models tested, no single model approached the apparent accuracy of the GDC model using only 90 min of data. Ninety minutes is a long gamma-camera acquisition time for a patient, but a short a time for most kinetic models. Consequently, the results should be regarded as preliminary.

Purpose: Numerous new drug candidates fail because of inadequate pharmacokinetics. Positron emission tomography(PET) enables the noninvasive characterization of the drug in humans and animals. The aim of the present work was the comparison of methods for the extraction of organ time activity curves from rodent PETimages without requiring resort to anatomical information. Methods: The rodent organs were segmented using the local means analysis method and the accuracy of the time activity curve (TAC) estimated using four methods was compared: The mean TAC (Mean), the TAC computed in a selection of organ voxels (ROIopt), and the TAC corrected for partial volume effect using the geometric transfer matrix (GTM) method. The accuracy of the TAC estimated using the three methods was compared on phantom simulations and on experimental data sets on mice injected with fluorothymidine. Results: The segmentation quality measured on phantom simulation was 80% of overlap between segmented and gold standard organs. On the phantom simulations, the error on the TAC estimation on phantom simulations was lower for ROIopt (8%) than using the GTM (18%) and the Mean (27%) methods. Similar results were achieved on the experimental data sets: ROIopt (5.8%), GTM (9.7%), and Mean (12%). Conclusions: The new ROI optimization method was fast and precise for all homogeneous organs, while mean organ TAC computation led as expected to important errors. GTM improved the quantification accuracy but showed instabilities due to segmentation errors and to small organ sizes. Partial volume effect correction or limitation is thus possible for the extraction of precise organ TACs without requiring either manual delineation or an anatomical modality.

Purpose: To develop an unsupervised tumor delineation method based on time-activity curve (TAC) shape differences between tumor tissue and healthy tissue and to compare the resulting contour with the two tumor contouring methods mostly used nowadays. Methods and Materials: Dynamic positron emission tomography-computed tomography (PET-CT) acquisition was performed for 60 min starting directly after fluorodeoxyglucose (FDG) injection. After acquisition and reconstruction, the data were filtered to attenuate noise. Correction for tissue motion during acquisition was applied. For tumor delineation, the TAC slope values were k-means clustered into two clusters. The resulting tumor contour (Contour I) was compared with a contour manually drawn by the radiation oncologist (Contour II) and a contour generated using a threshold of the maximum standardized uptake value (SUV; Contour III). Results: The tumor volumes of Contours II and III were significantly larger than the tumor volumes of Contour I, with both Contours II and III containing many voxels showing flat TACs at low activities. However, in some cases, Contour If did not cover all voxels showing upward TACs. Conclusion: Both automated SUV contouring and manual tumor delineation possibly incorrectly assign healthy tissue, showing flat TACs, as being malignant. On the other hand, in some cases the manually drawn tumor contours do not cover all voxels showing steep upward TACs, suspected to be malignant. Further research should be conducted to validate the possible superiority of tumor delineation based on dynamic PET analysis. (c) 2009 Elsevier Inc.

Background The objective of this study is to determine the radiation dosimetry of a novel radiotracer for vesicular acetylcholine transporter (−)-(1-((2R,3R)-8-(2-[18F]fluoro-ethoxy)-3-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)piperidin-4-yl)(4-fluorophenyl)-methanone ([18F]VAT) based on PET imaging in nonhuman primates. [18F]VAT has potential for investigation of neurological disorders including Alzheimer’s disease, Parkinson’s disease, and dystonia. Methods Three macaque fascicularis (two males, one female) received 185.4–198.3 MBq [18F]VAT prior to whole-body imaging in a MicroPET-F220 scanner. Time activity curves (TACs) were created from regions of interest (ROIs) that encompassed the entire small organs or samples with the highest activity within large organs. Organ residence times were calculated based on the TACs. We then used OLINDA/EXM 1.1 to calculate human radiation dose estimates based on scaled organ residence times. Results Measurements from directly sampled arterial blood yielded a residence time of 0.30 h in agreement with the residence time of 0.39 h calculated from a PET-generated time activity curve measured in the left ventricle. Organ dosimetry revealed the liver as the critical organ (51.1 and 65.4 μGy/MBq) and an effective dose of 16 and 19 μSv/MBq for male and female, respectively. Conclusions The macaque biodistribution data showed high retention of [18F]VAT in the liver consistent with hepatobiliary clearance. These dosimetry data support that relatively safe doses of [18F]VAT can be administered to obtain imaging in humans.

In this study, we developed a simple and robust semi-automatic method to measure the right ventricle to left ventricle (RV-to-LV) transit time (TT) in mice using 2-[/sup 18/F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). The accuracy of the method was first evaluated using a 4-D digital dynamic mouse phantom. The RV-to-LV TTs of twenty-nine mouse studies were measured using the new method and compared to those obtained from the conventional ROI-drawing method. The results showed that the new method correctly separated different structures (e.g., RV, lung, and LV) in the PET images and generated corresponding time activity curve (TAC) of each structure. The RV-to-LV TTs obtained from the new method and ROI method were not statistically different (p=0.20; r=0.76). We expect that this fast and robust method is applicable to the pathophysiology of cardiovascular diseases using small animal models such as rats and mice.

OBJECTIVE In-vivo quantitative cerebral blood flow (CBF) measurement using positron emission tomography (PET) has typically employed invasive arterial blood sampling procedure to determine the arterial input function (AIF). The present study was performed to provide a non-invasive quantitative CBF measurement technique for rats using a dedicated animal PET. METHODS CBF was measured in 10 male rats (Fischer 344, 247-290 g) under alpha-chloralose anesthesia (30 mg x kg . h, intravenous infusion) by dynamic PET imaging employing the intravenous bolus injection of H2(15)O. Unlike other conventional PET methods, no arterial blood sampling was employed. Instead, a cardiac time-activity curve (TAC) obtained from the dynamic PET imaging was used to determine the AIF. For the validation of this technique, CBF was also measured by calculating the washout rate of the tracer (H2(15)O) following an intracarotid bolus injection. CBF measurements by two independent methods were done while modulating and maintaining the body temperature at two different levels (32+/-1 and 37+/-1 degrees C by the rectal temperature). Two methods were compared by the linear regression analysis. RESULTS CBF (ml x 100 g x min) values (mean+/-SD) were 45.2+/-6.05 (intravenous) and 47.4+/-8.64 (intracarotid) at the hypothermic condition (32 degrees C), and 55.1+/-4.88 (intravenous) and 54.4+/-4.60 (intracarotid) at the normothermic condition (37 degrees C). There was a good agreement between the two methods (r=0.70). CONCLUSIONS Our cardiac TAC analysis technique for small animals can be used for the non-invasive quantification of CBF using the PET-based in-vivo imaging technique.

International audience; This paper describes a new method for assessing clinical parameters from a noisy regional time-activity curve (TAC) in tomographic gated blood-pool ventriculography. This method is based on a priori knowledge on the shape of a TAC, and shape approximation. The rejection method was used to generate different random Poisson deviates, covering standard count levels, of six representative TACs in order to test and compare the proposed method with harmonic and multiharmonic reconstruction methods. These methods were compared by evaluating four clinical parameters: time of end systole, amplitude, peak ejection and filling rates. Overall, the accuracy of assessment of these parameters was found to be better with the method described in this paper than with standard multiharmonic fits.

The validation study is described of a new modelling method that has been developed, using tracer kinetic modelling with positron emission tomography (PET) to achieve non-invasive measurement of myocardial metabolic rate of glucose (MMRGlc). Eight data sets obtained from dynamic cardiac PET 2-[18F]fluoro-2-deoxy-D-glucose (FDG) studies on human subjects are employed, and the estimation of MMRGlc using both the new and traditional methods is compared. The results from all eight human FDG studies are consistent with those from previous computer simulations. With the new method, the estimated mean of K (a parameter directly proportional to MMRGlc) increases by about 8%, and that of k 4 (the rate constant of FDG dephosphorylation) decreases by about 48%. The approach should be more suitable for use in dynamic cardiac PET studies when non-invasive means are used to obtain the plasma time-activity curve from left-ventricle PET images.

Background. In physiologic situations age, heart rate (HR) and left ventricular ejection fraction (EF) may influence left ventricular filling rate. In this study, we determined normal values for radionuclide angiography (RNA) derived diastolic filling parameters, the correlations with age, HR and EF and their reproducibility. Methods. The study was performed in 20 patients, 40–76 years old (mean 57), with normal findings at coronary angiography and left ventriculography. The first RNA was performed at rest (RNA1). Then, five minutes bicycle ergometry was performed and the patients were allowed five minutes rest before RNA was repeated (RNA2). From the left ventricular time activity curve we determined peak filling rate (PFR), time to peak filling rate (TPFR) and atrial contribution (AC) to ventricular filling. Results. Values for PFR1 were 2.2 ± 0.6 EDV/sec (PFR2 2.4 ± 0.7 EDV/sec, r = 0.82), for TPFR1 198 ± 22 msec (TPFR2 203 ± 24 msec, r = 0.45) and for AC1 31 ± 11% (AC2 31 ± 10%, r = 0.72). The correlations of PFR and TPFR with age were statistically significant (respectively r = - 0.68 and r = 0.48, P < 0.05). PFR was also influenced by HR and EF (resp. r = 0.51 and r = 0.50, P < 0.05). TPFR however was not influenced by HR and EF, whereas AC was positively correlated with HR (r = 0.79, P < 0.01). Conclusions. Radionuclide angiography is a reliable and reproducible method to assess parameters of diastolic left ventricular filling in individual patients. It may therefore be used to serially follow diastolic function. When used for interindividual comparison the dependency of RNA derived left ventricular filling parameters on age, HR and EF should however be considered.

Quantitative measurements of cerebral blood flow (CBF) are performed in a volume imaging PET scanner by means of moderate activity infusions. In equilibrium infusions, activations are measured by scanning over 10 minutes with 16 minute activations. Typical measured whole brain CBF values are 37/spl plusmn/8 ml/min/100 g, close to the value of 42 ml/min/100 g reported by other groups using this method. For ramped infusions, scanning over 4 minutes with 5 minute activations results in whole brain CBFs of 49/spl plusmn/9 ml/min/100 g, close to the Kety and Schmidt value of 50 ml/min 100 g. Both equilibrium and ramped infusion methods have been used to study face and word memory in human subjects. Both methods were able to detect significant activations in regions implicated in human memory. We conclude that precise quantitation of regional CBF is achieved using both methods, and that ramped infusions also provide accurate measures of CBF. In addition a simplified protocol for ramped infusion studies has been developed. In this method the whole brain tissue time activity curve generated from dynamic scanning is replaced by an appropriately scaled camera coincidence countrate curve. The resulting whole brain CBF values are only 9% different from the dynamic scan and fit results. Regional CBFs (rCBF) may then be generated from the summed image (4.25 minutes) using a count density vs flow lookup table. >

Miniature detector probes have previously been used in large animal models to investigate myocardial 201Tl clearance kinetics. The results of these studies helped develop clinical imaging protocols that greatly improved the accuracy of thallium scintigraphy. However, miniature detector probes are too large to be used in small animals. Thus, if a method could be developed to measure regional time activity curves in small animals, it would provide a cost-effective alternative to both experiments in large animals and/or multiple experiments at varying time points that can produce results only by postmortem analysis of several animals. Accordingly, we developed a method to measure a regional time activity curve of a tracer in rabbits by using a series of thin thermoluminescent dosimeters [CaF2 (dopant) TLDs, 1 mm thick] placed on the surface of the myocardium. Background contributions associated with high blood pool activity are modeled and then subtracted from the initial TLD response. To validate and illustrate this method, thallium kinetics were determined for nonischemic rabbit myocardium (n = 6). Myocardial thallium concentration decreased monoexponentially with a mean half-time equal to 396 +/- 141 min. Arterial blood activity decreased triexponentially with a final half-time of 243 +/- 73 min. No significant difference was found when the myocardial half-time was compared to the final arterial half-time. These findings are consistent with previous work using a cadmium telluride probe in a canine model. Therefore, TLD analysis can provide a cost-effective, reliable, and reproducible method to measure regional myocardial clearance kinetics.

In a dynamic Positron Emission Tomography (PET) scan, the blood pool (BP) time activity curve forms the input function in a compartmental model technique for evaluation of rate constants to measure myocardial glucose uptake and utilization in vivo. Several methods have been described in the literature for arterial blood sampling, which is the accepted gold standard for measurement of the blood input function [1-3]. A major problem with image-derived blood input function (IDIF) method is that it is susceptible to Spillover (SP) and Partial Volume (PV) effects more so at the early time points due to rapid metabolism and also at the late time points due to cellular trapping of 2-[18F] fluoro-2deoxy-D-glucose (FDG) .

Arterial and venous systems are the main points for the evaluation of vasculogenic impotence. To evaluate both of these systems in the same study we propose a dual radioisotopic study in which technetium-99m (Tc-99m) and xenon-133 (Xe-133) were used. The changes in Tc-99m and Xe-133 radioactivities administered intravenously and intracavernously, respectively, were monitored before and after intracavernous papaverine injection. These changes were determined as time activity curves, which were generated from the region of interest over the penis. A Tc-99m penogram index derived from the Tc-99m time activity curve was significantly different in the control and arteriogenic impotence groups (131.67 +/- 74.6 versus 62.94 +/- 51.6, p < 0.01). A meaningful correlation between Tc-99m penogram index results and duplex ultrasonographic findings were observed (r = 0.905). Xe-133 penogram index, derived from the Xe-133 washout curve was significantly different in the control and venogenic impotence groups (-25.65 +/- 24.9 versus -56.09 +/- 13.4, p < 0.01). Also, a meaningful correlation was obtained between pharmacocavernosometry and Xe-133 penogram index results of venogenic impotent patients (r = 0.86). These findings suggest that the dual radioisotopic study will be a useful technique in the evaluation of the entire vascular system of the penis, since it is a noninvasive method.

Salivary gland scintigraphy with 99mTcO4- is a simple method to evaluate salivary gland function and has been available as a technique using a time/activity curve for a number of years. But, there were few reports on the relationship between the various patterns of the time/activity curvcs and the salivary flow rate from the gland. This presents correlation between the time/activity curve pattern and the salivary flow rate from the parotid gland.65 patients complaining of xerostomia were examined.62 were female and 3 male (average age 45.6 years, range 17-69years).Their diagnosis were 26 Sjogren Syndrome, 28 suspicion of Sjogren Syndrome and 11 parotiditis.The salivary flow rate from parotid gland was measured by stimulation with 10% citric acid using modified Carlson crittenden cup every 10 seconds for 5 min. 185 MBq 99mTcO4-was injected intravenously and sequential scintigraphy was perfbrmed. Time/activity curves were recorded on film. Six kinds of basic patterns werc followed; Normal pattern, Median pattern, Flat pattern and Sloped pattern (Mita et al 1981), Reaccumulation flat pattern and Poor secretion (Stimulant secretory ratio: less than 70%) pattern by us. The amount of saliva was as follows; Normal pattern (n=31): 5.4+0.4ml, Reaccumulation flat pattern (n=3): 4.2+0.6ml, Poor secretion pattern (n=18): 4.1+0.5ml, Median pattern (n=20): 3.5+0.5ml, Flat pattern (n=11): 2.6+0.5ml and Sloped pattern (n=1): 1.5ml. Normal pattern versus Poor secretion pattern, Median pattern and Flat pattern in the salivary flow rate were statistically significant as determined by Students, t-test.We assessed the correlation between the pattern of time/activity curve in the salivary gland scintigraphy and the amount of saliva.

The term input function usually refers to the tracer plasma time activity curve (pTAC), which is necessary for quantitative positron emission tomography (PET) studies. The purpose of this study was to acquire the pTAC from the independent component analysis (ICA) estimated whole blood time activity curve (wTAC) using our proposed method: FDG blood-cell-two-compartment model (BCM). We also compared published models, which are linear haematocrit (HCT) correction, nonlinear HCT correction, and two-exponential correction. According to the results, the normalized root mean square error (NRMSE) and error of area under curve (EAUC) of BCM estimated pTAC were the smallest. Compartmental and graphic analyses were used to estimate metabolic rate of FDG (MR FDG ). The percentage error of MR FDG (PE MRFDG ) estimated from BCM corrected pTAC was also the smallest. The BCM is a better choice to transfer wTAC to pTAC for quantification.

PET is an imaging modality widely used in areas such as oncology, neurology, cardiology and neuropsychology/cognitive neuro-science. Dynamic PET, in contrast to static PET, can identify temporal variations in the radiotracer concentration. Mathematical modeling of the tissue of interest in dynamic PET can be simplified using compartment models as a linear system where the time activity curve of a specific tissue is the convolution of the tracer concentration in the plasma and the impulse response of the tissue containing kinetic parameters. Since the arterial sampling of blood to acquire the value of the tracer concentration is invasive, blind identification to estimate both the blood input function and the kinetic parameters has recently drawn attention. Several methods have been developed for this purpose, but the effect of the estimated blood on the estimation of the kinetic parameters is not studied. In this paper, we present a mathematical model to compute the error in the kinetic parameter estimates caused by the error in estimation of the blood input function. Computer simulations show that analytical expressions we derive are sufficiently close to results obtained from optimization. Our findings are conceptually important to observe the effect of the blood function on kinetic parameter estimation, but also practically useful to evaluate various blind methods.

The authors analyzed the left atrial (LA) time activity curve (TAC) in 18 normal subjects and 30 patients with mitral regurgitation (MR) to assess the usefulness of radionuclide ventriculography (RNV) in detecting MR. The LA TAC was generated from gated blood pool images using phase and amplitude images. The configuration of normal LA TAC was M shaped. The first peak and last peak of LA TAC were represented as points B and D, respectively. In addition, the trough following B was named point C. The presence and severity of MR was analyzed by use of three methods: (1) analysis of LA TAC, (2) analysis of left ventricular TAC, and (3) measurement of the stroke count ratio of left ventricle to right ventricle. In the diagnosis of MR using RNV, the rapid emptying fraction [REF:(B-C)/ (B-A)] of LA TAC was the most sensitive index compared with the other two methods. The sensitivity and specificity of MR with Sellers' II° or more were 0.84 and 0.90 in LA TAC but were 0.42 and 0.90 in the count method.

The term input function usually refers to the tracer plasma time activity curve (pTAC), which is necessary for quantitative positron emission tomography (PET) studies. The purpose of this study was to acquire the pTAC by independent component analysis (ICA) estimation from the whole blood time activity curve (wTAC) using a novel method, namely the FDG blood-cell-two-compartment model (BCM). This approach was compared to a number of published models, including linear haematocrit (HCT) correction, non-linear HCT correction and two-exponential correction. The results of this study show that the normalized root mean square error (NRMSE) and the error of the area under curve (EAUC) for the BCM estimate of the pTAC were the smallest. Compartmental and graphic analyses were used to estimate the metabolic rate of the FDG (MR"F"D"G). The percentage error for the MR"F"D"G (PE"M"R"F"D"G) was estimated from the BCM corrected pTAC and this was also the smallest. It is concluded that the BCM is a better choice when transferring wTAC into pTAC for quantification.

Measurement of distribution volume with the Logan plot requires an arterial time activity curve (TAC). The gold standard for measuring arterial activity concentrations is arterial blood sampling. Arterial cannulation carries with it several risks. This work simulated the effects of venous dispersion on measured distribution volumes using the Logan plot with a venous TAC. A representative arterial TAC was selected from a patient study. Simulated tissue TACs were generated from a three compartment kinetic model using the representative arterial TAC. Venous TACs were simulated by convolving the arterial TAC with modified transit time spectra derived from an in vivo dynamic contrast enhanced-CT forearm study. Gaussian noise was added to the tissue TACs. Logan analysis was compared using the arterial and venous TACs for a wide range of kinetic parameters. Bland–Altman analysis was performed to assess agreement between the two methods. Good agreement was observed between values calculated with the arterial and simulated venous TACs for both noiseless and noisy cases. Agreement was slightly dependent on the arterio–venous extraction efficiency of the PET tracer. Results suggest that venous sampling may be a feasible alternative to arterial sampling for analysis with the Logan plot. This technique must be clinically validated in future patient studies.

A study aimed at the extraction of kinetic information from clinical cardiac SPECT is presented. A dual head SPECT system with high resolution parallel-hole collimators was used for imaging the distribution and kinetics of 201Tl at rest and 99mTc-sestamibi at stress in the myocardium of patients. Dynamic acquisition was performed for each pharmaceutical by acquiring 48 tomographic projection sets over a 30 min period. Both the dynamic datasets and the summed dataset were reconstructed using a standard voxelized reconstruction approach and a new point cloud grid multi-resolution representation. ROI analysis was used to extract dynamic information from the scan data acquired 30 seconds or more after the start of acquisition. Since the dynamics of the initial injected bolus are too fast in order to obtain a consistent tomographic data set during the first 36 seconds of the scan, an estimate of the time activity curve for the blood input was obtained by applying factor analysis directly to the projections. Time basis functions and expansion coefficients for each image element in the point cloud representation were estimated from projections using conjugate gradient optimization.

We characterize spillover (SP) and recovery coefficients (RC) in the gated mouse heart to address the feasibility of extracting the plasma time activity curve (pTAC) from the left-ventricle (LV) blood pool during the diastolic phase of the cardiac cycle. The pTAC can be formulated as pTAC(t) = alphaCLV(t) - betaCMYO(t) where alpha and beta are functions of the LV RC, rLV; myocardial RC, rm; myocardium to LV SP, smb; and LV to myocardium SP, sbm. We use anatomical images of the digital mouse phantom undergoing both cardiac and respiratory motion at 0.005sec increments to simulate continuous microPET mouse data. The microPET images were smoothed with FWHM = 1.7mm and summed to produce 8-gate cardiac images. Diastolic images were used to characterize temporal and average SP and RC values in the presence and absence of both cardiac and respiratory gating. To test the sensitivity of RC and SP to mouse heart dimension, we scaled the 3D volume of the heart by -20% to 20% of its original size and repeated the above analysis. Assuming a 1-sec frame duration, average SP and RC values were not significantly different across frames. Of the four coefficients, smb is most sensitive to heart dimension followed by rm, rb, and sbm. For example, at -10% scaling of the heart the bias attributed to alpha and beta is 4% and 12%, respectively. These results suggest that appropriate characterization of SP and RC would enable to extract the pTAC from the LV.

In this study, we developed a simple and robust semiautomatic method to measure the right ventricle to left ventricle (RV-to-LV) transit time (TT) in mice using 2-[18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). The accuracy of the new method was first evaluated using a 4-D digital dynamic mouse phantom. The RV-to-LV TTs of thirty-two mice studies were measured using the new method and compared to those obtained from the conventional ROI-drawing method. The results showed that the new method accurately separated different structures (e.g. RV, lung and LV) in the PET images and generated corresponding time activity curve (TAC) of each structure. The RV-to-LV TTs obtained from the new method and ROI method were not statistically different (p=0.31; r=0.77). We expect that this fast and robust method is applicable to study the pathophysiology of cardiovascular diseases using small animal models such as rats and mice.

In this study, we evaluated the temporal resolution of a new microPET system in mice. We then applied the high resolution capability for determining the cardiovascular transit time which is an important physiological parameter in the study of animal models of cardiovascular disease. Two groups of mice, group 1 (n=12) with high body weight and group 2 (n=10) with low body weight, were studied. Each mouse was injected with a 18F-deoxyglucose (FDG; 40-50 /spl mu/L; 8-48 MBq) bolus and a list mode PET acquisition was started. MicroCT was performed for attenuation correction. We histogrammed the first 9 seconds of the list mode data into frames of 0.2 s-0.5 s duration. After the images were reconstructed and attenuation corrected, the ROIs were assigned to the following structures: vena cava, right and left ventricle blood pool (RV&LV), left lung and aorta. A time activity curve (VAC) of each ROI was generated. To correct for the recirculation, the end of each TAC was approximated by an exponential decay curve. The transit time (TT) was then calculated as the difference of the mean arrival times of the bolus in RV and LV. Short time frames of 0.3 s proved to be the best in terms of reducing noise and at the same being able to follow the rapid physiological processes. The peaks of the TACs showed good separation in various structures if the time spread of the bolus in the vena cava measured as full width of half maximum (FWHM) was shorter than 2 s. Group 1 had significantly (p

A reliable, semi-automated method for estimation of a minimally-invasive image-derived input function is validated for human [ 18 F]-fluoro deoxyglucose (FDG) positron emission tomography (PET) studies. Two time windows can be recognized in the time activity curve measured from a carotid artery region of interest (CA-ROI). During the first short window of very rapid change, the dominant contamination of the measured activity on the CA-ROI is due to partial volume effects. After this the measured activity is also contaminated by spillover of tracer from tissue to blood. Blood samples acquired at later times, free of both partial volume and spillover effects, avoid the contamination and are used to fit a functional form for the input. Appropriateness of this parameter dependent input is validated using data from 18 healthy subjects and contrasted against measured arterial blood samples, and with previously proposed representations [1]–[3]. Parameters defining the input function and micro parameters of each tissue cluster, (their rate constants K1, k2 and k3), [4], are estimated simultaneously using the compartmental model for FDG PET [5].

A compartment model has been used for kinetic analysis of dynamic positron emission tomography (PET) data [e.g., 2-deoxy-2-/sup 18/F-fluoro-D-glucose (FDG)]. The input function of the model [the plasma time-activity curve (pTAC)] was obtained by serial arterial blood sampling. It is of clinical interest to develop a method for PET studies that estimates the pTAC without needing serial arterial blood sampling. For this purpose, we propose a new method to extract the pTAC from the dynamic brain PET images using a modified independent component analysis [extraction of the pTAC using independent component analysis (EPICA). Source codes of EPICA are freely available at http://www5f.biglobe.ne.jp//spl ap/ukimura/Software/top.html]. EPICA performs the appropriate preprocessing and independent component analysis (ICA) using an objective function that takes the various properties of the pTAC into account. After validation of EPICA by computer simulation, EPICA was applied to human brain FDG-PET studies. The results imply that the EPICA-estimated pTAC was similar to the actual measured pTAC, and that the estimated blood volume image was highly correlated with the blood volume image measured using /sup 15/O-CO inhalation. These results demonstrated that EPICA is useful for extracting the pTAC from dynamic PET images without the necessity of serial arterial blood sampling.

PET and SPECT have been widely used to investigate the physiological function of animals in vivo. However, little efforts have been done to estimate absolute physiological parameters, i.e. blood flow of small animals. The present study was aimed at the absolute quantitation of myocardial blood flow of rats by means of the dynamic SPECT fitted with a pinhole collimator with a careful determination of the arterial input function (IF). The center-of-rotation was carefully aligned to the center of the field-of-view of a fixed gamma camera with the accuracy < 0.05 mm. A rat was placed on a rotating device that fixes the rat in a stand position. The arterial blood samples were frequently collected and their radioactivity concentration was measured using a well counter cross-calibrated to the SPECT images. Dynamic SPECT (the step-and-shoot mode) was initiated at 5 min after the injection of 201TlCl into the tail vein. Acquisition period was 10 sec at each rotation angle, and 120 view projection data were obtained. The 360-degree complete data sets were obtained at approximately 20 min interval for 5 time frames. Images were reconstructed by filtered-back projection technique with Feldkamp algorithm. The cross-calibration factor was determined using a cylindrical phantom of 5 cm diameter filled with the 201TlCl solution. Regions-of-interest were placed on the left ventricular wall to generate the tissue time activity curve (TTAC). TTAC and IF were fitted to the previously validated single-tissue compartment model to estimate the regional myocardial blood flow (rMBF) and volume of distribution (Vd) of thallium. The present system provided clear images of myocardial uptake of 201TlCl, and the time-dependent change of the tissue radioactivity concentration in regional basis, which was statistically sufficient for applying the compartment model analysis. The kinetic analysis yielded the rMBF of approximately 0.77 ml/min/g, which appeared to be an acceptable value with a consideration of contribution of partial volume effect and other error sources. Vd of approximately 91.9 ml/ml was also consistent with the know value of the potassium potential across the cell membrane. These results strongly suggested the potential of the dynamic pinhole SPECT as a tool for absolute quantitation of physiological parameters in small animals.

For the application of a kinetic model to PET data, it is necessary to obtain the arterial input function. Since arterial blood sampling is invasive and labor intensive, a method to evaluate the input function without arterial blood sampling is important. In case of the [/sup 15/O] water injection study, because of the noise in the time activity curve obtained from the PET reconstructed image round the carotid artery region, a model based evaluation method might be promised. In this study, a model function is composed or combination of blood time activity curve function and tissue time activity curve function which is generated from blood activity curve function. The present method was applied to 15 of dynamic PET scans or /sup 15/O water (10 normal subjects, 10 : Rest, and 5 : Diamox) for normal volunteers. The time activity curve obtained was fitted with the above model function. The shapes or input function obtained was in agreement with that by arterial blood sampling. The accuracy of height of the peak was 14 % and the accuracy of area under the curve was 10 %. This study supposed that present method could be used for direct extraction of the carotid artery input function from the dynamic PET image, and could be used in a quantitative CBF study using /sup 15/O water PET.

Radionuclide studies have gained wide acceptance in the evaluation of infants and children with gastroesophageal reflux (GER). For correct interpretation of scan results, knowledge of inter-observer and intra-observer variability and minimum detectable reflux volume is essential. In this study, we evaluated the methodological issues underlying the visual assessment of GER and time activity curve analysis. An in vitro model of stomach and oesophagus was established to determine the minimum detectable reflux by placing various volumes and concentrations representing the diluted activity in the stomach. In the clinical part 99 patients were imaged for 1 h after oral administration of 99mTc sulfur colloid. Eleven patients were excluded from the study either due to incomplete clinical data or suboptimal image quality. Frames of 16 s each, and time-activity curves which were generated after drawing regions of interest from the oesophagus, were read three times by an experienced nuclear medicine physician and a resident in training. On the phantom study, the concentration, volume and duration were the determining factor for the visualization of reflux. In the clinical part, the overall incidence of GER in 88 patients was 69%. The mean intra- and inter-observer reproducibility (kappa values) was 0.76 and 0.7065, respectively. Agreement was slightly higher in the analysis of time-activity curves (0.767 and 0.731). Our results indicate that GER may be reproducibly analysed on scintigraphy by the same and different observers with varying levels of training. Its visualization is associated with reflux duration, volume and dilution factor of radioactivity.

Quantitative measurements of cerebral blood flow (CBF) are performed in a volume imaging PET scanner by means of moderate activity infusions. In equilibrium infusions, activations are measured by scanning over 10 minutes with 16 minute activations. Typical measured whole brain CBF values are 37/spl plusmn/8 ml/min/dl, close to the value of 42 ml/min/dl reported by other groups using this method. For ramped infusions, scanning over 4 minutes with 5 minute activations results in whole brain CBFs of 49/spl plusmn/9 ml/min/dl, close to the Kety and Schmidt value of 50 ml/min/dl. Both equilibrium and ramped infusion methods have been used to study face and word memory in human subjects. Both methods were able to detect significant activations in regions implicated in human memory (amygdala and hippocampus). It is concluded that both accurate and precise quantitation of regional CBF (rCBF) is achieved using the methods described. In addition a simplified protocol for ramped infusion studies has been investigated. In this method the whole brain tissue time activity curve generated from dynamic scanning is replaced by an appropriately scaled camera coincidence countrate curve. The resulting whole brain CBF values are only 7% different from the dynamic scan results. Methods for obtaining the rCBF from the summed image and the resulting whole brain CBF are under investigation. >

The reconstruction of dynamic positron emission tomograph (PET) images is time consuming. Previous work to speed up the dynamic image reconstruction was based on low-order approximation using Karhunen-Loeve (KL) transform. Those KL transform basis vectors corresponding to the largest K eigenvalues were retained and then used in the reconstruction process. However, with this approach the kinetic characteristic (time activity curves) of weak signals, such as non-palpable tumors, may be lost or significantly changed in the reconstructed images. In this paper, a metric is found to select a subset of vectors from the KL transform basis, which relates directly to maximizing lesion-to-background ratio (signal-to-noise ratio). The results using computer simulation PET data show that by this approach the contrast of small lesion to the background can be objectively enhanced. The characteristic of the time activity curve in the lesions can also be approximately kept.

The kinetic analysis for dual tracer injection with 2-input compartment model is challenging in order to assess the two different functions In the same time and same situation. In this study, we investigated the possibility of kinetic analysis with two tracers, /sup 18/F-FDG and /sup 11/C-flumazenil (FMZ), by means of the computer simulation. The reliability of estimated parameters was Investigated for various injection protocols and noise levels. Simulated decaying tissue time activity curves were generated for various injection protocols with input function of FDG and FMZ and true k-values by using the 2-input 3-tissue compartment 5-parameter model, i.e. 2-tissue compartment 3-parameter for FDG and 1-tissue compartment 2-parameter for FMZ. The injection Interval of two tracers was changed from 0 to 20 minutes. The noise was generated depending on the total collected count and added each decaying tissue time activity curve. The rate constants for FDG and FMZ were estimated by nonlinear least square method. The reliability of parameter estimates was evaluated by mean absolute difference between true and estimated value of one thousand runs for each injection protocol and noise level. As a result, it was found that parameters were estimated most reliably when FDG was injected 15 minutes later than FMZ injection. In 5% last frame noise, the mean absolute difference between true and estimated value of Ki, reflecting the uptake of FDG, was about 8%, that of DV, distribution volume of FMZ, was 7%. The reliability was independent on the ratio of administration dose of FDG to that of FMZ. In the simulation study, the possibility of kinetic analysis for dual tracer injection was shown.

Although the parametric image (PI) of regional myocardial blood flow (rMBF) using H/sub 2//sup 15/O and PET would facilitate the numerical evaluation and the clinical visual interpretation of rMBF, low signal to noise ratio (SNR); of the time activity curve (TAC) of individual voxel in dynamic H/sub 2//sup 15/O PET image has made the composition of PI difficult to accomplish. The authors propose a method for PI of rMBF from H/sub 2//sup 15/O PET using factor analysis and cluster analysis. Factor analysis was performed to extract TACs of the right and left ventricular blood pool and their factor images. The blood pool activity was then subtracted from the original dynamic frames to remove the spillover contamination to myocardial tissue. Pure TACs in myocardial tissue were submitted to cluster analysis for PI of rMBF, which averaged voxels with the same shape TACs to increase SNR of PI and reduce calculation time. Parametric images showed good image quality and contrast in comparison to either the factor images of myocardial tissue or the subtracted imaged composed by subtracting the initial 30 seconds' images from the 2 minutes' ones. RMBF ranged 0.89-1.35 m/min/g at rest, and 1.16-3.85 at stress. Computation time was less than 1 minute on the workstation with 333 MHz CPU.

Publisher Summary Positron emission tomography (PET) has made it possible to detect accurately and noninvasively at the regional level, i.e., organ and tissue, the in vivo concentration of radiopharmaceuticals tagged with positron emitters. Image analysis can be made both qualitatively and quantitatively. For some clinical PET studies, a qualitative analysis is appropriate to answer biological questions, such as when the localisation of metabolic defects is the principal purpose of the study. However, quantitative information often is necessary and this requires interpretation of the PET tracer measurement with a mathematical model of the underlying physiological process. After presenting fundamentals on modelling strategies and measurement error, this chapter gives the quantitation of three physiological processes; glucose metabolism, blood flow, and ligand-receptor interaction.

The authors developed and tested a method for the noninvasive quantification of the cerebral metabolic rate for glucose (CMRglc) using positron emission tomography (PET),18F-fluoro-2-deoxyglucose, the Patlak method, and an image-derived input function. Dynamic PET data acquired 12 to 48 seconds after rapid tracer injection were summed to identify carotid artery regions of interest (ROIs). The input function then was generated from the carotid artery ROIs. To correct spillover, the early summed image was superimposed over the last PET frame, a tissue ROI was drawn around the carotid arteries, and a tissue time activity curve (TAC) was generated. Three venous samples were drawn from the tracer injection site at a later time and used for the spillover and partial volume correction by non-negative least squares method. Twenty-six patient data sets were studied. It was found that the image-derived input function was comparable in shape and magnitude to the one obtained by arterial blood sampling. Moreover, no significant difference was found between CMRglc estimated by the Patlak method using either the arterial blood sampling data or the image-derived input function.

We investigated the use of the Generalized Linear Least Squares (GLLS) method for fast estimation of myocardial blood flow (MBF) with N-13 ammonia Positron Emission Tomography (PET). GLLS was based on a high order integral equation converted from the state variable differential equations describing the kinetics of a PET tracer. Two error sources, spillover and the measurement noise, were studied. The estimation of the spillover coefficients between plasma time activity curve (TAC) and tissue TAC was incorporated into the GLLS. The GLLS procedure was modified accordingly. It was found, in computer simulation, that spillover correction incorporated GLLS provided as reliable MBF estimation as the model fitting method accounting for spillover. Since the linear kinetic model relating the plasma TAC to the tissue TAC was equivalent to the one relating the integral of plasma TAC (accumulated counts) to the integral of the tissue TAC, the GLLS method could be directly applied to the accumulated PET counts. It was found that the direct use of the accumulated counts reduced the random fluctuation observed in TAC data from PET images; and that this noise reduction significantly improved the accuracy of estimated MBF.

The quantitative analysis of dynamic positron emission tomography (PET) data to obtain estimates of tissue characteristics, such as blood flow, energy consumption, or receptor density, usually relies on fitting an appropriate kinetic model to the radiotracer time course data. This chapter presents a technique for constructing parametric images from three-dimensional dynamic PET studies. The approach is based on a mixture analysis model in which the time activity curve (TAC) at a given volume element (voxel) is expressed as a weighted sum of sub-TACs corresponding to homogeneous tissues represented there. Estimates of metabolic parameters at a voxel are defined as a weighted sum of the parameters associated with the individual sub-TACs. Segmentation plays a key role in the methodology. This chapter also presents an overview of the implementation of the approach illustrated by the application to a dual-tracer study designed to measure the local cerebral glucose lumped constant.

A more accurate quantitative method for the measurement of regional cerebral blood flow (rCBF) with the microsphere model and N-isopropyl-p-[123I]iodoamphetamine (123I-IMP) and ring-type single-photon emission computed tomography (SPECT) was developed. Continuous withdrawal of arterial blood was carried out for 5 minutes after the injection. Static SPECT data were acquired from 25 min to 55 min. To estimate reconstructed images at 5 min, total brain count collections and one minute SPECT studies were performed at 5, 20, and 60 min. Quantitative values for rCBF were calculated from short time SPECT images at 5 min (rCBF), static SPECT images corrected by total brain counts (rCBFCt) and those corrected by reconstructed counts on short time SPECT images (rCBFCb). Practically, rCBFCb is calculated by using reconstructed counts of regions of interest placed in the same position as static SPECT and short time SPECT at 5, 20, 60 min. Although there was good correlation between rCBF and rCBFCt (r = 0.69), rCBFCt tended to be underestimated in high flow areas and overestimated in low flow areas. A better correlation was observed between rCBF and rCBFCb (r = 0.92). The overestimation and underestimation observed in rCBFCt was considered to be due to the correction method with a total cerebral time activity curve, because the kinetic behavior of 123I-IMP was different in each region.

2020 Objectives Dynamic changes in tracer uptake in the whole heart may be useful as early predictors of cardiovascular disease or heart failure. The goal of this study was to demonstrate the feasibility of measuring changes in volumes-of-interest (VOI) activity using a DDGC. Previously we have developed the QPlanar method for estimating the activity organs or other VOI from planar projections. The method uses maximum-likelihood estimation techniques, and accurate models of the image formation to estimate the total activity in a set of 3D VOIs. In this study we adapted this methodology to extract dynamic information, in the form of the time activity curve for the myocardium and blood pool, from a conventional SPECT acquisition. In this study we used simulations to investigate the feasibility of estimating the time-activity curve (TAC) for the myocardium and blood pool. Methods In this study we modeled uptake in the heart based on literature[1] TAC of Tc-99m teboroxime. We modeled patient anatomy using the 3D XCAT phantom. Simulated data were generated using an analytic simulator that models attenuation, scatter and the collimator-detector response. We modeled acquisition using a two-camera system in a right angle configuration. We modeled a 12 minute acquisition with data acquired at 120 views over 360° using continuous rotation. We studied the effects of noise by estimating TACs for 30 noise realizations. To study the effects of nonuniform myocardial uptake, we modeled a 100% severity perfusion defect in 38% of the myocardium. Results TACs obtained of the heart and blood pool had an average (avg.) bias of 21% and 18% and avg. standard deviation of 26% and 25%, respectively. With the defect present the method underestimated the cardiac TAC by an avg. of 45.13%. We expect bias to be less severe with defect present in less than 25% of myocardium along with less than 100% severity. Conclusions The proposed method allows relatively simply extraction of dynamic information about the myocardium and blood pool with a conventional slow acquisition protocol

Positron Tomographs (PT) measure the concentration of a radioisotope in a tissue element of a given organ in vivo [1]. They produce a set of images where each voxel value represents the mean value, over a given time period, of the movement of the radioisotope in that volume element. If the process is repeated over several serial time periods, the kinetics of the radioisotope can be examined and the time activity curve (TAC) can be described with simple or complex model from which physiological parameters (such as blood flow, glucose metabolic rate, receptor concentrations or others) can be identified and estimated [2].

A quantitative model is presented which accurately reproduces the time activity curve of the human left ventricular blood pool. Four parameters receive numerical values and may be of clinical value.