A single-cell pedigree analysis of alternative stochastic lymphocyte fates.

In contrast to most stimulated lymphocytes, B cells exposed to Toll-like receptor 9 ligands are nonself-adherent, allowing individual cells and families to be followed in vitro for up to 5 days. These B cells undergo phases typical of an adaptive response, dividing up to 6 times before losing the impetus for further growth and division and eventually dying by apoptosis. Using long-term microscopic imaging, accurate histories of individual lymphocyte fates were collected. Quantitative analysis of family relationships revealed that times to divide of siblings were strongly related but these correlations were progressively lost through consecutive divisions. A weaker, but significant, correlation was also found for death times among siblings. Division cessation is characterized by a loss of cell growth and the division in which this occurs is strongly inherited from the original founder cell and is related to the size this cell reaches before its first division. Thus, simple division-based dilution of factors synthesized during the first division may control the maximum division reached by stimulated cells. The stochastic distributions of times to divide, times to die, and divisions reached are also measured. Together, these results highlight the internal cellular mechanisms that control immune responses and provide a foundation for the development of new mathematical models that are correct at both single-cell and population levels.

Automated and semi-automated cell tracking: addressing portability challenges.

Cell tracking is a key task in the high-throughput quantitative study of important biological processes, such as immune system regulation and neurogenesis. Variability in cell density and dynamics in different videos, hampers portability of existing trackers across videos. We address these potability challenges in order to develop a portable cell tracking algorithm. Our algorithm can handle noise in cell segmentation as well as divisions and deaths of cells. We also propose a parameter-free variation of our tracker. In the tracker, we employ a novel method for recovering the distribution of cell displacements. Further, we present a mathematically justified procedure for determining the gating distance in relation to tracking performance. For the range of real videos tested, our tracker correctly recovers on average 96% of cell moves, and outperforms an advanced probabilistic tracker when the cell detection quality is high. The scalability of our tracker was tested on synthetic videos with up to 200 cells per frame. For more challenging tracking conditions, we propose a novel semi-automated framework that can increase the ratio of correctly recovered tracks by 12%, through selective manual inspection of only 10% of all frames in a video.

The effect of correlations on the population dynamics of lymphocytes.

Recent studies of the population dynamics of a system of lymphocytes in an in vitro immune response have reported strong correlations in cell division times, both between parents and their progeny, and between those of sibling cells. The data also show a high level of correlation in the ultimate number of divisions achieved by cells within the same clone. Such correlations are often ignored in mathematical models of cell dynamics as they violate a standard assumption in the theory of branching processes, that of the statistical independence of cells. In this article we present a model in which these correlations can be incorporated, and have used this model to study the effect of these correlations on the population dynamics of a system of cells. We found that correlation in the division times between parents and their progeny can alter the mean population size of clones within the system, while all of the correlations can affect the variance in the sizes of different clones. The model was then applied to experimental data obtained from time-lapse video microscopy of a system of CpG stimulated B lymphocytes and it was found that inclusion of the correct correlation structure is necessary to accurately reproduce the observed population dynamics. We conclude that correlations in the dynamics of cells within an ensemble will affect the population dynamics of the system, and the effects will become more pronounced as the number of divisions increases.

Regional variability in age-related loss of neurons from the primary visual cortex and medial prefrontal cortex of male and female rats.

During aging, changes in the structure of the cerebral cortex of the rat have been seen, but potential changes in neuron number remain largely unexplored. In the present study, stereological methods were used to examine neuron number in the medial prefrontal cortex and primary visual cortex of young adult (85-90 days of age) and aged (19-22 months old) male and female rats in order to investigate any age-related losses. Possible sex differences in aging were also examined since sexually dimorphic patterns of aging have been seen in other measures. An age-related loss of neurons (18-20%), which was mirrored in volume losses, was found to occur in the primary visual cortex in both sexes in all layers except IV. Males, but not females, also lost neurons (15%) from layer V/VI of the ventral medial prefrontal cortex and showed an overall decrease in volume of this region. In contrast, dorsal medial prefrontal cortex showed no age-related changes. The effects of aging clearly differ among regions of the rat brain and to some degree, between the sexes.

Metabolism in immunoreactive parathyroid hormone in the dog. The role of the kidney and the effects of chronic renal disease.

The role of the kidney in the metabolism of parathyroid hormone (PTH) was examined in the dog. Studies were performed in awake normal and uremic dogs after administration of bovine parathyroid hormone (b-PTH) or synthetic amino terminal tetratricontapeptide of b-PTH (syn b-PTH 1-34). The renal clearance of immunoreactive PTH was determined from the product of renal plasma flow and the percent extraction of PTH immunoreactivity by the kidney. Blood levels of circulating immunoreactive PTH were determined by radioimmunoassay. The normal dog kidney extracted 20 plus or minus 1% of the immunoreactive b-PTH delivered to it, and renal clearance (RC) of immunoreactivity was 60 ml/min. When RC was compared to an estimate of total metabolic clearance (MCR) of immunoreactivity, it accounted for 61% of the total. Both MCR and RC were markedly decreased in dogs with chronic renal disease. However, the percent extraction of immunoreactive PTH was unchanged in chronic renal disease, and the observed decrease in RC was due to changes in renal plasma flow. The largest portion of the reduction in total MCR was accounted for by the decrease in RC, and there was no compensation for the decrease in RC by extrarenal sites of PTH metabolism.

Neuron number decreases in the rat ventral, but not dorsal, medial prefrontal cortex between adolescence and adulthood.

Neuroimaging studies have established that there are losses in the volume of gray matter in certain cortical regions between adolescence and adulthood, with changes in the prefrontal cortex being particularly dramatic. Previous work from our laboratory has demonstrated that cell death can occur as late as the fourth postnatal week in the rat cerebral cortex. The present study examined the possibility that neuronal loss may occur between adolescence and adulthood in the rat prefrontal cortex. Rats of both sexes were examined during adolescence (at day 35) and young adulthood (at day 90). The volume, neuronal number, and glial number of the medial prefrontal cortex (mPFC) were quantified using unbiased stereological techniques. Neurons were lost from the ventral, but not dorsal, mPFC between adolescence and adulthood, suggesting a late wave of apoptosis that was region-specific. This was accompanied by a decrease in the volume of the female ventral mPFC. In contrast to neuron number, the number of glial cells was stable in the ventral mPFC and increased between adolescence and adulthood in the dorsal mPFC. Sex-specific developmental changes in neuron number, glial number, and volume resulted in sex differences in adults that were not seen during adolescence. The loss of neurons at this time may make the peri-adolescent prefrontal cortex particularly susceptible to the influence of environmental factors.

Comparison of gramicidin A and gramicidin M channel conductance dispersities.

To explore the possible role of Trp side chains in gramicidin channel conductance dispersity, we studied the dispersity of gramicidin M (gM), a gramicidin variant in which all four tryptophan residues are replaced with phenylalanine residues, and its enantiomer, gramicidin M(-) (gM(-)), and compared them to that of gramicidin A (gA). The conductances of highly purified gM and gM(-) were studied in alkali metal solutions at a variety of concentrations and voltages, in seven different types of lipid, and in the presence of detergent. Like gA channels, the most common gM channel conductance forms a narrow band. However, unlike gA channels, where the remaining 5-30% of channel conductances are broadly distributed below (and slightly above) the main band, in gM there is a narrow secondary band with <50% of the main peak conductance. This secondary peak was prominent in NaCl and KCl, but significantly diminished in CsCl and RbCl. Under some conditions, minor components can be observed with conductances yet lower than the secondary peak. Interconversions between the primary conductance state and these yet lower conductance states were observed. The current-voltage relations for both primary and secondary gM channel types have about the same curvature. The mean lifetime of the secondary channel type is below one third that of the primary type. The variants represent state deviations in the peptide or adjacent lipid structure.

Blood-to-brain glucose transport and cerebral glucose metabolism are not reduced in poorly controlled type 1 diabetes.

To test the hypothesis that blood-to-brain glucose transport is reduced in poorly controlled type 1 diabetes, we studied seven patients with a mean (+/- SD) HbA1c level of 10.1 +/- 1.2% and nine nondiabetic subjects during hyperinsulinemic, mildly hypoglycemic (approximately 3.6 mmol/l, approximately 65 mg/dl) glucose clamps. Blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves--the latter determined by positron emission tomography (PET)--after intravenous injection of [1-(11)C]glucose using a model that includes a fourth rate constant to account for regional egress of 11C metabolites. Cerebral blood flow and cerebral blood volume were determined with intravenous H2(15)O and inhaled C(15)O, respectively, also by PET. At plateau plasma glucose concentrations of 3.6 +/- 0.0 and 3.7 +/- 0.1 mmol/l, rates of blood-to-brain glucose transport were similar in the two groups (23.7 +/- 2.2 and 21.6 +/- 2.9 micromol x 100 g(-1) x min(-1), P = 0.569, in the control subjects and the patients, respectively). There were also no differences in the rates of cerebral glucose metabolism (16.8 +/- 0.8 and 16.3 +/- 1.2 micromol x 100 g(-1) x min(-1), P = 0.693, respectively). Plasma epinephrine (1,380 +/- 340 vs. 450 +/- 170 pmol/l, P = 0.0440) and glucagon (26 +/- 5 vs. 12 +/- 1 pmol/l, P = 0.0300) responses to mild hypoglycemia were reduced in the patients with type 1 diabetes. We conclude that neither blood-to-brain glucose transport nor cerebral glucose metabolism is measurably reduced in people with poorly controlled type 1 diabetes.

Blood-to-brain glucose transport, cerebral glucose metabolism, and cerebral blood flow are not increased after hypoglycemia.

Recent antecedent hypoglycemia has been found to shift glycemic thresholds for autonomic (including adrenomedullary epinephrine), symptomatic, and other responses to subsequent hypoglycemia to lower plasma glucose concentrations. This change in threshold is the basis of the clinical syndromes of hypoglycemia unawareness and, in part, defective glucose counterregulation and the unifying concept of hypoglycemia-associated autonomic failure in type 1 diabetes. We tested in healthy young adults the hypothesis that recent antecedent hypoglycemia increases blood-to-brain glucose transport, a plausible mechanism of this phenomenon. Eight subjects were studied after euglycemia, and nine were studied after approximately 24 h of interprandial hypoglycemia ( approximately 55 mg/dl, approximately 3.0 mmol/l). The latter were shown to have reduced plasma epinephrine (P = 0.009), neurogenic symptoms (P = 0.009), and other responses to subsequent hypoglycemia. Global bihemispheric blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves-the latter determined by positron emission tomography (PET)-after intravenous injection of [1-(11)C]glucose at clamped plasma glucose concentrations of 65 mg/dl (3.6 mmol/l). For these calculations, a model was used that includes a fourth rate constant to account for egress of [(11)C] metabolites. Cerebral blood flow was measured with intravenous [(15)O]water using PET. After euglycemia and after hypoglycemia, rates of blood-to-brain glucose transport (24.6 +/- 2.3 and 22.4 +/- 2.4 micromol. 100 g(-1). min(-1), respectively), cerebral glucose metabolism (16.8 +/- 0.9 and 15.9 +/- 0.9 micromol. 100 g(-1). min(-1), respectively) and cerebral blood flow (56.8 +/- 3.9 and 53.3 +/- 4.4 ml. 100 g(-1). min(-1), respectively) were virtually identical. These data do not support the hypothesis that recent antecedent hypoglycemia increases blood-to-brain glucose transport during subsequent hypoglycemia. They do not exclude regional increments in blood-to-brain glucose transport. Alternatively, the fundamental alteration might lie beyond the blood-brain barrier.

Noninvasive quantitation of myocardial blood flow in human subjects with oxygen-15-labeled water and positron emission tomography.

Noninvasive measurement of myocardial blood flow in absolute terms (i.e., milliliters per gram per min) has been difficult to accomplish despite the intrinsically quantitative power of positron emission tomography because of the nonphysiologic nature of tracers that have been employed conventionally as well as the limited spatial resolution of currently available instruments. It was previously demonstrated that myocardial blood flow in animals can be quantitated accurately with the diffusible tracer oxygen-15-labeled water (H2(15)O) when the arterial input function and myocardial radiotracer concentration were measured directly. To extend the approach for completely noninvasive measurement of blood flow, a parameter estimation procedure was developed whereby effects of limited tomographic spatial resolution and cardiac motion were compensated for within the operational flow model. In validation studies in 18 dogs, myocardial blood flow measured with positron emission tomography after intravenously administered H2(15)O correlated closely with flow measured with concomitantly administered radiolabeled microspheres over the range of 0.29 to 5.04 ml/g per min (r = 0.95). Although regional ischemia was clearly identifiable tomographically, absolute flow could not be determined accurately in ischemic regions in four dogs because of poor count statistics related to wall thinning. Subsequently, myocardial blood flow was measured in 11 normal human subjects. Flow was homogeneous throughout the myocardium, averaged 0.90 +/- 0.22 ml/g per min at rest and increased to 3.55 +/- 1.15 ml/g per min after intravenous administration of dipyridamole. Therefore, positron emission tomography with H2 15O and the approach developed permits noninvasive measurement of myocardial blood flow in absolute terms in humans and should facilitate objective assessment of interventions designed to enhance nutritive perfusion.

The use of aspirin for primary and secondary prevention in venous thromboembolism and other cardiovascular disorders.

Cardiovascular disease (CVD) includes a number of conditions such as myocardial infarction, coronary heart disease, stroke, and venous thromboembolism. CVD is a leading health problem worldwide and a major cause of mortality, morbidity, and disability; it is also associated with high healthcare costs. The incidence of CVD is predicted to increase in the forthcoming years, and thus it is crucial that physicians are aware of the benefits and limitations of the available therapies to ensure patients receive optimized treatment. Current clinical practice guidelines provide recommendations on the use of anticoagulants and antiplatelets for both the prevention and treatment of CVD. Aspirin is the most studied antiplatelet agent in this context. The benefits of aspirin are well documented and supported by data from robust clinical trials for CVD conditions, such as acute coronary syndrome and stroke prevention in patients with atrial fibrillation. However, the clinical benefits of aspirin are less clear for other conditions, namely for primary prevention of venous thromboembolism after major orthopaedic surgery, particularly in comparison with newer drugs such as the direct oral anticoagulants. This article provides an outline of the current guidelines and a critical assessment of the efficacy and safety data supporting the recommendations for the use of aspirin in the treatment and prevention of venous thromboembolism and other cardiovascular disorders.

Tracer-kinetic models for measuring cerebral blood flow using externally detected radiotracers.

All tracer-kinetic models currently employed with positron-emission tomography (PET) are based on compartmental assumptions. Our first indication that a compartmental model might suffer from severe limitations in certain circumstances when used with PET occurred when we implemented the Kety tissue-autoradiography technique for measuring CBF and observed that the resulting CBF estimates, rather than remaining constant (to within predictable statistical uncertainty) as expected, fell with increasing scan duration T when T greater than 1 min. After ruling out other explanations, we concluded that a one-compartment model does not possess sufficient realism for adequately describing the movement of labeled water in brain. This article recounts our search for more realistic substitute models. We give our derivations and results for the residue-detection impulse responses for unit capillary-tissue systems of our two candidate distributed-parameter models. In a sequence of trials beginning with the simplest, we tested four progressively more detailed candidate models against data from appropriate residue-detection experiments. In these, we generated high-temporal-resolution counting-rate data reflecting the history of radiolabeled-water uptake and washout in the brains of rhesus monkeys. We describe our treatment of the data to yield model-independent empirical values of CBF and of other parameters. By substituting these into our trial-model functions, we were able to make direct comparisons of the model predictions with the experimental dynamic counting-rate histories, confirming that our reservations concerning the one-compartment model were well founded and obliging us to reject two others. We conclude that a two-barrier distributed-parameter model has the potential of serving as a substitute for the Kety model in PET measurements of CBF in patients, especially when scan durations for T greater than 1 min are desired.

In vivo kinetics of [18F](N-methyl)benperidol: a novel PET tracer for assessment of dopaminergic D2-like receptor binding.

A novel D2-like receptor-binding radioligand, [18F](N-methyl)benperidol ([18F]NMB), was evaluated via positron emission tomographic (PET) imaging studies of baboons. [18F]NMB rapidly localized in vivo within dopaminergic receptor-rich cerebral tissues, and striatum-to-cerebellum ratios as high as 35 were achieved after 3 hours. Pretreatment of an animal with unlabeled receptor-specific antagonists before injection of [18F]NMB confirmed that the radioligand bound specifically to central D2-like receptors in vivo, and not to S2- or D1-like receptors. Unlabeled eticlopride displaced striatal [18F]NMB in vivo, showing that D2-like binding is reversible. Receptor-binding by the radioligand was resistant to competitive displacement by synaptic dopamine, as illustrated by the lack of effect of intravenous d-amphetamine on the in vivo localization of [18F]NMB. Studies involving sequential intravenous administration of [18F]NMB, d-amphetamine, and eticlopride show that the radioligand does not undergo agonist-mediated internalization with subsequent trapping. The feasibility of applying a three-compartment non-steady state model for quantification of [18F]NMB receptor binding was demonstrated. These in vivo characteristics give [18F]NMB distinct advantages over the PET radiopharmaceuticals currently used for clinical investigation of D2-like receptor binding.

Cerebral glucose transport and metabolism in preterm human infants.

Few data regarding early developmental changes in cerebral (blood-to-brain) glucose transport (CTXglc) and CMRglc are available for humans. We measured CBF, CTXglc, and CMRglc with positron emission tomography at 4 to 7 days of life in six preterm human infants whose estimated gestational age was 25 to 34 weeks. The Michaelis-Menten constants Kt and Tmax were estimated from CTXglc and the calculated cerebral capillary plasma glucose concentration. Mean CMRglc was 8.8 mumol 100 g-1 min-1. The CMRglc did not correlate with plasma glucose concentration (r = .315, P = .543), whereas CTXglc showed a significant correlation with plasma glucose concentration (r = .836, P = .038). Estimation of the Michaelis-Menten constants from the best fit to the measured data produced values of Kt = 6.0 mumol mL-1 and Tmax = 32.6 mumol 100 g-1 min-1. These values for Kt in the developing human brain are similar to those that have been reported for the mature brain of adolescent and adult humans and adult nonhuman primates, indicating the affinity of the glucose transport protein for D-glucose is similar. However, Tmax is approximately one third to one half of the comparable values for mature brain, indicating a reduced number of available luminal transporters.

Strategies for in vivo measurement of receptor binding using positron emission tomography.

Dopaminergic ligands labeled with positron-emitting radionuclides have been synthesized for quantitative evaluation of dopaminergic binding in vivo. Two different methods, the explicit method and an operationally simplified ratio method, have been proposed for analysis of these positron emission tomographic (PET) data. The basis for both methods is the same three-compartment model. The two methods differ in the assumptions necessary for practical implementation. We have compared these two approaches using PET data obtained in our laboratory. Sequential scans and serial arterial blood samples from a baboon following intravenous injection of [18F]spiroperidol were collected. Application of the two methods to the same data yielded different values for corresponding parameters. Values calculated by the ratio method for the specific rate constant describing receptor binding varied depending upon the time after tracer injection, thus demonstrating an internal inconsistency in this approach. Tracer metabolism markedly affected the binding measurements calculated with either method and thus cannot be ignored. Our results indicate that the adoption of simplifying assumptions for operational convenience can lead to substantial errors and must be done with caution. Alternatively, we present simple new analytical solutions of the tracer conservation equations describing the complete, unsimplified three-compartment model that vastly reduce the computations necessary to implement the explicit method.

Measurement of regional cerebral blood flow with positron emission tomography: a comparison of [15O]water to [11C]butanol with distributed-parameter and compartmental models.

To further our understanding of the best way to measure regional CBF with positron emission tomography (PET), we directly compared two candidate tracers ([15O]water and [11C]butanol, administered intravenously) and two popular implementations of the one-compartment (1C) model: the autoradiographic implementation representing a single PET measurement of tissue radioactivity over 1 min and a dynamic implementation representing a sequence of measurements of tissue radioactivity over 200 s. We also examined the feasibility of implementing a more realistic, and thus more complex, distributed-parameter (DP) model by assigning fixed values for all of its parameters other than CBF and tracer volume of distribution (Vd), a requirement imposed by the low temporal resolution and statistical quality of PET data. The studies were performed in three normal adult human subjects during paired rest and visual stimulation. In each subject seven regions of interest (ROIs) were selected, one of which was the primary visual cortex. The corresponding ROI were anatomically equivalent in the three subjects. Regional CBF, Vd, tracer arrival delay, and dispersion were estimated for the dynamic data curves. A total of 252 parameter sets were estimated. With [11C]butanol both implementations of the 1C model provided similar results (r = 0.97). Flows estimated using the 1C models were lower (p < 0.01) with [15O]water than with [11C]butanol. In comparison with the 1C model, the constrained version of the DP used in these studies performed inadequately, overestimating high flow and underestimating low flow with both tracers, possibly as the result of the necessity of assigning fixed values for all of its parameters other than CBF and Vd.

Sex differences in mouse cortical thickness are independent of the complement of sex chromosomes.

Although the morphology of the cerebral cortex is known to be sexually dimorphic in several species, to date this difference has not been investigated in mice. The present study is the first to report that the mouse cerebral cortex is thicker in males than in females. We further asked if this sex difference is the result of gonadal hormones, or alternatively is induced by a direct effect of genes encoded on the sex chromosomes. The traditional view of mammalian neural sexual differentiation is that androgens or their metabolites act during early development to masculinize the brain, whereas a feminine brain develops in the relative absence of sex steroids. We used mice in which the testis determination gene Sry was inherited independently from the rest of the Y chromosome to produce XX animals that possessed either ovaries or testes, and XY animals that possessed either testes or ovaries. Thus, the design allowed assessment of the role of sex chromosome genes, independent of gonadal hormones, in the ontogeny of sex differences in the mouse cerebral cortex. When a sex difference was present, mice possessing testes were invariably masculine in the morphology of the cerebral cortex, independent of the complement of their sex chromosomes (XX vs. XY), and mice with ovaries always displayed the feminine phenotype. These data suggest that sex differences in cortical thickness are under the control of gonadal steroids and not sex chromosomal complement. However, it is unclear whether it is the presence of testicular secretions or the absence of ovarian hormones that is responsible for the thicker male cerebral cortex.

Brain blood flow measured with intravenous H2(15)O. I. Theory and error analysis.

The tissue autoradiographic method for the measurement of regional cerebral blood flow (rCBF) in animals was adapted for use with positron emission tomography (PET). Because of the limited spatial resolution of PET, a region of interest will contain a mix of gray and white matter, inhomogeneous in flow and in tracer partition coefficient (lambda). The resultant error in rCBF, however, is less than 4%. Although the tissue autoradiographic method requires a monotonically increasing input function to ensure a unique solution for flow, the PET adaptation does not, because of an additional integration in the operational equation. Simulation showed that the model is accurate in the presence of ischemia or hyperemia of the gray matter. Inaccuracy in timing of the arterial input function will result in large errors in rCBF measurement. Propagation of errors in measurement of tissue activity is largely independent of flow, reflecting the nearly linear flow compared with activity relationship.

The effects of regional pulmonary blood flow on protein flux measurements with PET.

We used PET to evaluate whether changes in regional pulmonary blood flow (PBF) or plasma volume (PV) affect calculations of the pulmonary transcapillary escape rate (PTCER) for 68Ga-labeled transferrin. We reduced PBF in five dogs by inflating a right atrial balloon. Regional PBF decreased 25% to 174 +/- 40 ml/min/100 ml lung without a change in PV or PTCER. In eight other dogs, we decreased PBF and PV via controlled arterial hemorrhage. PBF decreased 45% to 110 +/- 33 ml/min/100 ml lung and PV decreased 22% without a change in PTCER. We also used a series of computer simulations to evaluate the effect of even greater reductions in regional PBF on PTCER calculations. These simulations showed, in support of the experimental data, that if PBF was greater than 40 ml/min/100 ml lung, PTCER could be accurately measured. However, below this level, PV was increasingly under-estimated and PTCER overestimated. The results indicate the sensitivity of the PTCER calculation to errors in the PV measurement, especially in regions of markedly reduced regional PBF.

Quantitation of myocardial fatty acid metabolism using PET.

UNLABELLED: Abnormalities of fatty acid metabolism in the heart presage contractile dysfunction and arrhythmias. This study was performed to determine whether myocardial fatty acid metabolism could be quantified noninvasively using PET and 1-(11)C-palmitate. METHODS: Anesthetized dogs were studied during control conditions; during administration of dobutamine; after oxfenicine; and during infusion of glucose. Dynamic PET data after administration of 1-(11)C-palmitate were fitted to a four-compartment mathematical model. RESULTS: Modeled rates of palmitate utilization correlated closely with directly measured myocardial palmitate and total long-chain fatty acid utilization (r = 0.93 and 0.96, respectively, p < 0.001 for each) over a wide range of arterial fatty acid levels and altered patterns of myocardial substrate use (fatty acid extraction fraction ranging from 1% to 56%, glucose extraction fraction from 1% to 16% and myocardial fatty acid utilization from 1 to 484 nmole/g/ min). The percent of fatty acid undergoing oxidation could also be measured. CONCLUSION: The results demonstrate the ability to quantify myocardial fatty acid utilization with PET. The approach is readily applicable for the determination of fatty acid metabolism noninvasively in patients.