Continuous Thermometry Research Articles

Changes in the Structure and Mechanical Properties of the Bone after Puncture Cryoablation: Experimental Study

Purpose of the study — to evaluate possible impact of cryoablation on a healthy bone and to identify probable causes of postoperative fractures.Materials and Methods. The authors performed cryoablation of the femur in the experiment on 8 mature rabbits of Soviet Chinchilla (SC) breed with a follow up for up to two months. Anitrogenous cryoprobe of 1.5 mm in diameter was introduced into the femur through a perforation hole. The bone was completely frozen up to -180°С in two cycles with continuous thermometry. Pathomorfological examinations were performed after 7 and 55 days along with assessment of bone hardness. Preparation of material stipulated sawing the bone at the fracture site along the bone axis. One half-bone was used for histological examination, and another one — for measuring mechanical properties by local pressing of a diamond indenter onto the bone at certain applied force. The distance between measurement points along the bone was 250 μm. Statistical processing included variance significance analysis using t-test.Results. The authors reported bone fractures at the site of cryodestruction in all animals in one week after the procedure. Statistical analysis of the measurements and histological examination demonstrated that freezing of the entire bone diameter up to -180°С results in its complete destruction. Strength reduction around the fracture site corresponded to the temperature distribution area in the range from -9ºС to -15ºС. However, areas of cooling below -40ºС exhibited some bone segments with normal hardness. Mosaic pattern of strength reduction is explained by microcirculation disorders. Histology confirmed thrombosis of intraosseous blood vessels in the area of cryotherapy. The first focal signs of osteomalacia emerged by the end of the first week after cryoablation. Subsequently, the bone preserved its regenerative properties, but by the end of the second month after the procedure the histogenesis was still not completed and the bone did not regain its strength.Conclusion. The authors believe that a limited number of cases, the specific features of the angioarchitecture of animal bones and their ability to produce a heavy periosteal response do not allow to apply obtained quantitative outcomes of the present study to clinical situations. However, complete freezing of the entire bone diameter inevitably results in fracture formation.

Continuous Temperature Measurement of Liquid Iron and Slag Tapped from a Blast Furnace

Temperature measurements of liquid pig iron coming out of a blast furnace are essential for estimating the thermal condition in the hearth. The temperature is generally monitored by a disposable thermocouple on a runner. This paper proposes radiometric temperature measurement that targets an iron-slag-mixed stream in front of a taphole. It enables non-contact continuous thermometry. Liquid iron and slag are spatially separated on a thermal image obtained by a CCD camera with a high-speed electronic shutter. Molten iron temperature is calculated from the iron radiance detected automatically by means of histogram processing of the thermal image. Regarding optically semitransparent molten slag, its radiance varies as a function of the thickness. Slag temperature is determined from the highest radiance, presuming that the emittance of sufficiently thick slag converges on a constant. The authors performed an on-site test at a blast furnace in ordinary operation. It was confirmed that both iron and slag temperatures were continuously monitored. The temperature data obtained from the test showed findings such as unsteady temperature difference between the two liquids and discontinuous temperature fluctuation. This imaging thermometry technique is expected to be used in a new sensor for blast furnace operation.

Two-wavelength differential thermometry for microscopic extended source

Sample temperature may theoretically be determined if we know or measure four quantities (two radiances at two specific wavelengths). We performed differential, continuous two-wavelength thermometry on a micro-surface element of the coiled coil filament used in tungsten lamp with a spectrometer. Results indicate that differential, continuous thermometry using a spectrometer measures temperature distribution along a short line. This method significantly enhances the capability of this established technique to new applications.

Magnetic resonance temperature imaging for guidance of thermotherapy.

Continuous thermometry during a hyperthermic procedure may help to correct for local differences in heat conduction and energy absorption, and thus allow optimization of the thermal therapy. Noninvasive, three-dimensional mapping of temperature changes is feasible with magnetic resonance (MR) and may be based on the relaxation time T(1), the diffusion coefficient (D), or proton resonance frequency (PRF) of tissue water. The use of temperature-sensitive contrast agents and proton spectroscopic imaging can provide absolute temperature measurements. The principles and performance of these methods are reviewed in this paper. The excellent linearity and near-independence with respect to tissue type, together with good temperature sensitivity, make PRF-based temperature MRI the preferred choice for many applications at mid to high field strength (>/= 1 T). The PRF methods employ radiofrequency spoiled gradient-echo imaging methods. A standard deviation of less than 1 degrees C, for a temporal resolution below 1 second and a spatial resolution of about 2 mm, is feasible for a single slice for immobile tissues. Corrections should be made for temperature-induced susceptibility effects in the PRF method. If spin-echo methods are preferred, for example when field homogeneity is poor due to small ferromagnetic parts in the needle, the D- and T(1)-based methods may give better results. The sensitivity of the D method is higher that that of the T(1) methods provided that motion artifacts are avoided and the trace of D is evaluated. Fat suppression is necessary for most tissues when T(1), D, or PRF methods are employed. The latter three methods require excellent registration to correct for displacements between scans.

A thermocouple system for continuous thermometry in radiofrequency hyperthermia.

When treating cancer with hyperthermia, the most widely-used method of temperature monitoring is by thermocouples implanted in the tissue. However, since thermocouples are metallic they can interact with the applied electromagnetic field, giving rise to large errors in the indicated temperatures (Gammampila et al, 1981; Hahn, 1982). Our investigations show that when using capacitive coupling to apply RF power to the patient, the temperature errors can be reduced to an acceptably low level by suitable encapsulation of the thermocouple wires and in-line filtering. Thermocouples were constructed by twisting together the ends of copper and constantan wires 50 μm in diameter and securing with soft solder. Probes were formed by inserting the “hot” junctions into lengths of nylon tubing (1 mm diameter, 0.18 mm wall thickness), Araldite resin being injected into the end of each probe to envelop and anchor the junction.

The thermal effect of the superhigh frequency electromagnetic field

Rectal and subcutaneous temperatures were studied in experiments on 170 animals—dogs, cats, rabbits, rats, and frogs—by the method of continuous thermometry in super-high-frequency electromagnetic fields of different intensities. In addition, thermometry was carried out in muscles and brain of rabbits. The survival time of various animals was determined, as well as the temperature increase. The characteristics of heating and cooling were investigated. The temperature curves followed the law of ascending and descending exponentials in heating and cooling, respectively. The heating effect was greatest in the subcutaneous tissue, less in the brain and deep in the muscles of the thigh, and even less in the rectum. The thermal effect, in the super-high-frequency field, depends on the energy flux, the exposure time, and the size and species of the animal. The lower limit of the “thermal conditions” which cause the death of small animals, including cats (lethal effect), is 0.05 watt/cm2. The lower limit of the “thermal conditions”., at which there is no heating effect on tissues, is 0.01 watt/cm2.