PubMed Health⌕ Search

Biomedical subjects

T K Natarajan

Publications and source records attributed to T K Natarajan.

At least 19 recordsLinked to original sources
PubMed1991

Reduced left ventricular cavitary activity ("black hole sign") in thallium-201 SPECT perfusion images of anteroapical transmural myocardial infarction.

Apparently reduced left ventricular (LV) cavitary thallium activity in both planar and tomographic perfusion images has been previously observed by these and other investigators. With single-photon emission computerized tomography, we have clinically noted that this "black hole sign" was associated with an aneurysm in the setting of a transmural anterior or anteroapical perfusion defect. We have now prospectively studied the etiology and predictive value of this sign in 84 consecutive patients with an anterior, anteroapical transmural perfusion defect. Of the 84 patients, 49 had both LV aneurysm (confirmed by contrast ventriculography, echocardiography or gated blood pool studies) and a black hole sign. Only 1 patient with an aneurysm did not have the black hole sign, and 2 without aneurysm did. Thus, it is concluded that this sign is highly accurate in diagnosing LV aneurysm. Because thallium-201 single-photon emission computerized tomography imaging is often performed as one of the first diagnostic tests soon after myocardial infarction, this has important clinical management implications.

Adult↗
PubMed1991

Imaging histamine H1 receptors in the living human brain with carbon-11-pyrilamine.

The brain distribution and kinetics of the H1 receptor antagonist, carbon-11-pyrilamine (11C-pyrilamine) were examined in vivo in two baboons and one human by positron emission tomography. After i.v. administration of the tracer, brain activity peaked within 20 min after injection and subsequently decreased, reflecting reversible binding to the receptor. Pretreatment with 1 mg/kg diphenhydramine reduced the brain activity at 70 min by 33%, 29%, 26%, and 23% of the control values in frontal cortex, temporal cortex, hippocampus, and cerebellum, respectively. Coinjection of 1 and 5 mg/kg cold pyrilamine reduced the activity at 70 min by 40%, 36%, 34%, and 30% in frontal, temporal, hippocampus and cerebellum, respectively. The in vivo specific binding to the H1 receptors in different brain regions at 70 min after injection correlated with the in vitro H1 histamine receptors distribution in human brain tissue obtained at autopsy, with high values in the frontal and temporal cortex and low values in cerebellum and brain stem. In the healthy human volunteer study, the value of washout of radioactivity increased by about 50% after injection of 0.7 mg/kg diphenhydramine.

Adult↗
PubMed1987

Immediate effect of expiratory loading on left ventricular stroke volume.

While the steady-state effects of positive pleural pressure on the circulation have been extensively studied, less is known about the immediate effects of positive intrathoracic pressure on cardiac dynamics. Therefore, we performed electrocardiographically gated radionuclide ventriculography with a respiratory gating technique in nine healthy subjects during quiet breathing and during expiration against a 24 cm H2O expiratory threshold load. During expiration, respiratory loading caused an increase in stroke counts by 29.4% (p less than .001) due to an increase in end-diastolic counts of 26.1% (p less than .001). End-systolic counts also rose 18.8% (p less than .05). The ejection fraction did not change significantly. These findings indicate that the increase in left ventricular stroke volume that occurs during the first 1 or 2 beats of a loaded expiration is due to an increase in left ventricular filling and not to augmentation of left ventricular ejection. This immediate increase in pulmonary venous return may reflect increased distensibility of the left ventricle due to decreased filling of the right ventricle.

Adolescent↗
PubMed1986

Simplified detection system for neuroreceptor studies in the human brain.

A simple, inexpensive dual-detector system has been developed for measurement of positronemitting receptor-binding drugs in the human brain. This high efficiency coincidence counting system requires that only a few hundred microcuries of labeled drug be administered to the subject, thereby allowing for multiple studies without an excessive radiation dose. Measurement of the binding of [11C]carfentanil, a high affinity synthetic opiate, to opiate receptors in the presence and in the absence of a competitive opiate antagonist indicates the potential utility of this system for estimating different degrees of receptor occupation in the human brain.

Binding, Competitive↗
PubMed1985

Right ventricular ejection fraction measured by first-pass intravenous krypton-81m: reproducibility and comparison with technetium-99m.

Study of the effects of various diseases and therapeutic manipulation of pulmonary vascular resistance on the right ventricle has been restricted by methodologic limitations. The radioactive gas in solution, krypton-81m was used to study the right ventricle and the technique was compared with a technetium-99m method. In 22 subjects, first-pass krypton-81m right ventricular ejection fraction, acquired both in list mode and electrocardiogram-gated frame mode, correlated well (r = 0.81 and 0.86, respectively, p less than 0.01) with that determined by technetium-99m first-pass studies over a broad range of ventricular function. The reproducibility of the technique was excellent (r = 0.84 and 0.95 for each acquisition mode, respectively). Krypton-81m first-pass studies provide accurate and reproducible estimates of right ventricular function. Use of krypton allows multiple measurements, with or without perturbations, over a short period of time.

Heart Ventricles↗
PubMed1977

Evaluation of indium-111 as a new high photon yield gamma-emitting "physiological" platelet label.

In order to evaluate indium-111 (111In) as a "physiological" platelet label, rabbit platelets were labeled in vitro with 111In-8-hydroxyquinoline. The in vivo behavior of 111In labeled platelets was then compared with that of chromium-51 51Cr) labeled platelets in the rabbit. Several important features were evident. First, unlike 51Cr, reasonable platelet labeling efficiency could be achieved with 111In, even when the platelets were suspended in small amounts of autologous plasma. Second, the initial recovery of platelets at 20 minutes after infusion was significantly higher for the 111In labeled platelets than for 51Cr labeled platelets, providing the platelets were suspended and "washed" in plasma. Third, the mean survival time of 111In labeled platelets, as estimated using four different mathematical models, was comparable with that of 51Cr platelets. Finally, the high photon yield of gamma emitting 111In, unlike 51Cr, permits quantitative gamma camera imaging of the in vivo distribution of labeled platelets. Thus, this nuclide possesses advantages as a platelet label that will foster statistically more accurate kinetic research as well as quantitative in vivo distribution studies in humans.

Animals↗
PubMed1976

The nuclear stethoscope: a simple device for generation of left ventricular volume curves.

Initial evaluation has begun of a system for displaying left ventricular time-activity curves, relating the intraventricular content of radioactivity with the cardiac cycle as determined by the patient's electrocardiogram. Major problems include proper positioning of the detector, correction for background radioactivity outside the ventricle and calibration of the device to permit conversion of measurement of radioactivity to measurement of ventricular volumes.

Cardiac Volume↗
PubMed1975

A test for patency of the cystic duct in acute cholecystitis.

A procedure was devised to quickly and reliably determine the patency of the cystic duct in patients suspected of having acute cholecystitis. First the gallbladder was stimulated to empty by a cholecystokinin injection. Thirty minutes later a radiolabeled biliary marker, either 150 muCi 131-I rose bengal or 2 mCi 99-mTc dihydrothioctic acid, was injected, and the accumulation of radioactivity in the liver and gallbladder regions was monitored by external gamma emission imaging and recording devices. The images of diagnostic importance were obtained between 60 and 90 minutes after injection of the tracer. Thirty-nine patients with acute abdominal pain were studied. Ten patients who had acute cholecystitis failed to show gallbladder accumulation of radioactivity, reflecting the cystic duct obstruction that initiates this disease. Twenty-nine patients having a variety of other diseases all showed gallbladder accumulation of activity, indicating in each patient that the cystic duct was patent. No significant adverse effects were noted. We conclude that the procedure is a useful adjunct to the clinical and roentgenographic evaluation of patients with acute abdominal pain.

Acute Disease↗