Catheter guided ablation of cardiac arrhythmias is an effective and safe procedure for the treatment of most supraventricular and selected ventricular tachycardias. Because catheter manipulation is fluoroscopically guided, there is risk of radiation induced injury, especially during prolonged procedures. The Food and Drug Administration has recently issued a bulletin warning of the risks of acute skin injury occurring during fluoroscopically guided procedures that result in an exposure level exceeding 2 Gray units (Gy). This study was performed as an investigation into the risk of radiation induced skin injury during arrhythmia ablation procedures. The amount of radiation exposure for 500 patients who underwent ablation was calculated based upon fluoroscopy times and the entrance dose of radiation (0.02 Gy/min). The mean radiation exposure was 0.93 +/- 0.62 Gy. Although 5.6% of patients (n = 28) received enough radiation exposure to reach the threshold dose (2 Gy) for early transient erythema, no clinical manifestations of acute radiation induced skin injury were observed. No patients achieved the threshold dose for irreversible skin injury. Patients undergoing AV node ablation or modification received significantly less radiation (0.39 +/- 0.40 Gy and 0.79 +/- 0.44 Gy, respectively) than patients undergoing other ablation procedures (0.94-1.45 Gy, P < 0.05). There was no association between the magnitude of radiation exposure and the presence of underlying heart disease. Patients undergoing ablation of accessory pathways were exposed to more radiation if there was a right-sided pathway (1.69 +/- 0.93 Gy) compared to other sites (0.87-1.24 Gy, P < 0.05). This study demonstrates that the risk of significant radiation induced skin injury during arrhythmia ablation procedures is low provided that precautions are taken to minimize radiation exposure.

Radiofrequency catheter ablation is an effective alternative to medical therapy for patients with supraventricular arrhythmias. The purpose of this study was to determine the risks to the patient and to medical personnel due to radiation exposure from fluoroscopy during radiofrequency ablation of supraventricular tachycardia. One hundred eight consecutive patients with Wolff-Parkinson-White syndrome or atrioventricular nodal reentry who underwent the ablation procedure were studied. The ablation procedure was successful in 95% of the patients studied. Preexcitation or supraventricular tachycardia recurred in 5% of the patients during a mean follow-up of 9 +/- 4 months. The mean fluoroscopy time was 50 +/- 31 minutes. An anthropomorphic radiologic phantom was used to determine organ exposure and the effective dose equivalents for the patient and medical personnel. The patient's effective dose equivalent during a representative ablation procedure was 1.7 rems, which is comparable to other invasive cardiovascular procedures. The risk of inducing a fatal cancer from this exposure is 1 chance in 745, which is 1% of the spontaneous risk. The risk of a serious birth defect is 1 chance in 80,000, which is 0.1% of the current incidence of serious birth defects in the United States. The cardiologist who receives the highest exposure among medical personnel, would incur 1.8 mrems per case or 450 mrems per year if 250 procedures were performed. This exposure is 9% of the recommended annual limit. These results demonstrate the efficacy of radiofrequency energy ablation of supraventricular tachycardia and confirm that radiation exposure to patients and medical personnel is within established guidelines.

In preparation for measurement of regional cerebral oxygen metabolism by positron emission tomography, radiation absorbed dose estimates for 19 internal organs, blood, and total body were calculated for newborn infants following bolus intravenous administration of H2(15)O and brief inhalation of C15O and O15O. Cumulated activity for each radiopharmaceutical was calculated from a compartmental model based on the known biologic behavior of the compound. Values for mean absorbed dose/unit cumulated activity (S) for internal organs and total body were based on a newborn phantom. S was separately calculated for blood. Total radiopharmaceutical absorbed dose estimates necessary to measure cerebral oxygen metabolism in a 3.51-kg infant based on 0.7 mCi/kg H2(15)O and 1 mCi/kg C15O and O15O were determined to be 1.6 rad to the lung (maximum organ dose), 0.28 rad to the marrow, 0.46 rad to the gonads, and 0.22 rad to total body. These values are similar to those for current clinical nuclear medicine procedures employing 99mTc in newborn infants.

This study was designed to determine whether regional myocardial perfusion can be assessed quantitatively in vivo in dogs by administration of a freely diffusible tracer intravenously at an exponentially increasing-rate. Previously, we reported the mathematical basis of the approach and its use for assessment of global perfusion in isolated hearts. In this study, computer simulations demonstrated that inter-regional diffusion of tracer perturbs results by no more than 7 percent under worst case conditions. Regional myocardial blood flow assessed in open chest dogs with myocardial activity deternined by well counting by the exponential infusion method correlated closely to values obtained with radiolabeled microspheres (r = 0.986, n = 35 determinations). Thus, regional myocardial perfusion can be quantified with an infusion technique potentially applicable to the tomographic characterization of impaired perfusion in experimental animals and ultimately in patients with positron emission tomography.

A technique was developed and evaluated using the exponential infusion of positron-emitting diffusible tracers to quantitate myocardial perfusion. The approach employs a parameter that rapidly reaches a constant value as a function of tracer delivery rate, isotope decay constant, and the monotonically increasing tissue radioactivity. Isolated rabbit hearts with controlled flow were used to evaluate the approach, because tracer kinetics in such preparations mimic those in vivo. Accordingly, exponential infusions of H2 15O and [11C]butanol were administered to 25 isolated rabbit hearts perfused with Krebs-Henseleit solution (KH) alone or KH enriched with erythrocytes (KH-RBC, hematocrit = 40). With flow varied from 1.2 to 5 ml/g per min in eight KH hearts infused with H2 15O, actual and estimated flow correlated closely (r = 0.95, n = 52 determinations). For the KH-RBC hearts, flow was varied from 0.3 to 1.5 ml/g per min. Actual and estimated flow correlated significantly for both the 14 KH-RBC hearts infused with H2 15O (r = 0.90, n = 89 determinations) and the 3 KH-RBC hearts infused with [11C]butanol (r = 0.93, n = 13 determinations). In addition, the required exponentially increasing arterial tracer concentrations were shown to be attainable in vivo in dogs and rhesus monkeys after intravenous exponential administrations of tracer. The results suggest that the approach developed employing exponential tracer infusion permits accurate measurement of myocardial perfusion and that it should prove useful in the noninvasive measurement of regional myocardial perfusion in vivo by positron emission tomography.

The technique of positron emission tomography was used to measure cerebral blood volume (CBV) in 10 normal right‐handed human volunteers following inhalation of trace quantities of cyclotron‐produced, 11 C‐labeled carbon monoxide. In scans obtained 4 cm above the orbitomeatal line, CBV was 4.3 ml per 100 gm of tissue, whereas in scans obtained 8 cm above the orbitomeatal line, CBV was significantly less (3.3 ml per 100 gm; p < 0.001). This difference reflects the greater proportion of gray matter in the lower scan. Furthermore, the CBV was significantly larger ( p < 0.001) in the left cerebral hemisphere in the tomographic scans obtained 4 cm above the orbitomeatal line. These scans include the region of the superior surface of the temporal lobe (planum temporale), which is thought to be larger in individuals with left cerebral dominance for speech. This observation is the first in vivo demonstration of a structural correlate of a known functional difference in the cerebral hemispheres of man.

The brain vasculature, especially capillaries, may function in a very dynamic fashion under neuroendocrine control to regulate the internal environment of the brain. This is exemplified by new observations on the regulation of brain water permeability using the tracer H215O in vivo in adult rhesus monkeys. These studies reveal that brain water permeability, and hence brain water content and volume, are, at least in part, under the influence of the central noradrenergic system and centrally released vasopressin.

Radioiodinated soluble fibrin, a derivative of radioiodinated fibrinogen, has been investigated for thrombus localization. Soluble fibrin can be labeled with 123I as the radionuclide for imaging thrombi with a scintillation camera. Protein iodination grade 123I is produced by a distillation and extraction procedure from the product of the 121Sb (α, 2n) 123I reaction in the Washington University 54-in. cyclotron. Labeling with these 123I preparation is effected by the iodine monochloride method. Induced 4–6-hr-old femoral vein thrombi in dogs can be visualized beginning 2 hr after injection of 1 mCi of 123I-labeled soluble fibrin. This new radiopharmaceutical may be useful for imaging actively-propagating thrombi in patients, especially in areas of large blood pool. Its potential appears to be similar to that of 123I-labeled highly iodinated fibrinogen, another new thrombus imaging agent.

A series of experiments was undertaken to evaluate the response of a positron emission transverse tomograph (PETT) to measured radionuclide concentrations similar to those encountered in human studies. The correlation between the response of the imaging system (mean PETT number/min), and the concentration of the radioactivity producing the output data, was linear with a computed sensitivity of 2720 PETT number/min, per micronCi/ml, per picture element, for a radionuclide (100% beta+) contained in either of two phantoms and imaged with a reduction of 1.5 cm. It was concluded that the output data are essentially independent of the imaged object's physical dimensions for the range of 18-28-cm diam and faithfully reflect the regional radioactivity concentration within the object, provided valid attenuation correction is achieved and the sampled area is not compromised by the imaging system's limitations of spatial resolution.

Patients with dementia had significant decreases in cerebral blood flow and cerebral oxygen utilization and a mild, but not significant, increase in cerebral blood volume. These studies were not useful in distinguishing patients with cerebral atrophy from patients with normal pressure hydrocephalus, as similar changes in cerebral circulation and metabolism were seen in both groups. Changes in cerebral blood flow after acute decrease in the intracranial pressure also were not helpful in differentiating patients with normal pressure hydrocephalus from patients with cerebral atrophy.

Forty-five studies of regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF), and regional cerebral oxygen utilization (rCMRO2) were performed in 30 patients undergoing diagnostic cerebral angiography for evaluation of a subarachnoid hemorrhage due to a ruptured intracranial aneurysm. Tracer methods employing radioactive oxygen-15 were used to measure rCBV, rCBF, and rCMRO2. The patient studies were divided into groups based on their neurological status and the presence or absence of cerebral vasospasm. Subarachnoid hemorrhage, with and without vasospasm, produced significant decreases in CBF and CMRO2. In general, patients with more severe neurological deficits, and patients with more severe degrees of vasospasm, had a more marked depression of CBF and CMRO2. The most striking finding was a significant (p less than 0.001) increase in CBV (to 58% above normal) in patients with severe neurological deficits associated with severe cerebral vasospasm. This large increase suggests that cerebral vasospasm consists of constriction of the large, radiographically visible extraparenchymal vessels accompained by a massive dilation of intraparenchymal vessels.