T. Jayakumar

Medical applications of infrared thermography: A review

Abstract Abnormal body temperature is a natural indicator of illness. Infrared thermography (IRT) is a fast, passive, non-contact and non-invasive alternative to conventional clinical thermometers for monitoring body temperature. Besides, IRT can also map body surface temperature remotely. Last five decades witnessed a steady increase in the utility of thermal imaging cameras to obtain correlations between the thermal physiology and skin temperature. IRT has been successfully used in diagnosis of breast cancer, diabetes neuropathy and peripheral vascular disorders. It has also been used to detect problems associated with gynecology, kidney transplantation, dermatology, heart, neonatal physiology, fever screening and brain imaging. With the advent of modern infrared cameras, data acquisition and processing techniques, it is now possible to have real time high resolution thermographic images, which is likely to surge further research in this field. The present efforts are focused on automatic analysis of temperature distribution of regions of interest and their statistical analysis for detection of abnormalities. This critical review focuses on advances in the area of medical IRT. The basics of IRT, essential theoretical background, the procedures adopted for various measurements and applications of IRT in various medical fields are discussed in this review. Besides background information is provided for beginners for better understanding of the subject.

Ultrasonic velocity measurements for estimation of grain size in austenitic stainless steel

Ultrasonic velocity measurements have been used to estimate average grain size in an AISI type 316 stainless steel. For precise ultrasonic transit time measurements, the pulse-echo-overlap technique has been used. Master graphs relating ultrasonic velocity with metallographically obtained grain size have been generated. Using these graphs, grain sizes in new specimen have been obtained. The results indicate that grain size can be predicted with good confidence level using ultrasonic velocity measurements. Shear waves are found to be more sensitive for grain size measurement, as compared to longitudinal waves. The grain size estimated by velocity measurements is found to be more accurate when compared to that obtained by attenuation measurements.

Temperature distribution and residual stresses due to multipass welding in type 304 stainless steel and low carbon steel weld pads

Welding is a reliable and efficient metal-joining process widely used in industry. Due to the intense concentration of heat in the heat source of welding, the regions near the weld line undergo severe thermal cycles, thereby generating inhomogeneous plastic deformation and residual stresses in the weldment. Plates of different thickness are used in industry and these plates are normally joined by multipass welding. In a multipass welding operation, the residual stress pattern developed in the material changes with each weld pass. In the present experimental work, thermal cycles and transverse residual stresses due to each pass of welding have been measured in the weld pads of AISI type 304 stainless steel and low carbon steel with 6, 8 and 12 mm thickness. X-ray diffraction method was used for residual stress measurements. The welding process used was the Manual Metal Arc Welding (MMAW) process. In this paper, the peak temperatures attained at different points during deposition of weld beads in stainless steel and low carbon steel weld pads are compared. The residual stress patterns developed, the change in the peak tensile stress with the deposition of weld beads, and the relation between the peak temperatures and the residual stresses in the weld pads are discussed.

Correlation between Plantar Foot Temperature and Diabetic Neuropathy: A Case Study by Using an Infrared Thermal Imaging Technique

Background: Diabetic neuropathy consists of multiple clinical manifestations of which loss of sensation is most prominent. High temperatures under the foot coupled with reduced or complete loss of sensation can predispose the patient to foot ulceration. The aim of this study was to look at the correlation between plantar foot temperature and diabetic neuropathy using a noninvasive infrared thermal imaging technique. Methods: Infrared thermal imaging, a remote and noncontact experimental tool, was used to study the plantar foot temperatures of 112 subjects with type 2 diabetes selected from a tertiary diabetes centre in South India. Results: Patients with diabetic neuropathy (defined as vibration perception threshold (VPT) values on biothesiometry greater than 20 V) had a higher foot temperature (32–35 °C) compared to patients without neuropathy (27–30 °C). Diabetic subjects with neuropathy also had higher mean foot temperature (MFT) (p = .001) compared to non-neuropathic subjects. MFT also showed a positive correlation with right great toe (r = 0.301, p = .001) and left great toe VPT values (r = 0.292, p = .002). However, there was no correlation between glycated hemoglobin and MFT. Conclusion: Infrared thermal imaging may be used as an additional tool for evaluation of high risk diabetic feet.

Infrared thermal imaging for detection of peripheral vascular disorders

Body temperature is a very useful parameter for diagnosing diseases. There is a definite correlation between body temperature and diseases. We have used Infrared Thermography to study noninvasive diagnosis of peripheral vascular diseases. Temperature gradients are observed in the affected regions of patients with vascular disorders, which indicate abnormal blood flow in the affected region. Thermal imaging results are well correlated with the clinical findings. Certain areas on the affected limbs show increased temperature profiles, probably due to inflammation and underlying venous flow changes. In general the temperature contrast in the affected regions is about 0.7 to 1° C above the normal regions, due to sluggish blood circulation. The results suggest that the thermal imaging technique is an effective technique for detecting small temperature changes in the human body due to vascular disorders.

Assessment of microstructures and mechanical behaviour of metallic materials through non-destructive characterisation

Abstract Non-destructive evaluation (NDE) of materials for characterising various key microstructural features, mechanical properties (tension, creep, fatigue crack growth, hardness and fracture toughness), deformation and damage mechanisms has attracted considerable attention in the past 20 years as a primary step towards ensuring structural integrity of components. However, until recently, the correlations between the various NDE parameters and material properties have been only empirical and based on physical principles. The interaction between the NDE probing medium and the mechanical behaviour is not yet fully understood. The purpose of this review is to discuss the progress made in the application of non-destructive testing (NDT) techniques in evaluating various microstructural features and mechanical properties with emphasis on recent studies. Reinterpretation of older data, in the light of present understanding of the interaction of the NDE probing medium with material parameters, is carried out selectively. The NDT techniques evaluated include acoustic emission, ultrasonic attenuation and velocity, magnetic hysteresis parameters, magnetic Barkhausen emission, acoustic Barkhausen emission, laser interferometry, positron annihilation, X-ray diffraction and small angle neutron scattering. Critical assessments of the applicability of the various NDE techniques for the material parameters are provided.

Magnetic nanoparticles with enhanced γ-Fe2O3 to α-Fe2O3 phase transition temperature

We report a simple method for producing magnetic nanoparticles with enhanced maghemite (?-Fe2O3) to haematite (?-Fe2O3) phase transition temperature. By controlling the properties of the solvent media, we have been able to tune the particle size from 2.3 to 6.5?nm. Nanoparticles with higher transition temperatures have been achieved by using NaOH as an alkali during the co-precipitation. The maghemite to haematite phase transition was complete at a temperature below 600??C for nanoparticles prepared using ammonia, whereas the phase transition was not complete until 750??C for the samples prepared with NaOH. The increase in average particle size after heat treatment at 600??C is attributed to coalescence of particles by solid state diffusion, where the system reduces its free energy by reducing the surface area. The final particle diameters of the haematite after the heat treatment were 35.4, 31.38 and 26.85?nm respectively for nanoparticles of initial diameters 5, 7 and 9.8?nm. Our studies on the effect of the initial particle size on the transition temperature show that the transition temperature decreases with decreasing particle size due to the reduced activation energy of the system.

Microstructural characterization of quenched and tempered 0.2% carbon steel using magnetic Barkhausen noise analysis

Abstract Magnetic Barkhausen noise (MBN) has been used to characterize the microstructures in quenched and tempered 0.2% carbon steel. It has been observed that tempering at 873 K shows a single peak MBN behaviour after 0.5 h and a slope change indicating the development of two peak behaviour after 1 h. After 5 h of tempering, MBN shows a clear two peak behaviour. A two stage process of irreversible domain wall movement during magnetization is proposed considering the grain boundaries and second phase precipitates as the two major obstacles to domain wall movement. The domain walls overcome these two major obstacles over a range of critical field strengths with some mean values characteristic of the obstacles. If these two mean values are close to each other, then a single peak, sometimes associated with a slope change in MBN behaviour, appears. On the other hand, if the mean values of the critical fields of these two barriers are widely separated, then a two peak behaviour appears. The effect of microstructural changes on MBN is explained based on these two stage processes. The influence of dissolution of martensite and the precipitation of cementite (Fe3C) on MBN are explained.

Effect of thermal annealing under vacuum on the crystal structure, size, and magnetic properties of ZnFe2O4 nanoparticles

In this paper, we report the variations in the crystal structure, average particle size, and magnetic properties of ZnFe2O4 nanoparticles on thermal annealing, using in situ high temperature x-ray diffraction (XRD). Fine powder of ZnFe2O4 nanoparticles with an average particle size of 9.3nm, prepared through coprecipitation technique, has been used in these studies. The powder is heated from room temperature to 1000°C, under vacuum in steps of 100°C and the XRD pattern is recorded in situ. A sudden drop in the lattice parameter from 8.478to8.468A is observed at 800°C, above which it increases with increasing temperature. After annealing at 1000°C, the lattice parameter reduces from 8.441to8.399A and the magnetization value increases from 5to62emu∕g, suggesting the possibility of a conversion of the cubic structured ZnFe2O4 from normal to inverse spinel structure due to canting of ions between the tetrahedral and octahedral interstitial sites. During annealing, the Zn2+ ions move from tetrahedral site to o...

On the influence of tempered microstructures on magnetic Barkhausen emission in ferritic steels

Abstract Magnetic Barkhausen emission (MBE) has been used to characterize various microstructures in tempered 0.2 wt% C steel, 2.25Cr—1Mo steel and 9Cr—1Mo steel samples (where the composition is in approximate weight per cent). A two-stage process of irreversible magnetic domain wall movement during magnetization is proposed considering the lath or grain boundaries and second-phase precipitates as the two major obstacles to domain-wall movement. The domain walls overcome these two major obstacles over a range of critical field strengths with some mean values, characteristic of the obstacles. If these two mean values are close to each other, then a single peak, sometimes associated with slope changes, appears in the MBE behaviour. On the other hand, if the mean values are widely separated, then two-peak MBE behaviour appears to indicate the influence of these two major obstacles separately. Based on this, the influence of the dissolution of martensite and/or bainite and the precipitation and growth of the...