Showing papers in "Medical & Biological Engineering & Computing in 1986"
TL;DR: Transmembrane potentials are found in cardiac tissue by means of an idealised one-dimensional model of cardiac tissue that incorporates intracellular and extracellular current flow paths and allows variable (intracellular) junction resistance.
Abstract: What transmembrane potentials are produced in cardiac tissue in response to the application of defibrillating (or stimulating) currents? Such transmembrane potentials are found here by means of an idealised one-dimensional model of cardiac tissue that incorporates intracellular and extracellular current flow paths and allows variable (intracellular) junction resistance. Markedly different transmembrane potentials were computed near the ends (compared with the centre) of 30- and 60-cell strands. With high junction resistance, periodic positive and negative transmembrane potentials occurred within each cell near the centre of the strand. The results in the aggregate paint a picture quite different from that of uniform depolarisation.
126 citations
TL;DR: Limits exist with the use or the notion of a normal profile of EMG for gait, as a given muscle from a given subject can present specific profiles, but usually these specificities are averaged out in the pooled between-subject data.
Abstract: The aim of the present study was to validate the notion that there is a normal profile for electromyographic (EMG) signals in gait. For eight subjects, surface electrodes were used to record signals over ten strides from the soleus, rectus femoris, biceps femoris, vastus medialis and tibialis anterior muscles. Analyses of EMG linear envelopes, normalised with respect to both time and amplitude, demonstrated that statistically significant differences exist in amplitude of activity across subjects for all muscles, and that within subjects the data were highly repeatable. More importantly, differences in profiles of activity were found especially for the rectus femoris muscle. It was also found that a given muscle from a given subject can present specific profiles, but usually these specificities are averaged out in the pooled between-subject data. Thus limits exist with the use or the notion of a normal profile of EMG for gait.
118 citations
TL;DR: Two additional solution procedures are provided, one exact and one approximate, the latter relatively simple, and the results show that the exact method provides almost identical transmembrane values; the approximate method gives values within 2 per cent.
Abstract: If a defibrillating stimulus current is applied to a one-dimensional fibre, and if the fibre has junction resistances joining the individual cells, what pattern of transmembrane voltages is induced by the stimulus, and what are the curretns that flow to produce the transmembrane voltages? These questions were considered in an earlier report; in this paper, two additional solution procedures are provided, one exact and one approximate, the latter relatively simple. Earlier work used a resistive model of the cells and junctions, together with a computer solution of 330 simultaneous equations for a 30-cell fibre. The present methods exploit the known solutions for the continuous (zero junctional resistance) fibre together with an analytic treatment of the junctions. With the present methods solution for currents and transmembrane potentials in the same 30-cell fibre requires a solution of only 29 equations (exact method) or the solution of none at all (the approximate method). The results show that, compared with previous results, the exact method provides almost identical transmembrane values; the approximate method gives values within 2 per cent.
95 citations
TL;DR: It was found that the contact ratio is the predominant factor producing the change of skin admittance induced by changes in the water content of skin.
Abstract: The properties of skin adminttance were investigated with the intention of applying them to skin moisturisation measurement. Skin admittance is determined by measuring relative permittivity and the resistivity of the stratum corneum, and by contact ratio between dry electrode and stratum corneum. It was found, however, that the contact ratio is the predominant factor producing the change of skin admittance induced by changes in the water content of skin. To measure skin admittance, the following conditions were found to be approriate: (a) frequency of about 100 kHz; (b) concentric electrodes, the diameter of the measuring (inner) electrode being about 5 mm, and (c) an electrode pressure of about 100 g cm−2. Based on these optimal conditions, a system for measuring skin admittance was constructed. All measuring procedures were automated. Experimental observations made with this system have indicated its usefulness for the measurement of skin moisturisation.
79 citations
TL;DR: It is concluded that, in respect of safe deliverable charge density per pulse at the electrode, release of noxious products and stimulating effectiveness, simple pulses need give no worse performance; in some circumstances they may give better.
Abstract: Actively balanced (‘Lilly’) stimulating current waveforms are generally considered to give very ‘safe’ stimulation. Although this is perfectly true, the specification of the necessary waveform generators in neurological prostheses demands additional complexity, and probably additional expense and development time as well. The paper and its companion enquire whether the use of simple, passively charge-balanced stimulating pulses is equally safe, provided the stimulation parameters and circuitry are designed with appropriate care. It is concluded that, in respect of safe deliverable charge density per pulse at the electrode, release of noxious products and stimulating effectiveness, simple pulses need give no worse performance; in some circumstances they may give better.
77 citations
TL;DR: A probe for measurement of related values of cross-sectional area (CA) and pressure in a biological tube has been developed to study passive and active closure forces in the female urethra and evaluation of the urethral closure function in terms of isometric contraction, isotonic contraction, muscular work and power can be performed.
Abstract: A probe for measurement of related values of cross-sectional area (CA) and pressure in a biological tube has been developed to study passive and active closure forces in the female urethra. CA is measured in the range 0·13–1·00 cm2 by the field gradient technique. The system is able to produce an arbitrarily chosen CA in the urethra in about 50 ms. Pressure is measured in the range 0–150 cm H2O (0–14·7 kPa) by a microtransducer. The risetime of the pressure measuring system is 2·5 ms. Pressure needed for inflation and deflation of the balloon ranges from 2 to −5 cm H2O (0·2 to −0·5 kPa). The hysteresis of the balloon is approximately 1 cm H2O (0·1 kPa). The method permits estimation of urethral distensibility (rigidity/compliance), the real (noninstrumented) urethral closure pressure and urethral hysteresis. Furthermore, evaluation of the urethral closure function in terms of isometric contraction, isotonic contraction, muscular work and power can be performed.
74 citations
TL;DR: It is shown experimentally on the biceps, extensor digitorum and first dorsal interosseus muscles that an excellent agreement exists between the time averages of Fm and ZCR in normal muscles under a variety of muscle length tension and fatigue conditions.
Abstract: A system is described which monitors spectral changes of the surface EMG. It is shown analytically that a relationship exists between the zero crossing rate (ZCR) and the mean, Fa, and median, Fm, frequencies of the surface EMG. Under the existing conditions of this relationship a system can be built which can estimate and monitor the Fa or Fm of the surface EMG from the measured ZCR. It is shown experimentally on the biceps, extensor digitorum and first dorsal interosseus muscles that an excellent agreement exists between the time averages of Fm and ZCR in normal muscles under a variety of muscle length tension and fatigue conditions. A simple portable microcomputer unit which performs the ZCR calculations and which can be used as a muscle fatigue monitor is described.
72 citations
TL;DR: It is found that the pressure/volume relationship of common carotid arteries is well represented by an exponential of the form V/Vo=Keαf(P), which was derived as the inverse solution to the Moens-Korteweg equation.
Abstract: Pulse wave velocity (PWV) was measuredin situ in 11 isolated canine common carotid arteries. Seven arteries exhibited a linear PWV/pressure function at pressures ranging from 0 to 200 mm Hg. Four arteries yielded a linear relationship between PWV and pressure between 1 and 100 mm Hg; for these vessels the relationship was nonlinear at higher pressures. Seven arteries (five from the group which was linear up to 200 mm Hg and two from the group which was linear up to 100 mm Hg) were excised and presure/volume measurements were madein vivo. Using pressure/volume data, the Moens-Korteweg equation was evaluated as a predictor of the PWV/pressure relationship over the linear region. An expression was developed to anable prediction of the pressure/volume relationship using the coefficients at the linear PWV/pressure function; these predictions were evaluated. We found that, for this range, the Moens-Korteweg equation provides a very good basis for predicting the increase in PWV with increasing bias pressure. In addition, we found that the pressure/volume relationship of common carotid arteries is well represented by an exponential of the form V/Vo=Keαf(P), which was derived as the inverse solution to the Moens-Korteweg equation.
71 citations
TL;DR: A new integrating probe for laser Doppler flowmeters was developed, which receives light from seven different scattering volumes simultaneously, and processes an integrated signal which is ultimately taken as the average flow value.
Abstract: Methods to measure microvascular blood flow usually probe small volumes of tissue. Therefore, spatial differences in skin blood flow alter the signal, when the sensing element is moved a short distance. To reduce the effects of spatial differences in skin blood flow, but yet record its temporal variability, a new integrating probe for laser Doppler flowmeters was developed. The probe receives light from seven different scattering volumes simultaneously, and the instrument processes an integrated signal which is ultimately taken as the average flow value. Significant spatial integration is found, as spatial variability is reduced by the square root of the number of scattering volumes.
66 citations
TL;DR: The model results show an apparent frequency dependence of the electrical conductivity of skeletal muscle tissue, as well as the way the conductivity is affected by the length the current is conducted.
Abstract: Recent experiments carried out in our laboratory with the four-electrode method showed that the electrical conductivity of skeletal muscle tissue depends on the frequency of the injected current and the distance between the current electrodes. A model is proposed in order to study these effects. The model takes into account the structure of the tissue on the scale of individual fibres. It discerns three main components with respect to electrical properties: (a) extracellular medium with electrical conductivity σe; (b) intracellular medium with electrical conductivity σi; (c) muscle fibre membrane with impedance Zm. The model results show an apparent frequency dependence of the electrical conductivity of skeletal muscle tissue, as well as the way the conductivity is affected by the length the current is conducted.
60 citations
TL;DR: An improved continuous reading fluorophotometer with provision for controlling the blink rate has been used to measure tear turnover rates in 14 normal healthy volunteers, and a significant difference between morning and afternoon tear turnover results has been found, indicating a possible circadian rhythm in tear flow.
Abstract: An improved continuous reading fluorophotometer with provision for controlling the blink rate has been used to measure tear turnover rates in 14 normal healthy volunteers. A significant difference between morning and afternoon tear turnover results has been found, indicating a possible circadian rhythm in tear flow. Sources of potential systematic error in the measurement method have been identified and analysed. Fluorescence measurements using a thin film cell have confirmed predictions of nonlinearity in fluorophotometer output at high tear film concentrations. The error in tear film fluorescence due to diffusion of fluorescein into the cornea has also been investigated. Simple precautions to minimise these errors are suggested, which should make the measurement method suitable for clinical application.
TL;DR: Measurements of frequency-dependent attenuation in normal and pathological breast tissue indicate that the attenuation coefficient is lower for tissues with large predominance of cells and increases with collagen fibre content.
Abstract: The present paper reports on measurements of frequency-dependent attenuation in normal and pathological breast tissue. Measurements were performed by using pulsed transmitted ultrasound. Five groups of breast specimens including fatty tissue, fibrofatty parenchyma and fibrosis, malignant tumours with and without productive fibrosis (infiltrating ductal carcinoma scirrhous type and medullary carcinoma, respectively) have been studied. The results of the attenuation measurements indicate that the attenuation coefficient is lower for tissues with large predominance of cells (fatty tissue, medullary carcinoma) and increases with collagen fibre content (infiltrating ductal carcinoma scrirrhous type, fibrosis, fibrofatty). A comparative nonlinear (best fitting) and linear analysis of the attenuation curves shows that it does not matter whether one uses a linear or nonlinear equation to describe the attenuation curves.
TL;DR: The selection of perturbation parameters is discussed in the light of general requirements for persistent excitation, accurate identification, stationarity and subject safety.
Abstract: Postural perturbations are often used in experimental investigations of human balance and postural control. Treating the perturbation as the input and the resulting postural sway response as the output, an input/output model of the posture-control system can be identified. Selection of the perturbation parameters can have a substantial influence on the accuracy of the identification and on the interpretation of the results. Pertinent parameters include type of perturbation, waveform, power spectrum, bandwidth, amplitude and test duration. The selection of these parameters is discussed in the light of general requirements for persistent excitation, accurate identification, stationarity and subject safety. Experimental results are used to illustrate specific issues.
TL;DR: Flow rate and total volume flow under compression were calculated and found to vary with the degree of oedema, which provides important information for diagnosis and treatment.
Abstract: A well defined step compression was applied over an area of the skin and maintained for a fixed time. The resistive force of the tissue, which was continuously recorded, decreased with time as a function of the translocation of fluid volume to the surrounding areas. The rate of decrease was proportional to the fluid mobility. Measurements on ten normal subjects and 14 oedematous patients showed marked differences in the pattern of fluid translocation. Flow rate and total volume flow under compression were calculated and found to vary with the degree of oedema. This noninvasive technique can measure the degree of oedema, which provides important information for diagnosis and treatment.
TL;DR: It is concluded that a computer may advantageously be used to accept daily blood glucose estimates and recommend changes in insulin therapy, that these dosage changes should improve glycaemic control, and that the development of a portable insulin dosage microcomputer device can provide both the patient having diabetes mellitus and his physician with a new and unique method for significantly improving conventional insulin therapy.
Abstract: The paper presents a three-way comparative study of the responses of computer-simulated diabetic patients to intervention for insulin dosage adjustment either by a diabetologist according to conventional methods or by the patient himself according to either recommended manual methods or a newly developed computerimplementable algorithm. In all cases, insulin dosage adjustment improved glycaemic control. However, the new computer algorithm described in this report was superior both in respect to the speed of improving diabetes control and the avoidance of undesirable hypoglycaemia. We conclude, on the basis of our simulations, that a computer may advantageously be used to accept daily blood glucose estimates and recommend changes in insulin therapy, that these dosage changes should improve glycaemic control (as assessed by reductions in both the mean premeal glycaemia and its variability), and finally that the development of a portable insulin dosage microcomputer device can provide both the patient having diabetes mellitus and his physician with a new and unique method for significantly improving conventional insulin therapy.
TL;DR: It is concluded that, in respect of safe deliverable charge density per pulse at the electrode, release of noxious products and stimulating effectiveness, simple pulses need give no worse performance; in some circumstances they may give better.
Abstract: Actively balanced (‘Lilly’) stimulating current waveforms are generally considered to give very ‘safe’ stimulation. Although this is perfectly true, the specification of the necessary waveform generators in neurological prostheses demands additional complexity, and probably additional expense and development time as well. The paper and its companion enquire whether the use of simple, passively charged-balanced stimulating pulses is equally safe, provided the stimulation parameters and circuitry are designed with appropriate care. It is concluded that, in respect of safe deliverable charge density per pulse at the electrode, release of noxious products and stimulating effectiveness, simple pulses need give no worse performance; in some circumstances they may give better.
TL;DR: A new physical model to simulate the gastric electrical activity (ECA and ERA) as picked up at points on the stomach wall and on the abdominal surface is proposed, which reproduces not only the spatial and temporal organisation of the gastrics electrical activity but also its morphological characteristics as obtained by experiments in vivo.
Abstract: A new physical model to simulate the gastric electrical activity (ECA and ERA) as picked up at points on the stomach wall and on the abdominal surface is proposed. In this model the part of the stomach where the electrical activity originates and propagates is represented by a truncated cone of finite length; the electrical potential representing the electrical activity of the cell is generated by a distal movement of an annular band polarised by electric dipoles which are oriented perpendicularly to the surface of the cone. The model reproduces not only the spatial and temporal organisation of the gastric electrical activity (ECA and ERA) but also its morphological characteristics (waveform, amplitude, frequency, phase lag) as obtained by experimentsin vivo. This model also reproduces the morphological characteristics of the signal as picked up, by experimentsin vivo on the abdominal surface in man.
TL;DR: With a model based on Poisson's equation, computations employing published data and measurements made in glass cylinders filled with saline, the influence of conductivity and geometry on the determination of volume was analysed with an impedancimetric catheter and it was concluded that each section ought to be independently calibrated.
Abstract: With a model based on Poisson’s equation, computations employing published data and measurements made in glass cylinders filled with saline, the influence of conductivity and geometry on the determination of volume was analysed with an impedancimetric catheter. Two distal electrodes inject a constant current while a set of central electrodes sense by sections the potential along the cylindrical chamber. It was concluded that each section ought to be independently calibrated, the distribution of the electrodes along the catheter and its relationship to the chamber radius being of paramount importance for a linear calibration. The ratio σr, of the external medium conductivity σe to the internal conductivity σi influences drastically both the linearity and the calibration of each section. If a section volume is linearly related to the total chamber volume, that section admittance is a total volume estimator.
TL;DR: A method of analysing multiple-breath nitrogen washouts is described and discussed, which is objective and introduces no weighting into the results, and suitable for clinical online applications.
Abstract: A method of analysing multiple-breath nitrogen washouts is described and discussed. The method is objective and introduces no weighting into the results. The necessary raw data are obtained from a computer-assisted nitrogen washout test. During the analysis, objective parameters which characterise the alveolar ventilation in terms of nitrogen elimination pattern and gas-mixing efficiency are calculated, together with estimates of functional residual capacity (FRC), tidal volume, dead space, and effective part of the tidal volume. The elimination pattern is described through linear fitting of exponential models to the obtained washout course and is performed by using the z-transform. The dead space and the effective part of the tidal volume are estimated from a gas-mixing model. The applied estimation procedure difines a dead space which is larger than the corresponding single-breath dead space and has been designated ‘effective dead space’. The gas-mixing efficiency is described by two indices, one describing the efficiency within an idealised breath and the other the overall efficiency of the lungs. The calculation algorithms are fast and the results are easy to interpret, which makes the method suitable for clinical online applications. The method has been evaluated in a group of 24 healthy newborns at about 26 hours of age, but the application is not restricted to this category of patient.
TL;DR: Intravaginal electrical stimulation was used in the cat to induce bladder inhibition and urethral closure and the chopped pulse was the least efficient stimulus, since the threshold voltage was comparable to that of the 0·5 ms duration alternating pulse, implying a five times higher power dissipation.
Abstract: Intravaginal electrical stimulation (IVS) was used in the cat to induce bladder inhibition and urethral closure. The purpose of the study was to compare the efficacy of alternating constant-voltage pulses of different durations (0·1, 0·2, 0·5 and 5 ms) with that of chopped alternating pulses, each consisting of a train of five 0·5 ms pulses with 0·5 ms pauses between. The voltage requirement for an equal biological effect was lowest for the 5 ms alternating pulse, whereas the pulse power dissipation was lowest for the 0·1 ms pulse, about 10 per cent of that for the 5 ms pulse. If both voltage requirement and power dissipation are taken into account, the 0·5 ms pulse was considered the most appropriate compromise. The chopped pulse was the least efficient stimulus, since the threshold voltage was comparable to that of the 0·5 ms duration alternating pulse, implying a five times higher power dissipation. For bladder inhibition, the optimal stimulation frequency for alternating pulses was 10 Hz, both in terms of threshold voltage and power consumption. For urethral closure the voltage requirement was lowest at 50 Hz but 20 Hz was preferable in terms of power dissipation for an equal, although submaximal, effect.
TL;DR: Evidence shows that in these neutral solutions corrosion occurs when the positive voltage excursion is great enough for acid to be evolved locally by the oxidation of water.
Abstract: The corrosion of platinum electrodes in saline is studied by measuring loss of metal resulting from the passage of current and plotting the data on the electrode fimit-voltage plane (ELVP). Some results show that with this form of presentation, the effects of current density, pauses in the current and the presence of blood serum (to imitate extracellular fluid), is not strong. Evidence shows that in these neutral solutions corrosion occurs when the positive voltage excursion is great enough for acid to be evolved locally by the oxidation of water. When electrode voltage is not controlled and it is capacitor-coupled (e.g. in practical stimulators). serum has a beneficial effect on the voltage, tending to reduce corrosion.
TL;DR: Tâche poursuite aleatoire, tâche Poursuite a pas et tâches poursuites mixte sont les 3 systemes informatiques etudies.
Abstract: Tâche poursuite aleatoire, tâche poursuite a pas et tâche poursuite mixte sont les 3 systemes informatiques etudies
TL;DR: The results may be summarised as follows: the power of photoplethysmograms of a finger and a toe is concentrated in the range below 6 or 8 Hz; age correlates highly with the transmission time of a pulse wave rather than with velocity.
Abstract: Pulse wave patterns at a finger and a toe are obtained using photoplethysmography. The data recorded at two recording sites are transformed by digital filters into six waveforms and the transmission time of each wave is estimated by the crosscorrelation function. Relationships between the transmission times, age, and parameters obtained from several laboratory tests are examined using multiple regression analysis. The results may be summarised as follows: the power of photoplethysmograms of a finger and a toe is concentrated in the range below 6 or 8 Hz; age correlates highly with the transmission time of a pulse wave rather than with velocity; the multiple correlation coefficients between age and the transmission times is 0·853 in male and 0·866 in female; there are no differences of transmission time among disease types; the correlations between age and other parameters measured by laboratory tests, that is, total cholesterol, phospholipid, triglyceride, β-lipoprotein, are very small.
TL;DR: The simulated shape of the LV during the entire cardiac cycle reasonably compares with the experimental data and the twist angle of the ventricle as well as its maximal mean fibre strain are found to be in good agreement with physiological findings.
Abstract: The model of the left ventricle (LV) mechanics presented in Part 1 of the paper is used to simulate an entire cardiac cycle Time-sequential canine heart data obtained by dynamic computerised tomography serve to initiate the simulation as well as to provide real data for evaluation of its results The numerical predictions of the dynamic geometric changes are in good agreement with the tomographically determined changes that the ventricle undergoes throughout the cycle Moreover, the simulation allows the evaluation of the time-varying stress and strain distributions in the ventricular wall and the active forces prevailing in the myocardial fibres The simulated shape of the LV during the entire cardiac cycle reasonably compares with the experimental data Furthermore, the twist angle of the ventricle as well as its maximal mean fibre strain are found to be in good agreement with physiological findings Finally, a parametric study gives the relative influence of the anisotropy of the myocardium, its geometric and material nonlinearities and the mechanical activation on the mechanics of the left ventricle
TL;DR: The possible influence of time-varying magnetic fields on action potential in the lobster giant axon was studied, and a method is proposed for estimating the threshold values of magnetic flux density for nerve excitation.
Abstract: The possible influence of time-varying magnetic fields on action potential in the lobster giant axon was studied. The axon membrane was excited by galvanic stimulation and the action potential was recorded intracellularly with microelectrodes. During the propagation of the action potential along the axon, alternating or pulsed magnetic fields were applied across the middle part of the axon to study whether or not magnetic fields have any effect on parameters such as conduction velocity and refractory period of the nerve fibre and amplitude, duration and shape of the action potentials. No effect on these parameters was observed under different flux densities and frequencies of the magnetic fields. When simulating the conductive properties of tissue surrounding the nerve with the aid of an external conducting loop with a load resistance, action potentials were generated which made it possible to study the threshold value of the induced eddy current for nerve excitation. Based on the results of the experiment, the influence of magnetic flux density, frequency, conductivity, induced EMF and induced eddy current density is discussed, and a method is proposed for estimating the threshold values of magnetic flux density for nerve excitation.
TL;DR: The electrode limitvoltage plane (ELVP) as discussed by the authors is a tool for describing in electrical terms what a polarisable electrode is doing under a particular set of conditions, such as charge-injection.
Abstract: The paper introduces the electrode limit-voltage plane (ELVP)—a useful tool for describing in electrical terms what a polarisable electrode is doing under a particular set of conditions. The ELVP is then used to consider the charge-injection capability of a platinum stimulating electrode.
TL;DR: Using this instrument, the progressive and regressive changes in arterial elastic properties have been clearly demonstrated in the forelegs of hyperlipoedemic rabbits with experimental atherosclerosis.
Abstract: A new instrument for the noninvasive measurement of arterial elastic properties such as ‘pressure-volume relationship’ and ‘volume elastic modulus’ in human fingers or in rabbit forelegs has been designed using a transmittance infra-red photoelectric plethysmography technique. The measurement and display of the results by this system is carried out automatically by use of a conventional personal computer. Using this instrument, the progressive and regressive changes in arterial elastic properties have been clearly demonstrated in the forelegs of hyperlipoedemic rabbits with experimental atherosclerosis. The effect of vasodilation by isosorbide dinitrate on the finger arteries of patients with congestive heart failure was also successfully studied. This instrument is capable of a rapid and reliable measurement of arterial elasticity and appears to be useful not only in basic cardiovascular research laboratories but also in clinics.
TL;DR: It is demonstrated that the time selection process may provide a substantial improvement to the laser tomoscopy technique when used for imaging biological media.
Abstract: A Monte Carlo model has been developed to study the propagation of an ultrashort light pulse through a heterogeneous thick biological specimen. A circular blood vessel is moved within a tissular slab to simulate biological specimen scanning using a picosecond laser source and a collimated ultrafast multichannel opticl shutter. Features of the transmitted light are computed for each position of the blood vessel. The computer program gives an account of the transmitted photons, the flight time which does not exceed straightforward crossing time plus time gate of known duration. A small blood vessel (radius R=2 mm) placed in a 40 mm thick slab is easily located when a time gate of 10 ps duration is employed. Such a time gate also allows the detection of a middle-sized vessel (R=4 mm) embedded in a thicker sample (80 mm). The contrast computed for the transmittance profile is greatly improved when a time gate is used. In addition, shifting of the blood vessel towards the unilluminated side of the sample decreases the contrast. We demonstrate that the time selection process may provide a substantial improvement to the laser tomoscopy technique when used for imaging biological media.