Temperature and SAR measurement errors in the evaluation of metallic linear structures heating during MRI using fluoroptic probes

The purpose of this work is to evaluate the error associated with temperature and SAR measurements using fluoroptic temperature probes on pacemaker (PM) leads during magnetic resonance imaging (MRI). We performed temperature measurements on pacemaker leads, excited with a 25, 64, and 128 MHz current. The PM lead tip heating was measured with a fluoroptic thermometer (Luxtron, Model 3100, USA). Different contact configurations between the pigmented portion of the temperature probe and the PM lead tip were investigated to find the contact position minimizing the temperature and SAR underestimation. A computer model was used to estimate the error made by fluoroptic probes in temperature and SAR measurement. The transversal contact of the pigmented portion of the temperature probe and the PM lead tip minimizes the underestimation for temperature and SAR. This contact position also has the lowest temperature and SAR error. For other contact positions, the maximum temperature error can be as high as -45%, whereas the maximum SAR error can be as high as -54%. MRI heating evaluations with temperature probes should use a contact position minimizing the maximum error, need to be accompanied by a thorough uncertainty budget and the temperature and SAR errors should be specified.     

Temperature measurement on tissue surface during laser irradiation

Tissue surface temperature distribution on the treatment site can serve as an indicator for the effectiveness of a photothermal therapy. In this study, both infrared thermography and theoretical simulation were used to determine the surface temperature distribution during laser irradiation of both gel phantom and animal tumors. Selective photothermal interaction was attempted by using intratumoral indocyanine green enhancement and irradiation via a near-infrared laser. An immunoadjuvant was also used to enhance immunological responses during tumor treatment. Monte Carlo method for tissue absorption of light and finite difference method for heat diffusion in tissue were used to simulate the temperature distribution during the selective laser photothermal interaction. An infrared camera was used to capture the thermal images during the laser treatment and the surface temperature was determined. Our findings show that the theoretical and experimental results are in good agreement and that the surface temperature of irradiated tissue can be controlled with appropriate dye and adjuvant enhancement. These results can be used to control the laser tumor treatment parameters and to optimize the treatment outcome. More importantly, when used with immunotherapy as a precursor of immunological responses, the selective photothermal treatment can be guided by the tissue temperature profiles both in the tumor and on the surface.     

Temperature changes on the root surfaces of mandibular incisors after an 810-nm high-intensity intracanal diode laser irradiation

Temperature changes caused by laser irradiation can promote damage to the surrounding dental tissues. In this study, we evaluated the temperature changes of recently extracted human mandibular incisors during intracanal irradiation with an 810-nm diode laser at different settings. Fifty mandibular incisors were enlarged up to an apical size of ISO No. 40 file. After the final rinse with 17% ethylenediaminetetraacetic acid, 0.2% lauryl sodium sulfate biologic detergent, and sterile water, samples were irradiated with circular movements from apex to crown through five different settings of output power (1.5, 2.0, 2.5, 3.0, and 3.5 W) in continuous mode. The temperature changes were measured on both sides of the apical and middle root thirds using two thermopar devices. A temperature increase of 7 °C was considered acceptable as a safe threshold when applying the diode laser. RESULTS: The results showed that only 3.5-W output power increased the outer surface temperature above the critical value. CONCLUSION: The recommended output power can be stipulated as equal to or less than 3 W to avoid overheating during diode laser irradiation on thin dentin walls.     

Temperature measurement errors with thermocouples inside 27 MHz current source interstitial hyperthermia applicators.

The multielectrode current source (MECS) interstitial hyperthermia (IHT) system uses thermocouple thermometry. To obtain a homogeneous temperature distribution and to limit the number of traumas due to the implanted catheters, most catheters are used for both heating and thermometry. Implications of temperature measurement inside applicators are discussed. In particular, the impact of self-heating of both the applicator and the afterloading catheter were investigated. A one-dimensional cylindrical model was used to compute the difference between the temperature rise inside the applicators (deltaTin) and in the tissue just outside the afterloading catheter (deltaTout) as a function of power absorption in the afterloading catheter, self-heating of the applicator and the effective thermal conductivity of the surrounding tissue. Furthermore, the relative artefact (ERR), i.e. (deltaTin - deltaTout)/deltaTin, was measured in a muscle equivalent agar phantom at different positions in a dual-electrode applicator and for different catheter materials. A method to estimate the tissue temperature by power-off temperature decay measurement inside the applicator was investigated. Using clinical dual-electrode applicators in standard brachytherapy catheters in a muscle-equivalent phantom, deltaTin is typically twice as high as deltaTout. The main reason for this difference is self-heating of the thin feeder wires in the centre of the applicator. The measurement error caused by energy absorption in the afterloading catheter is small, i.e. even for materials with a high dielectric loss factor it is less than 5%. About 5 s after power has been switched off, Tin in the electrodes represents the maximum tissue temperature just before power-off. This delay time (t(delay)) and ERR are independent of Tin. However, they do depend on the thermal properties of the tissue. Therefore, ERR and t(delay) and their stability in perfused tissues have to be investigated to enable a reliable estimation of the tissue temperatures around electrodes in clinical practice.     

Comparison of Ceramide Production with PLC Irradiated by 810 nm LED and 808 nm Laser

Due to its major role in maintaining the water-retaining properties of the epidermis, ceramide is of great commercial potential in cosmetics and pharmaceuticals such as hair and skin care products. However, current synthetic approaches for ceramide are tedious and time-consuming for industrial applications. Therefore, it is desirable to find an alternative cost-efficient and highly-yield method for obtaining the valuable products. In present study, the potential of producing ceramide through enzymatic hydrolysis of sphingomyelin with enzyme irradiated by 808 nm light has been studied. With enzyme irradiated by 808 nm light, its activity can be enhanced and reaction speed can be increased significantly.     

低强度532nm激光的抗氧化损伤效应研究

目的探讨低强度532nm激光的抗氧化损伤效应及其安全照射剂量.材料与方法用532 nm激光对四组(A、B、C、D)健康日本大耳白家兔血管内照射,照射总剂量(光针出口处辐照量)依次为400×104J/cm2、9.86×104J/cm2、1.56×105J/cm2、237×105J/cm0.于照前及照后1 d、4d、7 d、11d检测血浆中SOD活性和MDA水平.结果与照前相比,照后A、B两组SOD活性显著降低,C组略有升高,D组先显著降低,后趋于恢复,最后则显著升高;照后C组MDA水平明显降低,其余各实验组均无显著差异.结论532nm激光在低剂量(不超过1.56×105J/cm2,相应的功率为8mW)时可以提高机体的抗氧化损伤能力,高剂量时则可能诱导产生自由基,造成氧化损伤;该激光在功率不超过8mW的情况下是安全的.     

Noninvasive optoacoustic temperature determination at the fundus of the eye during laser irradiation

In all fundus laser treatments of the eye, the temperature increase is not exactly known. In order to optimize treatments, an online temperature determination is preferable. We investigated a noninvasive optoacoustic method to monitor the fundus temperature during pulsed laser irradiation. When laser pulses are applied to the fundus, thermoelastic pressure waves are emitted, due to thermal expansion of the heated tissue. Using a constant pulse energy, the amplitude of the pressure wave increases linearly with an increase in the base temperature of between 30 and 80 degrees C. This method was evaluated in vitro on porcine retinal pigment epithelium (RPE) cell samples and clinically during selective RPE treatment with repetitive microsecond laser pulses. During the irradiation of porcine RPE with a neodymium-doped yttrium (Nd:YLF) laser (527 nm, 1.7 micros, 500 Hz repetition rate, 160 mJ/cm(2)) an increase in the base temperature of 30+/-4 degrees C after 100 pulses was found. During patient treatments, a temperature increase of 60+/-11 degrees C after 100 pulses with a 500-Hz repetition rate and 7+/-1 degrees C after 30 pulses with 100 Hz at 520 mJ/cm(2) was found. All measured data were in good agreement with heat diffusion calculations. Optoacoustic methods can be used to noninvasively determine retinal temperatures during pulsed laser treatment of the eye. This technique can also be adapted to continuous-wave photocoagulation, photodynamic therapy and transpupillary thermotherapy, or other fields of laser-heated tissue.     

650 nm低能激光对高胆固醇家兔模型血液红细胞的影响研究

目的 研究650 nm低能激光对高胆固醇家兔耳廓根部进行照射对其血液红细胞结构和功能的影响.方法 选择16只雄性家兔,给予家兔高脂饲料,制备高胆固醇症家兔模型,将造模成功家兔随机分为治疗组和模型组,每组6只;另选择6只血脂正常动物作为对照组.治疗组采用650 nm半导体激光进行耳廓根部照射,激光能量100 mW,照射频率：2次/d,30 min/次,6d/周,共治疗16周.正常对照组、模型组不做处理.每4周采集耳缘静脉血液进行血液常规和生化分析,治疗结束后做血液滴片镜下观察红细胞聚集状态.结果 与对照组比较,治疗组红细胞总数降低,模型组红细胞数量偏高,3组差异有统计学意义（P＜0.05）.血红蛋白含量各组间差异无统计学意义（P＞0.05）.治疗组红细胞压积较对照组略低,模型组压积较对照组偏高;模型组红细胞粘连程度较高,而治疗组红细胞粘连聚集程度有所改善,但血液中总胆红素含量偏高.结论 大剂量低能激光血液照射对高血脂家兔的红细胞数量、细胞压积及聚集和黏附状态有影响,且可能对红细胞有一定的破坏作用,引起总胆红素的升高.     

Elimination of breathing artefacts from impedance cardiograms at rest and during exercise

A signal processing technique was developed by which breathing artefacts can be eliminated from impedance cardiograms. The breathing component of the transthoracic impedance signal is identified by a moving-window technique using linear regression analysis, the window span being determined by the current R-R interval of the ECG. Satisfactory beat-by-beat stroke volume measurements were obtained when the method was applied to eliminate simulated breathing artefacts superimposed on distortion-free impedance signals from human subjects. In subjects performing moderate to heavy exercise the potential capability of the method to retrieve the cardiogenic impedance signal in the presence of severe interference caused by exercise hyperpnoea was demonstrated, permitting distortion-free beat-by-beat stroke volume estimations.     

Investigation and improved performance of optical fibre probes in laser Doppler blood flow measurement

Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained.     

635/808 nm双波长半导体激光与632.8 nm氦氖激光照射对术后切口愈合疗效的比较

目的 观察635/808 nm双波长半导体激光与氦氖（He-Ne）激光低强度照射对手术切口愈合疗效的比较.方法 选择非恶性肿瘤手术患者168例,随机分为2组,试验组83例,手术切口予以半导体激光治疗仪低强度照射;阳性对照组85例,手术切口予以He-Ne激光治疗仪照射,以伤口红、肿、热、痛、渗出、裂开等临床表现和不良事件以及切口长度差距为指标观察2组手术切口愈合情况.结果 试验组和对照组切口愈合情况差异无统计学意义（P＞0.05）.结论 双波长半导体激光照射对手术切口愈合的疗效与He-Ne激光治疗效果相当.     

Ultraviolet absorbance at 260 and 280 nm in RNA measurement is dependent on measurement solution

RNA measurement is conducted by measuring ultraviolet absorbance at 260 nm and 280 nm. Calculation of the RNA concentration is based on the absorbance at 260 nm. Furthermore, RNA purity is judged as the 260 nm/280 nm ratio and a low ratio indicates contamination by protein. Diethyl-pyrocarbonate (DEPC)-treated water is used to dissolve RNA and 2-amino-2-hydroxymethyl-1,3-propandiol (Tris) is frequently added to the RNA dissolving solution in order to stabilize the RNA. In the present study, RNA was isolated from mouse liver, and then the influence of DEPC-treated water and Tris-buffer on RNA measurement was studied. The 260 nm/280 ratio of RNA determined after diluting it with distilled water was 1.82+/-0.01 (n=5). DEPC-treated water did not affect the absorbance at 260 nm, but elevated that at 280 nm. Thus, the 260 nm/280 nm ratio was as low as 1.52+/-0.01 (n=5). Tris-HCl (1 M, pH 7.0 or 10.0) lowered the absorbance at 260 nm and even more at 280 nm. Thus, the 260 nm/280 nm ratio was elevated to more than 2.17 (n=5). The present results clearly showed the influence of the measurement solution on RNA measurement.     

650nm低能量激光照射离体高血脂全血和红细胞对其吸收光谱的影响

目的 研究低能量激光照射离体高血脂全血和红细胞对其吸收光谱的影响.方法 选取30例高血脂患者血样为高血脂组,30例正常血样为正常组,用多功能酶标仪分别对血样的全血和红细胞进行扫描,比较两个样本吸收光谱的异同;选用低能量650 nm激光照射待测血样,用多功能酶标仪对全血和红细胞进行扫描并比较照射前后吸收光谱的变化.结果 高血脂血样的全血和红细胞在416、544、578 nm处的吸收峰值均比正常血样高,因此,可通过光谱吸收峰初步判定血液中血脂异常的情况.650 nm激光照射30例高血脂血样后,红细胞在416、544、578 nm处峰值分别降低,照射前后差异具有统计学意义（P＜0.05）;全血照射后其吸收光谱在416、544、578 nm升高,差异具有统计学意义（P＜0.05）.结论 650 nm低能量激光照射可降低高血脂红细胞对光谱的吸收峰,且有助于改善红细胞膜-浆脂质的平衡,从光谱学角度证明了激光治疗高血脂疾病的可行性.     

The rat esophagus: ultrastructure and radiological aspects of tissue response after 1320 nm Nd:YAG laser irradiation.

Morphological tissue response towards laser treatment was investigated in the esophagi of adult Wistar rats by light- and transmission electron microscopy. The specimens were fixed by perfusion immediately, 2 days and 14 days after laser treatment in order to assess different stages of the healing process. The epithelium of the lasercentre was completely destroyed in the immediate group. The connective tissue showed damaged cells, fused collagenous fibres and occluded blood vessels. Smooth muscle cells presented a vacuolated sarcoplasm and pycnotic nuclei. The cross striation of skeletal muscle cells had disappeared and their nuclei were karyolytic. In a distance of 4 mm from the lasercentre all wall tissues had an almost normal appearance. After 2 days the morphological feature of the lasercentre was the same as in the immediate group. In a distance of 2 mm some layers of flat and intact epithelial cells were observed below the necrotic epithelium. The adjacent connective tissue was infiltrated by inflammatory cells. After 14 days the formation of granulation tissue had caused an occlusion of the lumen in the lasercentre. In a distance of 2 mm the lumen was patent and the wall tissues had been partly restored. As the rat esophagus serves as a model for esophagotracheal fistulae in newborn children we assume the 1320 nm Nd:YAG laser to be a possible application in occlusion of these fistulae.     

Effects of irradiation on the interaction of fluorescent probes with lymphocytes.

Low doses of radiation reduce the rate and magnitude of fluorescent probe interaction with spleen cells. The uptake of 8-anilino-naphthalene sulfonic acid (ANS), but not diphenyl-hexatriene (DPH), is reduced in a dose-dependent fashion in cells that receive 25-100 rads. The effects of irradiation are most evident in a "medium" fluorescent subpopulation with no effect observed for a "dim" subpopulation. Splenic lymphocytes enriched for T cells show lower uptake of ANS, compared with a B-cell-enriched population. In addition, the normal decrease in ANS fluorescence polarization that occurs during the initial 10 minutes of probe interaction is attenuated in irradiated cells. These findings are consistent with the notion that low doses of radiation limit the penetration of ANS, but not DPH, into a less restrictive microenvironment within the plasma membranes of T, but not B, cells.     

Optical density changes of Gafchromic MD-55 film resulting from laser light exposure at wavelengths of 671 nm and 633 nm

Laser-based scanners provide a sensitive means for measuring optical density (OD) of Gafchromic films. Such instruments were reviewed in a recent AAPM report (task group 55) which provided recommendations and information on OD measurements (effect of wavelength, temperature, etc.). The present article reports that variable rate scanners and spot densitometers using laser diodes (671 nm) and HeNe lasers (633 nm) can cause polymerization of Gafchromic film. The light induced polymerization depends on light power, wavelength, beam spot size, dwell time, and prior radiation dose of the film. Measurements were made with a custom built scanner that provided accurate control of light power, light polarization, dwell time, and film position in relation to the beam focus. The results demonstrate that lasers operating with powers of 0.1, 0.5, 1.0, and 1.5 mW produce a nonlinear increase in OD of Gafchromic film. The measured change in OD after 1 min of exposure ranges from 0.150 to 0.244 for a laser diode operating at 0.5 and 1.5 mW, respectively. Tables are included that tabulate the increase in OD for laser power, dwell time, and prior dose. Laser light induced polymerization can have a significant impact on dosimetry measurements acquired using these laser-based systems.     

Morphofunctional characteristics of rat ovarian capillaries during irradiation with low-intensity laser

Continous irradiation with He-Ne laser light changes the structure of ovarian capillary bed in rats. These changes depend on the duration of exposure and class of follicles. Three stages in capillary response have been distinguished: 0.5-5 min (rapid increase in alkaline phosphatase activity in the capillary wall and increase in the specific compactness and diameter of capillaries); 5–30 min (relative stabilization of metric values); after 30 min (stable decrease in the activity of the enzyme and specific compactness of capillaries and increase in their diameter). Perifollicular capillary plexuses of 67–80-μm follicles show the highest sensitivity to laser light. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 126, No. 7, pp. 110–112, July, 1998     

In vivo measurement of the optical interaction coefficients of human tumours at 630 nm

The light distribution within a treatment volume is determined by the source geometry (e.g. superficial or interstitial illumination) and the optical interaction coefficients of the irradiated tissue. We have measured the energy fluence rate at various points within tumours undergoing irradiation with 630 nm light for photodynamic therapy for several source geometries. The relative positions of source and detector fibres were determined using CT scanning techniques. The results of the measurements were then applied to solutions of the diffusion theory which allowed the determination of the absorption coefficient (sigma a = 30.5 +/- 16 m-1), the reduced scattering coefficient (sigma' s = 941 +/- 735 m-1), the effective attenuation coefficient (sigma eff = 261 +/- 49 m-1) and the build-up coefficient which relates surface irradiance to the energy fluence rate at depth (k = 1.6 +/- 0.6). Knowledge of these coefficients allows the transmission of light through tissue to be predicted and hence the optical dosimetry of subsequent treatments to be planned more effectively.     

Application of 1 nm gold probes on paraffin wax sections for in situ hybridisation histochemistry.

An in situ hybridisation technique that uses 1 nm immunogold reagents and silver enhancement was devised to detect biotinylated DNA viral probes in formalin fixed, paraffin wax sections of human cervix. DNA probes labelled with biotin-11-deoxyuridine triphosphate were detected after hybridisation to nucleic acid sequences by an antibiotin antibody, followed by a gold labelled secondary antibody. Silver enhancement then permitted visualisation of the signal at the light microscopic level. The method was reliable and produced less background staining than previously described methods. The signal could be enhanced by epi polarisation microscopy. Furthermore, biotinylated DNA probes may be detected directly by a 1 nm gold labelled goat antibiotin antibody without loss of labelling intensity, and this may be preferable to the longer two layer technique, previously described.