Предложен и исследован алгоритм восстановления методом акустотермометрии пространственного температурного распределения, меняющегося во времени, основанный на априорной информации о том, что изменение температуры подчиняется уравнению теплопроводности. Определялись два параметра распределения: источник и коэффициент температуропроводности. Восстановление проведено на основе экспериментальных данных, полученных при нагреве модельного объекта (говяжьей печени). Получение температурного распределения занимает 10 с, и (при погрешности измерения 0.1 K) в процессе восстановления достигается точность около 0.5 K, что полностью отвечает медицинским требованиям.

An acoustothermometric algorithm for reconstruction of the time-varying spatial temperature distribution is proposed and studied. The algorithm is based on the following a priory information: temperature variations is described by the heat conduction equation. Two distribution parameters are determined: the source and the temperature conductivity coefficient. Reconstruction is carried out on the basis of experimental data obtained when the model object (beef liver) is heated up. Obtaining these data requires 10 seconds (for a measurement error of about 0.1 K). In the reconstruction process, an error of about 0.5 K, which completely meets the medical requirements, is attained.

Non-invasive deep brain acoustic thermometry is carried out for two patients at Burdenko Neurosurgery Institute. This method is based on the measurements of the own thermal acoustic radiation of the investigated object. These two patients have got the brain injury. Some of their skull bones are absent. Infrared thermometry was also used to measure the surface temperature of the forehead skin. On the basis of the experimental data the temperatures deep within the brain were reconstructed. The values for the two patients are equal to 37.3 ± 0.7 and 37.0 ± 0.3°C.

Проведена неинвазивная глубинная акустическая термометрия мозга двух пациентов НИИ нейрохирургии им. акад. Н.Н. Бурденко РАМН, у которых частично отсутствовали кости черепа. Совместно с акустотермографией использовали и ИК-тепловидение для измерения температуры поверхности кожи. На основе экспериментальных данных восстановлена глубинная температура мозга: 37,3 ± 0,7 и 37,0 ± 0,3°С.

In an experiment, the deep temperature, which changed with time, was recovered for a model object, bovine liver. The liver was heated for 6 min by laser radiation (810 nm), transmitted via a light guide to a depth of 1 cm. During heating and subsequent cooling, the deep temperature was measured by acoustic thermography. For independent control, we used three electronic telemeters, the indications of which were also subsequently recovered. Deep temperature was recovered using a neural network with a time delay. During the last 2 min of heating, the mean square error of recovery for an averaging time of 50 s did not exceed 0.5°C. Such a result makes it possible to use this method for solving a number of medical problems.

The influence of blood flow and thermal output on temperature changes in the human forearm under physical pressure is studied by acoustic thermometry. Compression of the shoulder with a tourniquet decreases blood flow, which make it possible to evaluate the thermal output characteristics only. In calculating the depth temperature of the forearm, the thermal conductivity equation was used and blood flow and additional thermal output sources were taken into account. According to the calculations in which the experimental data were used, the peak depth temperature of the forearm at rest is 36°C. Due to thermal output alone (without blood flow), physical pressure increases this temperature to 37°C, and when both factors are considered, the temperature rises to 38°C. The experiments in question have allowed us to test acoustic thermographic method on subjects, which is an important step in adopting acoustic thermography in clinical practice.

Представлены результаты акустотермометрического контроля локальной гипотермии и гипертермии кисти человека. Испытуемые на несколько минут опускали руки в холодную и горячую воду. Измерения теплового акустического излучения проводили двумя датчиками со стороны ладони и с тыльной стороны кисти. Были восстановлены профили глубинной температуры в кисти. Косвенная оценка погрешности восстановления составила 0.6°С, что приемлемо для медицинских приложений. При гипертермии руку держали в течение двух минут в воде с максимальной температурой 44°С. При этом глубинная температура составила 35.4 ± 0.6°С. При гипотермии руку держали в течение пятнадцати минут в воде с температурой 17.8°С. При этом глубинная температура снизилась с 26 до 24°С. Использование плоской приемной решетки из четырех датчиков позволило провести динамическое картирование акустояркостной температуры кисти.

Методом акустотермометрии изучено влияние кровотока и теплопродукции на изменение температуры предплечья человека при физической нагрузке. Пережимание плеча жгутом приводит к снижению кровотока, что позволяет оценить параметры исключительно теплопродукции. При расчетах глубинной температуры предплечья использовалось уравнение теплопроводности с учетом кровотока и дополнительных источников теплопродукции. Расчеты с использованием экспериментально полученных данных показали, что максимум глубинной температуры предплечья в покое составляет 36°С. Физическая нагрузка только за счет теплопродукции (без кровотока) повышает эту температуру до 37°С, а с учетом и теплопродукции, и кровотока – до 38°С. Проведенные эксперименты позволили отработать методику акустотермографических измерений на испытуемых, что является важным этапом доведения метода акустотермометрии до клинической практики.

The results of an acoustothermometric study of the human hand under local hyperthermia and hypothermia are presented. Individuals under testing plunged their hands in hot or cold water for several minutes. Thermal acoustic radiation was detected by two sensors placed near the palm and near the backside of the tested hand. The internal temperature profiles of the hand were reconstructed. The indirect estimate of the reconstruction error was 0.6°C, which is acceptable for medical applications. Hyperthermia was achieved by placing the hand in water with a maximal temperature of 44°C for 2 min. In this case, the internal temperature was 35.4 ± 0.6°C. Hypothermia was achieved by placing the hand in water with a temperature of 17.8°C for 15 min. In this case, the internal temperature decreased from 26 to 24°C. The use of a four-sensor planar receiving array allowed dynamic mapping of the acoustic brightness temperature of the hand.

В эксперименте восстановлена меняющаяся во времени глубинная температура модельного объекта: говяжьей печени. Печень в течение 6 минут нагревали лазерным излучением (810 нм), передаваемым с помощью световода на глубину 1 см. Во время нагрева и последующего охлаждения глубинная температура измерялась методом акустотермографии. Для независимого контроля использовали три электронных термометра, показания которых в последующем и восстанавливали. Восстановление глубинной температуры проводилось с помощью нейронной сети с задержкой. В течение последних двух минут нагрева среднеквадратическая погрешность восстановления при времени усреднения 50 с не превышала 0.5°C. Такой результат позволяет использовать предлагаемый метод для решения ряда медицинских задач.

In a model experiment using the acousto-thermographic method, deep temperature profiles varying in time are recovered. In the recovery algorithm, we used a priori information in the form of a requirement that the calculated temperature must satisfy the heat conduction equation. The problem is reduced to determining two parameters: the initial temperature and the temperature conductivity coefficient of the object under consideration (the plasticine band). During the experiment, there was independent inspection using electronic thermometers mounted inside the plasticine. The error in the temperature conductivity coefficient was about 17% and the error in initial temperature determination was less than one degree. Such recovery results allow application of this approach to solving a number of medical problems. It is experimentally proved that acoustic irregularities influence the acousto-thermometric results as well. It is shown that in the chosen scheme of experiment (which corresponds to measurements of human muscle tissue), this influence can be neglected.

Экспериментально проверены корреляционный и некорреляционный способы приема теплового акустического излучения. Для корреляционного приема предложена формула расчета распределения температуры объекта по измеренным кросс-корреляционным функциям давления. Некорреляционные измерения, проведенные с использованием двух перпендикулярных решеток, состоящих из семи датчиков каждая, позволили определить параметры трехмерного температурного распределения, время измерения составило 10 с.

Two- and three-dimensional dynamic acoustothermography is carried out in model experiments. The temperature of the model plasticine objects was determined from the measurements of their thermal acoustic radiation in the course of their heating and cooling. The measurements were performed with the use of a planar array of 14 acoustothermometers and two planar arrays perpendicular to each other with 7 acoustothermometers in each of them. The results of measurements were used to plot a dynamic map of the temperature of acoustic brightness and to reconstruct the dynamics of variations in the parameters of the temperature distribution: the spatial coordinates of the heated region, its characteristic size and, maximal temperature. The duration of one measurement cycle was 10 s, the error in determining the position of the center and the size of the heated region did not exceed 1 mm, and the accuracy of the temperature’s calculation was about 1 degree. The results of the study may be used for controlling the temperature in the course of medical procedures that include heating of internal tissues in human patients.

In Central Clinic of RAS the acoustothermometrical measurements were carried out during laser hyperthemia of mammary and thyroid glands for heating control. Seven patients were investigated. The mammary and thyroid glands were heated 3 and 4 times, correspodently. One or two acoustothermometers were used to measured the temperature at the depth of the body. The heated rigion was in 1 2 cm from the body surface. The measurement results fit to the hyperthermia script.

An experiment on monitoring the dynamics of internal temperature variation in a model object by the acoustic thermography method is carried out. The measurements were performed in a cell filled with an aqueous solution of glycerol, into which a plasticine object was placed. Thermal acoustic radiation of the object was measured in the course of its heating and cooling. Two bars of acoustic thermometers positioned on two sides of the object were used for this purpose. The results of measurements allowed the reconstruction of the dynamics of the varying two-dimensional distribution of in-depth temperature. The position of the heated region, its temperature, and its characteristic size are estimated. In addition, an estimate is obtained for the absorption coefficient.

Theoretical and experimental studies on the localization of heated objects by the methods of acoustic brightness thermometry are carried out. It is demonstrated that, in the case of using a single focusing array, the spatial localization of heated objects depends on the size of the source. One-and two-dimensional tomography of a real heated source is performed by an acoustic thermal tomograph with a focusing array. The results agree well with the data calculated according to the suggested model. The applicability of correlation focusing acoustic brightness thermometry to the localization of a heated source is investigated both theoretically and experimentally. It is demonstrated that a considerable increase in the spatial resolution of the method leads to a significant loss in sensitivity.

Mapping of internal temperature field in biological tissues is one of urgent problems of modern medical diagnostics. One of possible ways of obtaining internal temperature distribution is in application of focused antennae with large aperture and small focal waist in acoustical brightness thermometers (ABT). This work presents the developed ABT with focused antenna as well as the results of experimental investigation of localization of heated sources by spatial scanning of focused antenna for two different regimes of signal receiving - compensation and correlation ones. Besides that the receiving antenna field for these regimes was investigated experimentally. The phantom in the form of polystyrene tube filled with heated oil and placed in water was used as a source in the experiments on object localization. 2D scanning was carried out by displacement of receiving antenna along principal axis. Maximum value of ABT output signal was observed when phantom was positioned in antenna focus. No solving of inverse problem is required to obtain tomographic image, thus improving efficiency and reliability of object localization. This work was supported by Russian Foundation for Basic Research (Projects # 00-02-16600, 01-02-06417, 01-02-17645) and 6th competition-expertise of young scientists of Russian Academy of Sciences (Project #399).

Method of acoustical thermometry based on the registration of acoustical radiation produced by thermal motion of atoms and molecules allows mapping internal temperature field inside biological tissues. Investigations in this area are directed to the improvement of receiving methods and processing algorithms. Present paper is devoted to die investigation of one method of acoustical radiation measurement using acoustical thermograph with focused antenna. An operating laboratory prototype of acoustical thermograph is described. The results of experimentally measured receiving field of focused antenna in focal planeare presented. The possibility of localization of heated sources by means of acoustical thermograph with focused antenna has been demonstrated experimentally. This work was supported by RFBR (Project # 00-02-16600; 01-02-06417; 01-02-17645) and 6th competitive expertise of RAS young scientists (Project #399).