Theoretical basis for controlling minimal tumor temperature duringinterstitial conductive heat therapy

This paper describes simulation of steady-state intratumoral temperatures achieved by a simple modality of local heat therapy: interstitial treatment with parallel arrays of warmed, conductive heating elements. During "conductive heating" power is directly deposited only in the interstitial probes. Adjacent tissue is warmed by heat conduction. Simulations of interstitial conductive heating involved solution of the bioheat transfer equation on a digital computer using a finite difference model of the treated tissue. The simulations suggest that when the complete temperature distributions for conductive interstitial hyperthermia are examined in detail, substantial uniformity of the temperature distributions is evident. Except for a thin sleeve of tissue surrounding each heating element, a broad, flat central valley of temperature elevation is achieved, with a well defined minimum temperature, very close to modal and median tissue temperatures. Because probes are inserted directly in tumor tissue, the thin sleeve of overheated tissue would not be expected to cause normal tissue complications. The temperature of the heated probes must be continuously controlled and increased in the face of increased blood flow in order to maintain minimum tumor temperature. However, correction for changes in blood flow is possible by adjusting probe temperature according to a feedback control scheme, in which power dissipation from each probe is the sensed input variable. Conductive interstitial heating with continually controlled probe temperature deserves investigation as a technique for local hyperthermia therapy.     

Non-penetrance and late appearance of polyps in families with familial adenomatous polyposis

One case of non-penetrance of the familial adenomatous polyposis (FAP) gene at 59 years of age and late onset of polyps on endoscopy and biopsy in this and two other families is described. Screening protocols should include dental screening as well as indirect ophthalmoscopy and endoscopy to detect minimal manifestations of the gene. In the absence of a specific DNA predictive test, bowel screening should continue well beyond 30 years of age.     

An inspiration-triggered delivery system for oxygen therapy via a nasal cannula

Therapy for severe chronic lung disease currently includes the administration of supplemental oxygen to prevent breathlessness and tissue hypoxia. Although effective, this therapy is unnecessarily costly, because oxygen is administered to the patient during expiration as well as inspiration. To eliminate this inefficiency, a delivery system that senses the inspiratory effort and delivers oxygen to the patient only during inspiration was developed. The 11 X 5 X 8-cm flow control unit attaches easily to a portable oxygen supply. The components of the system have an expected life of five years, and the 9-V battery provides power for about one month of use. Manual controls permit accommodation to the respiratory pattern of the patient. Preliminary evaluation of the system showed that its effectiveness in producing tissue oxygenation is similar to that of continuous oxygen systems. The system has potential applications in ambulatory oxygen therapy and in other clinical settings to improve the cost/benefit ratio of oxygen treatment.     

Preclinical ROC studies of digital stereomammography

Reports the diagnostic performance of observers in detecting abnormalities in computer-generated mammogram-like images. A mathematical model of the human breast is defined in which breast tissues are simulated by spheres of different sizes and densities. Images are generated by casting rays from a specified source, through the model, and onto an image plane. Observer performance when using two viewing modalities (stereo versus mono) is compared. In the stereo viewing mode, images are presented to the observer (wearing liquid-crystal display glasses), such that the left eye sees the left image only and the right eye sees the right image only. In this way, the images can be fused by the observer to obtain a sense of depth. In the mono viewing mode, identical images are presented to the left and right eyes so that no binocular disparities will be produced by the images. Observer response data are evaluated using receiver operating characteristic (ROC) analysis to characterize any difference in detectability of abnormalities (in either the density or the arrangement of simulated tissue densities) using the two viewing modes. The authors' experimental results indicate the clear superiority of stereo viewing for detection of arrangement abnormalities. For detection of density abnormalities, the performance of the two viewing modes is similar. These preliminary results suggest that stereomammography may permit easier detection of certain tissue abnormalities, perhaps providing a route to earlier tumor detection in cases of breast cancer.     

Direct activation of cardiac adrenergic nerve endings by defibrillator shocks

Defibrillator shocks ranging in intensity from three to nine times current threshold were delivered to four isolated, metabolically supported, beating canine hearts. The shocks produced an immediate, current-dependent depression of left ventricular isovolumic systolic pressure. This depression was transient, reproducible, and was followed by a transient overshoot in ventricular systolic pressure. Then 1 mg propranolol hydrochloride in 1 ml H2O was injected into the coronary arterial supply of the isolated heart, and the shocks were repeated. The magnitude of the immediate cardiac depression after shock was unchanged; however, the time required for full recovery of left ventricular systolic pressure to a pre-shock control value was prolonged. In addition, the transient overshoot in ventricular systolic pressure seen in the untreated state was absent. These results are consistent with the hypothesis that defibrillatory shocks produce a direct activation of cardiac adrenergic nerves, which aid in recovery of ventricular contractility following defibrillator shocks.     

Multiresolution detection of spiculated lesions in digitalmammograms

We present a novel multiresolution scheme for the detection of spiculated lesions in digital mammograms. First, a multiresolution representation of the original mammogram is obtained using a linear phase nonseparable two-dimensional (2-D) wavelet transform. A set of features is then extracted at each resolution in the wavelet pyramid for every pixel. This approach addresses the difficulty of predetermining the neighborhood size for feature extraction to characterize objects that may appear in different sizes. Detection is performed from the coarsest resolution to the finest resolution using a binary tree classifier. This top-down approach requires less computation by starting with the least amount of data and propagating detection results to finer resolutions. Experimental results using the MIAS image database have shown that this algorithm is capable of detecting spiculated lesions of very different sizes at low false positive rates     

Use of combined systemic hypothermia and local heat treatment to enhance temperature differences between tumor and normal tissues

The feasibility of combining local heat treatment with whole-body hypothermia in an effort to improve therapeutic gain was assessed. Superficial, nonperfused phantom tumors were fashioned in eight anesthetized mongrel dogs by transplantation of the spleen from the abdomen to a subcutaneous site on the hindlimb. After pretreatment of the animal with the vasodilator hydralazine (0.5 mg/kg, IV) to enhance normal tissue perfusion, the spleen implant was heated with a 2450-MHz microwave diathermy apparatus, first with the animal's core body temperature in the normal range (39 degrees C) and then after the animal had been packed in ice to reduce core temperature to 30 degrees C. Applied power density and temperatures in both the phantom tumor and underlying muscle tissue were recorded during brief interruptions of diathermy until steady-state temperatures had been achieved. Under normothermic conditions with time-averaged applied power of 0.038 W/ml to phantom tumor and 0.014 W/ml to underlying muscle, tumor temperature rose to 45.9 +/- 1.8 degree C, while muscle temperature remained at 40.5 +/- 0.7 degree C. During whole-body hypothermia applied power could be increased to 0.114 W/ml in phantom tumor and to 0.025 W/ml in muscle. Muscle temperature rose only to 33.8 +/- 1.6 degree C, while that of the nonperfused phantom tumor rose to 53.6 +/- 4.3 degrees C with systemic hypothermia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potassium efflux from myocardial cells induced by defibrillator shock

A transient, dose-dependent cardiac depression was produced by defibrillator shocks in an isolated, working canine heart preparation perfused with oxygenated arterial blood from a support dog. Accompanying this depression was an efflux of potassium (K+), forced out of the myocardial cells by the passage of defibrillating current. The transient increase in extracellular K+ concentration was recorded graphically in the venous outflow. It was found that 5-msec rectangular wave shocks, from three to ten times defibrillatory current threshold, released dose-related pulses of K+. It is concluded that because K+ is a myocardial depressant, at least part of the myocardial depression after defibrillation is caused by the release of K+ from the myocardial cells.