Deep-seated Tissues Research Articles

Focal beam distortion and treatment planning in abdominal focused ultrasound surgery

Recent clinical trials show promising results in using MRI and MRI-based thermometry to guide focused ultrasound surgery to treat uterine fibroids. During treatment, large variation in the focal temperature distribution has been observed. It is possible that some of this variation is due to abdominal tissue inhomogeneity, which might be causing focal beam distortion, and might largely decrease the focusing ability in deep-seated tissues. The purpose of this study was to numerically demonstrate this effect and also show the feasibility of restoring the focal beam patterns by employing the phase correction procedure for phased arrays. Abdominal MR data from four uterine fibroid patients were obtained to reconstruct the three-dimensional meshes of interfaces used in simulations, and one patient was selected to perform the analysis of key parameters in focused ultrasound surgery. Results show that, without phase correction, the focused beam can be severely distorted while using a frequency above 1 MHz or delivering ring-shape focal patterns. Different focal positions at the same depth may require a different power to induce the same ultrasonic intensity level (up to 179% among the different focal patterns). After adding a phase correction procedure, the distorted focal beams can be restored, and the peak intensity can be largely recovered (up to 85% among the different focal patterns). This study may offer important implications and information for treatment planning toward optimizing focused ultrasound surgery in uterine fibroid or other abdominal tumor treatments.

Development and clinical application of near-infrared surgical microscope: preliminary report.

Visualization of near-infrared fluorescence through a surgical microscope can provide intraoperative information about deep-seated tissues. We studied the possibility of taking a near-infrared image through a surgical microscope after intravenous injection of indocyanine green (ICG). The surgical microscopes we used were Zeiss models OPMI MD and OPMI CS-NC. We used a halogen lamp as a light source, a band pass filter of 760 - 810 nm as an excitation filter, a laser light of 800 nm as an external light source, and a band pass filter of 820 - 920 nm as a barrier filter. Near-infrared fluorescence of vessels on the brain surface and of the dural sinus was visualized through the dura mater after intravenous injection of 25 mg ICG using a Hitachi KP-160 camera. Near-infrared fluorescence of vessels on the brain surface was observed through the dura mater. Venous images were clearer than were arterial ones. The dural sinus and the bridging veins were also clearly visualized. These results suggest that a clinical application of near-infrared fluorescence microscopy is possible. However, a stronger fluorescence emitted from ICG will be necessary for such a microscope to have practical use.

Fine-needle aspiration with flow cytometric immunophenotyping for primary diagnosis of intra-abdominal lymphomas.

Cytomorphology in conjunction with immunophenotypic characterization is becoming increasingly used for the primary diagnosis of non-Hodgkin's lymphomas (NHL). This combination is especially advantageous for the diagnosis of intra-abdominal and intrathoracic lymphomas, since unlike superficial lesions, open biopsy of deep-seated tissues is more invasive and more costly, and is associated with a higher risk. We report the cytologic and immunophenotypic features of intra-abdominal NHL obtained by fine-needle aspiration (FNA). Twenty-two cases of intra-abdominal lesions obtained by image-guided FNA where flow cytometry was also performed were reviewed. Of the 22 studied cases, 7 were classified as large-cell lymphoma, 5 as follicular center-cell lymphoma, 2 as small noncleaved-cell lymphoma, 2 as lymphoplasmacytoid lymphoma, one as small lymphocytic lymphoma, and one as marginal-zone lymphoma. In the remaining 4 cases where the immunophenotypic pattern was not definitive, the cytomorphologic features were of small cleaved cells in 3 cases and of mixed small cleaved and large cells in one case. We successfully classified 9 of the 10 patients on whom histologic confirmation was obtained. The successful primary classification of most intra-abdominal non-Hodgkin's lymphomas can be done with a combination of cytology and flow cytometry, and this can be the initial approach in patients with deep-seated lesions. Diagn. Cytopathol. 1999;21:98-104.

New Frontiers in Medical Device Technology

Microwave Balloon Angioplasty Catheter Ablation for the Treatment of Cardiac Arrhythmias The Efficacy of Transurethral Thermal Ablation in the Management of Benign Prostatic Hyperplasia Localized Heating of Deep-Seated Tissues Using Microwave Balloon Catheters Microwave Surgery Contemporary Ophthalmic Lasers Advanced Technologies in Coronary Angioplasty: Lasers and Stents Advances in Magnetic Resonance Imaging Medical Ultrasonic Imaging - State-of-the-Art and Future Thermography - Radiometric Sensing in Medicine.

Practical induction heating coil designs for clinical hyperthermia with ferromagnetic implants.

Interstitial techniques for hyperthermia therapy of cancer continue to evolve in response to requirements for better localization and control over heating of deep seated tissues. Magnetic induction heating of ferromagnetic implants is one of several available techniques for producing interstitial hyperthermia, using thermal conduction to redistribute heat within an array of controlled temperature "hot sources." This report describes seven induction heating coil designs that can be used for producing strong magnetic fields around ferromagnetic seed implants located in different sites in the body. The effect of coil design on the extent and uniformity of the magnetic field is characterized, and appropriate electrostatic shield designs for minimizing electric field coupling to the patient are described. Advantages and disadvantages of each coil type are discussed in terms of the radiated fields, coil efficiency, and ease of use, and appropriate applications are given for each design. This armamentarium of induction coils provides the ability to customize magnetic field distributions for improved coupling of energy into ferromagnetic implant arrays located at any depth or orientation in the body. Proper selection of heating coil configuration should simplify patient setup, improve the safety of patient treatments, and pave the way for future applications of interstitial heating in sites that were previously untreatable.

Thermal distribution studies of helical coil microwave antennas for interstitial hyperthermia

An implantable 915 MHz helical coil antenna was developed for improved localization and control of interstitial microwave hyperthermia. The radiating element consisted of a fine wire coil wound back over the inner conductor of a miniature semi-rigid coaxial cable in place of the terminal portion of outer conductor. The power deposition profiles from single helical coil antennas were studied both in homogeneous phantom and in muscle tissue in vivo and compared to those of single half-wavelength linear dipole antennas. The effects of variable coil length, turn density, and antenna insertion depth in tissue were characterized. The helical coil antennas produced a well-localized heating pattern with a sharp falloff of temperature in both directions axially from the coil element. One of the best heating patterns was obtained with a 35 turn, 35 mm long helical coil element which was separated from the antenna feedline outer conductor by a 1 mm gap (HCS-35(1)/36). This antenna showed a marked shift of the effectively heated volume toward the antenna tip and essentially no dependence of the heating pattern on insertion depth. In contrast, the axial power deposition profiles of dipole antennas were strongly affected by insertion depth and exhibited an inadequately heated area at the antenna tip even with 1 4 − 3 4 wavelength insertion. Thermal distribution studies showed that the single helical coil microwave antenna provided more predictable, well-localized heating of deep-seated tissues, with minimal requirement for over-implanting of the treatment volume.

On minimisation of toxicity to skin during capacitive radio-frequency hyperthermia.

Common techniques to induce tissue hyperthermia (HT) with radio-frequency (RF) currents are either capacitive or inductive in type (Cheung, 1982; Cosset et al, 1983). An advantage with RF capacitive HT is the possibility of heating deep-seated tissues (Cheung, 1982; U et al, 1984). However, during capacitive heating the higher resistivity of subcutaneous tissues results in excessive heating, which leads to skin and fat burns and induration (Arcangeli et al, 1983; Perez et al, 1983; Hiraoka et al, 1984; Oleson et al, 1984; U et al, 1984). To prevent the direct contact of the electrode with the skin, electrodes are enclosed in bolus bags through which cooled fluids such as saline (Brezovich et al, 1981; Cheung, 1982) or deionised water (Hiraoka et al, 1984; Prionas & Hahn, 1984; U et al, 1984) are circulated. Brezovich et al (1981) have shown that the skin burns during RF capacitive heating could be reduced by using a saline bolus of tissue-equivalent conductivity and Griffiths et al (1984) have reported th...

Development of a family of RF helical coil applicators which produce transversely uniform axially distributed heating in cylindrical fat-muscle phantoms.

Uniform transverse heating, without excessive surface heating, in phantoms which simulate human limbs or trunks has long been sought after as a precursor for predictable hyperthermia treatment of deep-seated cancerous tissues. A family of helical coils developed at the National Center for Devices and Radiological Health has induced transversely uniform axially distributed heating in the muscle portion of simulated fat-muscle, cylindrical arm- and thigh-sized phantoms without excessively heating the simulated fat. The final design parameters for the coils were derived using different sized coil/phantom combinations and electric (E)-and magnetic (H)-field strength measurement scans. Transverse heating patterns, in the form of thermographic pictures, will be the principal format for presentation of the experimental data in this paper. Independent nonperturbing thermometry data are also included to enhance the accuracy of the thermographic results obtained.

On the optimization of local hyperthermy in tumors based on a new radiofrequency procedure. Local hyperthermy of large body areas using the CMT selectotherm method.

A new radiofrequency procedure, i.c., the CMT Selectotherm technique, permits to convey large heat quantities per volume unit also to deep-seated tumor tissues without causing thermal lesions in healthy tissues near or at the body surface. The improved spatial homogeneity of energy supply attainable by this method is demonstrated by measurements at a gelatine phantom and, in particular, by in vivo measurements on pigs. The appliability of local hyperthermy to tumors localized in different parts of the body is substantially improved (a) by the principle of superimposing local hyperthermy on an elevated temperature level of metabolically induced whole-body hyperthermy (CMT-spontaneous hyperthermy at 40 degrees C) and (b) by the principle of selective increasing the thermal sensitivity of tumor tissues by decreasing the pH in these areas (the CMT main step). It is shown that the temperature dose T. deltat necessary for the selective occlusion of the vasculature in tumor tissues can be obtained by the CMT Selectotherm process also in deep-seated tumors. This process is part of the 1977 CMT concept. The fundamentals of optimizing local hyperthermy with consideration of heat dissipation from the tissue by heat conduction and convection via the blood stream are demonstrated. Temperature profiles are calculated for some practice-relevant, typical examples (inner and outer parts of sphero-symmetrically shaped tumors). Finally, in vivo measurements and calculations on the time course of temperature under certain conditions and for different tissue layers are discussed.

Comparative studies of meat. VIII. The percentage of fat in the fatty and muscular tissues of steers and the iodine number of the extracted fat, as affected by breed and level of nutrition

1. An investigation has been carried out concerning the percentage of fat in the subcutaneous and intermuscular fatty tissues and in the muscular tissues, and the iodine number of the extracted fat from eight anatomical joints (foreshin, neck, shoulder, thorax, loin, pelvis, leg and hindshin) and from the perinephric fatty tissue and psoas muscles of the carcasses from twenty-four animals. The animals were from three breeds (Hereford, Dairy Shorthorn and Friesian) and were on four levels of nutrition—high-high and medium-high, and high-medium and medium-medium. The first two groups—finished on concentrates—were younger than the second two groups—finished on grass.2. Using an analysis of variance for the resultant data for percentage of fat and iodine number, it was found that breed had affected the percentage of fat in the tissues of the various joints significantly—on the average the order was Shorthorn (highest), Hereford and Friesian (lowest). This result could be predicted from the fact that this was the order of fatness of the carcasses (as measured by the percentage of fatty tissue in the carcass—see Callow, 1961).3. The data for iodine number showed no significant effect for breed in either the subcutaneous or intermuscular tissues. The significant effect of breed in the case of muscle could be attributed to significant differences in the overall level of fatness (see Callow, 1961) of the carcasses of the three breeds.4. A good correlation existed between the average percentage of fat in a joint and the average iodine number of fat extracted when the data for various joints was used to calculate straight lines of best fit. (In the case of muscular tissue, it was necessary to use the inverse of the percentage of fat to calculate the average—because the relation between the percentage of fat in muscular tissue and its iodine number is a rectangular hyperbola.)5. Using such lines of best fit, it was possible to show that certain joints had tissues which gave abnormal values for iodine number. Thus, deepseated tissues, like psoas muscle and kidney fat, had unexpectedly low values, whilst tissues from the hindshin had unexpectedly high values. This was attributed to the effect of local temperature—a high local temperature in the body giving a lower iodine number and a low temperature a higher iodine number than would otherwise be expected. The special case of subcutaneous fat from the thorax—with a higher iodine number than expected—is explained by the presence of brisket fat (which has a high iodine number).6. The data were used graphically to show the effect of growth gradients, thus the average percentage of fat in all the tissues is lowest in fore- and hindshins and highest in thorax (muscular and intermuscular tissues) and in the pelvis (subcutaneous tissue). Similar effects, but in the reverse direction, were shown by average values for iodine numbers.7. There were systematic differences in the percentage of fat in the subcutaneous and intermuscular tissues of joints and in the iodine number of the extracted fat. These too showed marked growth gradients. Although the percentage of fat in the intermuscular tissue was greater than that in the subcutaneous tissue in the fore- and hindshins, it was less in the thorax, loin, pelvis and leg. In spite of this, the iodine number of the subcutaneous fat was always higher than that of the intermuscular fat. This is attributed to the former being a colder tissue than the latter.8. It was shown that the relation between iodine number and percentage of fat in the various joints was different for the animals finished on grass (highmoderate and moderate-moderate levels of nutrition) as compared with those finished on concentrates (high-high and moderate-high levels). This was attributed to the rate of fattening being greater in the second case and to this giving rise to lower iodine numbers.9. Beyond this effect of rate of fattening, no reason could be found for the fact that the general level of iodine numbers showed variation from animal to animal.10. The extreme variation in percentage of fat in the tissues was (a) muscular tissue from 1·3 to 14·5%, (b) intermuscular tissue from 29·5 to 82·7%, and (c) subcutaneous tissue from 25·2 to 89·8%. For iodine number the variation was (a) 50·0 to 73·9, (b) 42·9 to 67·9 and (c) 46·3 to 67·9 It is thus clear that beef can be a very variable foodstuff.