On the use of photoacoustics to detect red blood cell aggregation

Study of erythrocyte sedimentation in human blood through the photoacoustic signals analysis

Introduction

In this study, we utilized the pulsed photoacoustic (PA) technique to analyze globular sedimentation in whole human blood, with a focus on distinguishing between healthy individuals and those with hemolytic anemia.

Methods

Blood samples were collected from both healthy individuals (women and men) and those with hemolytic anemia, and temporal and spectral parameters of PA signals were employed for analysis.

Results

Significant differences (p < 0.05) were observed in PA metrics between the two groups. The proposed spectral analysis allowed significant differentiation within a 25-minute measurement window. Anemic blood samples exhibited higher erythrocyte sedimentation rate (ESR) values, indicating increased erythrocyte aggregation.

Discussion

This study underscores the potential of PA signal analysis in ESR assessment as an efficient method for distinguishing between healthy and anemic blood, surpassing traditional approaches. It represents a promising contribution to the development of precise and sensitive techniques for analyzing human blood samples in clinical settings.

Dynamic modeling of photoacoustic sensor data to classify human blood samples

The photoacoustic effect is an attractive tool for diagnosis in several biomedical applications. Analyzing photoacoustic signals, however, is challenging to provide qualitative results in an automated way. In this work, we introduce a dynamic modeling scheme of photoacoustic sensor data to classify blood samples according to their physiological status. Thirty-five whole human blood samples were studied with a state-space model estimated by a subspace method. Furthermore, the samples are classified using the model parameters and the linear discriminant analysis algorithm. The classification performance is compared with time- and frequency-domain features and an autoregressive-moving-average model. As a result, the proposed analysis can predict five blood classes: healthy women and men, microcytic and macrocytic anemia, and leukemia. Our findings indicate that the proposed method outperforms conventional signal processing techniques to analyze photoacoustic data for medical diagnosis. Hence, the method is a promising tool in point-of-care devices to detect hematological diseases in clinical scenarios.

Detection of clot formation & lysis In-Vitro using high frequency photoacoustic imaging & frequency analysis

Clotting is a physiological process that prevents blood loss after injury. An imbalance in clotting factors can lead to lethal consequences such as exsanguination or inappropriate thrombosis. Clinical methods to monitor clotting and fibrinolysis typically measure the viscoelasticity of whole blood or optical density of plasma over time. Though these methods provide insights into clotting and fibrinolysis, they require milliliters of blood which can worsen anemia or only provide partial information. To overcome these limitations, a high-frequency photoacoustic (HFPA) imaging system was developed to detect clotting and lysis in blood. Clotting was initiated in vitro in reconstituted blood using thrombin and lysed with urokinase plasminogen activator. Frequency spectra measured using HFPA signals (10-40 MHz) between non-clotted blood and clotted blood differed markedly, allowing tracking of clot initiation and lysis in volumes of blood as low as 25 µL/test. HFPA imaging shows potential as a point-of-care examination of coagulation and fibrinolysis.

Biomedical Application of Photoacoustics: A Plethora of Opportunities

The photoacoustic (PA) technique is a non-invasive, non-ionizing hybrid technique that exploits laser irradiation for sample excitation and acquires an ultrasound signal generated due to thermoelastic expansion of the sample. Being a hybrid technique, PA possesses the inherent advantages of conventional optical (high resolution) and ultrasonic (high depth of penetration in biological tissue) techniques and eliminates some of the major limitations of these conventional techniques. Hence, PA has been employed for different biomedical applications. In this review, we first discuss the basic physics of PA. Then, we discuss different aspects of PA techniques, which includes PA imaging and also PA frequency spectral analysis. The theory of PA signal generation, detection and analysis is also detailed in this work. Later, we also discuss the major biomedical application area of PA technique.

Monitoring peripheral hemodynamic response to changes in blood pressure via photoacoustic imaging

Chronic wounds and amputations are common in chronic kidney disease patients needing hemodialysis (HD). HD is often complicated by drops in blood pressure (BP) called intra-dialytic hypotension. Whether intra-dialytic hypotension is associated with detectable changes in foot perfusion, a risk factor for wound formation and impaired healing remains unknown. Photoacoustic (PA) imaging is ideally suited to study perfusion changes. We scanned the feet of 20 HD and 11 healthy subjects. HD patients were scanned before and after a dialysis session whereas healthy subjects were scanned twice at rest and once after a 10 min exercise period while BP was elevated. Healthy (r = 0.70, p < 0.0001) and HD subjects (r = 0.43, p < 0.01) showed a significant correlation between PA intensity and systolic BP. Furthermore, HD cohort showed a significantly reduced PA response to changes in BP compared to the healthy controls (p < 0.0001), showing that PA can monitor hemodynamic changes due to changes in BP.

Photoacoustic graphic equalization and application in characterization of red blood cell aggregates

A photoacoustic (PA) graphic equalization (PAGE) algorithm was developed to characterize the relative size of optical absorbing aggregates. This technique divides the PA signal into frequency bands related to different-sized optical absorbers. Simulations of a material containing optical absorbing microparticles of varying size were used to assess PAGE performance. Experiments were performed on phantom materials containing microspheres of varying size and concentration. Additional experiments were performed using tubes with fresh clotting blood. PA data was obtained using a Vevo LAZR-X system (FUJIFILM VisualSonics Inc). PAGE imaging of phantoms with varying-sized optical absorbers found a 1.5-fold difference in mean image intensity (p < 0.001). Conversely, PA images from these same materials exhibited no intensity changes (p = 0.68). PAGE imaging results from clotting blood exhibited differences for clot sizes in the range 0.30-0.64 mm (p < 0.001). In summary, PAGE imaging can distinguish optical absorbing aggregates of varying size.

Quantification of number density of random microstructure from a photoacoustic signal by using Nakagami statistics

Tissue microstructure characterization is a valuable tool in diagnosis and staging of many diseases. In this study, we propose a photoacoustic Nakagami statistics method to noninvasively evaluate the number density of random microstructure. The Nakagami parameters are acquired by fitting the photoacoustic signal envelope histogram with Nakagami distribution function. Theoretical calculations and phantom experiments demonstrate that the Nakagami shape parameter is only related to the number density of random microstructure and monotonically increases with the number density. Based on this finding, we propose a photoacoustic tomography modality with the imaging contrast of the Nakagami shape parameter. Experiments show that the proposed method can provide more comprehensive and accurate description of tissue microstructure.

Whole-Cell Photoacoustic Sensor Based on Pigment Relocalization

Photoacoustic (optoacoustic) imaging can extract molecular information with deeper tissue penetration than possible by fluorescence microscopy techniques. However, there is currently still a lack of robust genetically controlled contrast agents and molecular sensors that can dynamically detect biological analytes of interest with photoacoustics. In a biomimetic approach, we took inspiration from cuttlefish who can change their color by relocalizing pigment-filled organelles in so-called chromatophore cells under neurohumoral control. Analogously, we tested the use of melanophore cells from Xenopus laevis, containing compartments (melanosomes) filled with strongly absorbing melanin, as whole-cell sensors for optoacoustic imaging. Our results show that pigment relocalization in these cells, which is dependent on binding of a ligand of interest to a specific G protein-coupled receptor (GPCR), can be monitored in vitro and in vivo using photoacoustic mesoscopy. In addition to changes in the photoacoustic signal amplitudes, we could furthermore detect the melanosome aggregation process by a change in the frequency content of the photoacoustic signals. Using bioinspired engineering, we thus introduce a photoacoustic pigment relocalization sensor (PaPiReS) for molecular photoacoustic imaging of GPCR-mediated signaling molecules.

In vitro photoacoustic spectroscopy of pulsatile blood flow: Probing the interrelationship between red blood cell aggregation and oxygen saturation

We investigate the optical wavelength dependence in quantitative photoacoustic (QPA) assessment of red blood cell (RBC) aggregation and oxygen saturation (sO₂ ) during pulsatile blood flow. Experimentally, the pulsatile flow was imaged with a 700 to 900 nm laser using the VevoLAZR. Theoretically, the photoacoustic (PA) signals were computed based on a Green's function integrated with a Monte Carlo simulation of radiant fluence. The pulsatile flow created periodic conditions of RBC aggregation/nonaggregation, altering the aggregate size, and, in turn, the sO₂ . The dynamic range, DR (a metric of change in PA power) from 700 to 900 nm for nonaggregated RBCs, was 5 dB for both experiment and theory. A significant difference in the DR for aggregated RBCs was 1.5 dB between experiment and theory. Comparing the DR at different wavelengths, the DR from nonaggregated to aggregated RBCs at 700 nm was significantly smaller than that at 900 nm for both experiment (4.0 dB < 7.1 dB) and theory (5.3 dB < 9.0 dB). These results demonstrate that RBC aggregation simultaneously affects the absorber size and the absorption coefficient in photoacoustic imaging (PAI) of pulsatile blood flow. This investigation elucidates how QPA spectroscopy can be used for probing hemodynamics and oxygen transport by PAI of blood flow.

Quantitative Measurement of Erythrocyte Aggregation as a Systemic Inflammatory Marker by Ultrasound Imaging: A Systematic Review

This systematic review is aimed at answering two questions: (i) Is erythrocyte aggregation a useful biomarker in assessing systemic inflammation? (ii) Does quantitative ultrasound imaging provide the non-invasive option to measure erythrocyte aggregation in real time? The search was executed through bibliographic electronic databases CINAHL, EMB Review, EMBASE, MEDLINE, PubMed and the grey literature. The majority of studies correlated elevated erythrocyte aggregation with inflammatory blood markers for several pathologic states. Some studies used "erythrocyte aggregation" as an established marker of systemic inflammation. There were limited but promising articles regarding the use of quantitative ultrasound spectroscopy to monitor erythrocyte aggregation. Similarly, there were limited studies that used other ultrasound techniques to measure systemic inflammation. The quantitative measurement of erythrocyte aggregation has the potential to be a routine clinical marker of inflammation as it can reflect the cumulative inflammatory dynamics in vivo, is relatively simple to measure, is cost-effective and has a rapid turnaround time. Technologies like quantitative ultrasound spectroscopy that can measure erythrocyte aggregation non-invasively and in real time may offer the advantage of continuous monitoring of the inflammation state and, thus, may help in rapid decision making in a critical care setup.

Extended photoacoustic transport model for characterization of red blood cell morphology in microchannel flow

The dynamic response behavior of red blood cells holds the key to understanding red blood cell related diseases. In this regard, an understanding of the physiological functions of erythrocytes is significant before focusing on red blood cell aggregation in the microcirculatory system. In this work, we present a theoretical model for a photoacoustic signal that occurs when deformed red blood cells pass through a microfluidic channel. Using a Green's function approach, the photoacoustic pressure wave is obtained analytically by solving a combined Navier-Stokes and photoacoustic equation system. The photoacoustic wave expression includes determinant parameters for the cell deformability such as plasma viscosity, density, and red blood cell aggregation, as well as involving laser parameters such as beamwidth, pulse duration, and repetition rate. The effects of aggregation on blood rheology are also investigated. The results presented by this study show good agreements with the experimental ones in the literature. The comprehensive analytical solution of the extended photoacoustic transport model including a modified Morse type potential function sheds light on the dynamics of aggregate formation and demonstrates that the profile of a photoacoustic pressure wave has the potential for detecting and characterizing red blood cell aggregation.

In Vivo Imaging of Microvasculature during Anesthesia with High-Resolution Photoacoustic Microscopy

Anesthesia monitoring is extremely important in improving the quality of anesthesia and ensuring the safety of patients in operation. Photoacoustic microscopy (PAM) is proposed to in vivo image the skin microvasculature of 10 nude mice undergoing general anesthesia by using the isoflurane gas with a concentration of 3%. Benefiting from strong optical absorption of hemoglobin, PAM has good contrast and high resolution in mapping of microvasculature. A series of high quality images can clearly reveal the subtle changes of capillaries in morphology over time. Two indices, vessel intensity and vessel density, are extracted from these images to measure the microvasculature quantitatively. The imaging results show that the vessel intensity and density are increased over time. After 65 min, the vessel intensity increased 42.7 ± 8.6% and the density increased 28.6 ± 12.2%. These indices extracted from photoacoustic images accurately reflect the greater blood perfusion undergoing general anesthesia. Additionally, abnormal reductions of vessel intensity and density are also observed as overtime anesthesia. This preclinical study suggests that PAM holds potential to monitor anesthesia by imaging the skin microvasculature.

Photoacoustic signal characterization of cancer treatment response: Correlation with changes in tumor oxygenation

Frequency analysis of the photoacoustic radiofrequency signals and oxygen saturation estimates were used to monitor the in-vivo response of a novel, thermosensitive liposome treatment. The liposome encapsulated doxorubicin (HaT-DOX) releasing it rapidly (<20 s) when the tumor was exposed to mild hyperthermia (43 °C). Photoacoustic imaging (VevoLAZR, 750/850 nm, 40 MHz) of EMT-6 breast cancer tumors was performed 30 min pre- and post-treatment and up to 7 days post-treatment (at 2/5/24 h timepoints). HaT-DOX-treatment responders exhibited on average a 22% drop in oxygen saturation 2 h post-treatment and a decrease (45% at 750 nm and 73% at 850 nm) in the slope of the normalized PA frequency spectra. The spectral slope parameter correlated with treatment-induced hemorrhaging which increased the optical absorber effective size via interstitial red blood cell leakage. Combining frequency analysis and oxygen saturation estimates differentiated treatment responders from non-responders/control animals by probing the treatment-induced structural changes of blood vessel.

A portable microfluidic system for rapid measurement of the erythrocyte sedimentation rate

The erythrocyte sedimentation rate (ESR) is a frequently used 30 min or 60 min clinical test for screening of several inflammatory conditions, infections, trauma, and malignant diseases, as well as non-inflammatory conditions including prostate cancer and stroke. Erythrocyte aggregation (EA) is a physiological process where erythrocytes form face-to-face linear structures, called rouleaux, at stasis or low shear rates. In this work, we proposed a method for ESR measurement from EA. We developed a microfluidic opto-electro-mechanical system, using which we experimentally showed a significant correlation (R² = 0.86) between ESR and EA. The microfluidic system was shown to measure ESR from EA using fingerprick blood in 2 min. 40 μl of whole blood is filled in a disposable polycarbonate cartridge which is illuminated with a near infrared emitting diode. Erythrocytes were disaggregated under the effect of a mechanical shear force using a solenoid pinch valve. Following complete disaggregation, transmitted light through the cartridge was measured using a photodetector for 1.5 min. The intensity level is at its lowest at complete disaggregation and highest at complete aggregation. We calculated ESR from the transmitted signal profile. We also developed another microfluidic cartridge specifically for monitoring the EA process in real-time during ESR measurement. The presented system is suitable for ultrafast, low-cost, and low-sample volume measurement of ESR at the point-of-care.

Simultaneous assessment of red blood cell aggregation and oxygen saturation under pulsatile flow using high-frequency photoacoustics

We investigate the feasibility of photoacoustic (PA) imaging for assessing the correlation between red blood cell (RBC) aggregation and the oxygen saturation (sO2) in a simulated pulsatile blood flow system. For the 750 and 850 nm illuminations, the PA amplitude (PAA) increased and decreased as the mean blood flow velocity decreased and increased, respectively, at all beat rates (60, 120 and 180 bpm). The sO2 also cyclically varied, in phase with the PAA for all beat rates. However, the linear correlation between the sO2 and the PAA at 850 nm was stronger than that at 750 nm. These results suggest that the sO2 can be correlated with RBC aggregation induced by decreased mean shear rate in pulsatile flow, and that the correlation is dependent on the optical wavelength. The hemodynamic properties of blood flow assessed by PA imaging may be used to provide a new biomarker for simultaneous monitoring blood viscosity related to RBC aggregation, oxygen delivery related to the sO2 and their clinical correlation.

Optical tweezers study of red blood cell aggregation and disaggregation in plasma and protein solutions

Kinetics of optical tweezers (OT)-induced spontaneous aggregation and disaggregation of red blood cells (RBCs) were studied at the level of cell doublets to assess RBC interaction mechanics. Measurements were performed under in vitro conditions in plasma and fibrinogen and fibrinogen + albumin solutions. The RBC spontaneous aggregation kinetics was found to exhibit different behavior depending on the cell environment. In contrast, the RBC disaggregation kinetics was similar in all solutions qualitatively and quantitatively, demonstrating a significant contribution of the studied proteins to the process. The impact of the study on assessing RBC interaction mechanics and the protein contribution to the reversible RBC aggregation process is discussed.

Acoustic resolution photoacoustic Doppler velocimetry in blood-mimicking fluids

Photoacoustic Doppler velocimetry provides a major opportunity to overcome limitations of existing blood flow measuring methods. By enabling measurements with high spatial resolution several millimetres deep in tissue, it could probe microvascular blood flow abnormalities characteristic of many different diseases. Although previous work has demonstrated feasibility in solid phantoms, measurements in blood have proved significantly more challenging. This difficulty is commonly attributed to the requirement that the absorber spatial distribution is heterogeneous relative to the minimum detectable acoustic wavelength. By undertaking a rigorous study using blood-mimicking fluid suspensions of 3 μm absorbing microspheres, it was discovered that the perceived heterogeneity is not only limited by the intrinsic detector bandwidth; in addition, bandlimiting due to spatial averaging within the detector field-of-view also reduces perceived heterogeneity and compromises velocity measurement accuracy. These detrimental effects were found to be mitigated by high-pass filtering to select photoacoustic signal components associated with high heterogeneity. Measurement under-reading due to limited light penetration into the flow vessel was also observed. Accurate average velocity measurements were recovered using "range-gating", which furthermore maps the cross-sectional velocity profile. These insights may help pave the way to deep-tissue non-invasive mapping of microvascular blood flow using photoacoustic methods.

Theoretical and experimental study of spectral characteristics of the photoacoustic signal from stochastically distributed particles

Photoacoustic imaging is an emerging technique which inherits the merits of optical imaging and ultrasonic imaging. However, classical photoacoustic imaging mainly makes use of the time-domain parameters of signals. In contrast to previous studies, we theoretically investigate the spectral characteristics of the photoacoustic signal from stochastic distributed particles. The spectral slope is extracted and used for describing the spectral characteristics of the photoacoustic signal. Both Gaussian and spherical distributions of optical absorption in particles are considered. For both situations, the spectral slope is monotonically decreased with the increase of particle size. In addition, the quantitative relationship between the spectral slope and the imaging system factors, including the laser pulse envelope, directivity of ultrasound transducer, and signal bandwidth, are theoretically analyzed. Finally, an idealized phantom experiment is performed to validate the analyses and examine the instrument independent of the spectral slope. This work provides a theoretical framework and new experimental evidence for spectrum analysis of the photoacoustic signal. This could be helpful for quantitative tissue evaluation and imaging based on the spectral parameters of the photoacoustic signal.

A simulation study on the quantitative assessment of tissue microstructure with photoacoustics

A detailed derivation of a quantity, defined as the acoustic power per unit solid angle far from the illuminated volume divided by the intensity of the incident light beam and termed as differential photoacoustic (PA) cross section, is presented. The expression for the differential PA cross section per unit absorbing volume retains two terms, namely, the coherent and the incoherent parts. The second part based on a correlation model can be employed to analyze the PA signal power spectrum for tissue characterization. The performances of the fluid sphere, Gaussian, and exponential correlation models in assessing the mean size and the variance in the optical absorption coefficients of absorbers were investigated by performing in silico experiments. It was possible to evaluate diameters of solid spherical absorbers with radii ≥ 20 μm with an accuracy of 10% for an analysis bandwidth of 5 to 50 MHz using the first two correlation models. The accuracy of estimation was about 22% for fluid spheres mimicking erythrocytes for the third correlation model for an analysis bandwidth of 5 to 100 MHz. The extracted values of average variance in the optical absorption coefficients demonstrated good correlation with the nominal values. This study suggests that the method presented here may be developed as a potential tissue characterization tool.

Photoacoustic imaging of nanoparticle- containing cells using single-element focused transducer: a simulation study

A new theoretical approach for photoacoustic (PA) image simulation of an ensemble of cells with endocytosed gold nanoparticles is presented. Each cell was approximated as a fluid sphere and suspended in a nonabsorbing fluid medium. It was assumed that the cellular optical absorption coefficient changed greatly because of endocytosis of nanoparticles; however, thermophysical parameters remained unchanged because nanoparticles occupied negligible intracellular volume. A frequency-domain method was used to obtain a PA signal from a single cell and resultant signal detected by a focused single-element transducer was evaluated by convolving signals from many cells with the spatial impulse response function of the receiver. The proposed model was explored to simulate PA images of numerical phantoms. It was observed that features of the phantoms are retained precisely in those simulated images. Also, speckles in PA images are significantly suppressed because of strong boundary buildup when cells are bounded to a region. Nevertheless, speckle visibility increases when cells are not bounded to a region. This approach may be developed as a realistic simulation tool for PA imaging of tissue medium utilizing its cellular feature.

Computational modeling of photoacoustic signals from mixtures of melanoma and red blood cells

A theoretical approach to model photoacoustic (PA) signals from mixtures of melanoma cells (MCs) and red blood cells (RBCs) is discussed. The PA signal from a cell approximated as a fluid sphere was evaluated using a frequency domain method. The tiny signals from individual cells were summed up obtaining the resultant PA signal. The local signal to noise ratio for a MC was about 5.32 and 5.40 for 639 and 822 nm illuminations, respectively. The PA amplitude exhibited a monotonic rise with increasing number of MCs for each incident radiation. The power spectral lines also demonstrated similar variations over a large frequency range (5-200 MHz). For instance, spectral intensity was observed to be 5.5 and 4.0 dB greater at 7.5 MHz for a diseased sample containing 1 MC and 22,952 RBCs than a normal sample composed of 22,958 RBCs at those irradiations, respectively. The envelope histograms generated from PA signals for mixtures of small numbers of MCs and large numbers of RBCs seemed to obey pre-Rayleigh statistics. The generalized gamma distribution found to facilitate better fits to the histograms than the Rayleigh and Nakagami distributions. The model provides a means to study PAs from mixtures of different populations of absorbers.

Probing red blood cell morphology using high-frequency photoacoustics

A method that can rapidly quantify variations in the morphology of single red blood cells (RBCs) using light and sound is presented. When irradiated with a laser pulse, an RBC absorbs the optical energy and emits an ultrasonic pressure wave called a photoacoustic wave. The power spectrum of the resulting photoacoustic wave contains distinctive features that can be used to identify the RBC size and morphology. When particles 5-10 μm in diameter (such as RBCs) are probed with high-frequency photoacoustics, unique periodically varying minima and maxima occur throughout the photoacoustic signal power spectrum at frequencies >100 MHz. The location and distance between spectral minima scale with the size and morphology of the RBC; these shifts can be used to quantify small changes in the morphology of RBCs. Morphological deviations from the normal biconcave RBC shape are commonly associated with disease or infection. Using a single wide-bandwidth transducer sensitive to frequencies between 100 and 500 MHz, we were able to differentiate healthy RBCs from irregularly shaped RBCs (such as echinocytes, spherocytes, and swollen RBCs) with high confidence using a sample size of just 21 RBCs. As each measurement takes only seconds, these methods could eventually be translated to an automated device for rapid characterization of RBC morphology and deployed in a clinical setting to help diagnose RBC pathology.

Photoacoustic pulse wave forming along the rotation axis of an ellipsoid droplet: a geometric calculation study

A geometric calculation method is developed to study the pulsed photoacoustic wave forming of an arbitrarily shaped droplet. It is found that for an ellipsoid droplet, either a prolate ellipsoid or an oblate ellipsoid, strict analytical formulas for describing the wave profile developed along the rotation axis can be derived. The results show intriguing differences compared to those of a sphere droplet in terms of the multiple geometric parameters being in effect, the pulse wave profile variant, and the existing of unlimited points of infinite tensile pressure.

Computational investigation on the photoacoustics of malaria infected red blood cells

A computer simulation study on the possibility of using photoacoustic (PA) technique to differentiate intraerythrocytic stages of malarial parasite is reported. This parasite during its development substantially converts hemoglobin into hemozoin. This conversion is expected to alter the cellular absorption leading to changes in the PA emission of a red blood cell (RBC) at certain incident optical wavelengths. The PA signals from blood samples corresponding to ring, trophozoite and schizont stages were computed and compared with that of normal blood. A Monte Carlo algorithm was implemented generating random locations of RBCs in 3D to simulate blood samples. The average PA amplitude for wide bandwidth signals decreases for 434 nm incident radiation, but increases for 700 nm as the parasite matures. The spectral power at 7.5 MHz for the blood sample at the schizont stage compared to the normal blood is nearly reduced by 6 dB and enhanced by 22 dB at those incident wavelengths, respectively. Bandlimited signals for transducers of 15 and 50 MHz center frequencies were studied and found to exhibit similar characteristics. The presence of hemozoin inside the cells was examined and an excellent estimation was made. The simulation results suggest that intraerythrocytic stages of malarial parasite may be assessed using the PA technique.