Medical Diagnostic Procedures Research Articles

Evaluating the X-ray-Shielding Performance of Graphene-Oxide-Coated Nanocomposite Fabric.

Exposure to ionizing radiation (IR) during diagnostic medical procedures brings certain risks, especially when experiencing recurrent exposures. The fabrication of nano-based composites, doped with different nanoparticles, have been suggested as effective shielding materials to replace conventional lead-based ones in material sciences and nanotechnology. In this study, commercially available fabrics, used to produce scrubs and gowns for clinical staff, are modified utilizing graphene oxide (GO) nanoparticles using a layer-by-layer (LBL) technique. GO was obtained from graphite through environmentally friendly technology by using a modified–improved Hummers’ method without NaNO3. Lightweight, flexible, air- and water-permeable shielding materials are produced that are wearable in all-day clinical practice. The nanoparticles are kept to a minimum at 1 wt%; however, utilizing the LBL technique they are distributed evenly along the fibers of the fabrics to achieve as much shielding effect as possible. The evaluation of samples is accomplished by simulating real-time routine clinical procedures and the radiographic programs and devices used daily. The GO-coated nanocomposite fabrics demonstrated promising results for X-ray shielding.

360º optoacoustic capsule endoscopy at 50 Hz for esophageal imaging

Gastrointestinal (GI) endoscopy is a common medical diagnostic procedure used for esophageal cancer detection. Current emerging capsule optoacoustic endoscopes, however, suffer from low pulse repetition rates and slow scanning units limit attainable imaging frame rates. Consequently, motion artifacts result in inaccurate spatial mapping and misinterpretation of data. To overcome these limitations, we report a 360º, 50 Hz frame rate, distal scanning capsule optoacoustic endoscope. The translational capability of the instrument for human GI tract imaging was characterized with an Archimedean spiral phantom consisting of twelve 100 µm sutures, a stainless steel mesh with a pitch of 3 mm and an ex vivo pig esophagus sample. We estimated an imaging penetration depth of ~0.84 mm in vivo by immersing the mesh phantom in intralipid solution to simulate light scattering in human esophageal tissue and validated our findings ex vivo using pig esophagus. This proof-of-concept study demonstrates the translational potential of the proposed video-rate endoscope for human GI tract imaging.

Development of Nucleic Acid Based Diagnostic Methods and their Implications in Oral Medicine Practice

Disease identification methods based on nucleic acids are commonly employed in medical diagnostic procedures. Nucleic acid detection is a vital technique that identifies specific nucleotide sequences, hence indicating the presence of a pathogen or the onset of an unhealthy condition. The techniques based on them are constantly advancing and there is a certain drive in the scientific community to devise tests that are more rapid, reliable, and economical. Advances in nucleic acid based diagnostics, for instance Polymerase Chain Reaction (PCR) and sequence alignment studies, have transformed the way clinical laboratories presently detect pathogens, allowing for rapid and effective response to infection therapy at an early phase. Nucleic acid detecting might actually be a linkage between oral and systemic diseases since persistent inflammation in the oral cavity is related with systemic diseases. The capacity to distinguish genetically between closely related disorders is especially crucial for bacterial or viral infections, which may rapidly evolve and produce new strains. Another advantage of infectious disease nucleic acid biomarkers being exogenous is that they may be discovered in the body shortly after infection. In principle, this allows for early detection and can be helpful in slowing or stopping disease transmission. This article reviews the evolutionary milestones of its current applications, emerging applications in oral diagnosis and future trends. Over the last decade, molecular biology has evolved at an accelerated pace, enabling the detection and management of a varied range of oral diseases. Understanding the numerous sequencing methodologies and genetic anomalies can assist in clinical application for improved disease diagnosis and prognosis.

The aspects of local allergic rhinitis in Polish children and adolescents.

Local allergic rhinitis (LAR) is one of the endotypes of rhinitis which occurs commonly in different age groups. To present the occurrence and characteristics of LAR in Polish children and adolescents. In the study protocol, three hundred sixty-one patients aged 5-17 with chronic rhinitis were included from 8 centres in Poland. Medical history and diagnostic procedures were performed with aeroallergens: skin prick tests, allergen-specific serum IgE and nasal provocation tests. In addition to LAR, allergic rhinitis (AR), dual allergic rhinitis (DUAL) and non-allergic rhinitis (NAR) were explored and compared. LAR was confirmed in 21% of patients, systemic allergic rhinitis (SAR) in 43.9%, DUAL in 9.4% and NAR in 33.9% of patients. Based on nasal provocation test (NPT), allergy to HDM prevailed in the LAR group (68%), grass in the SAR group (58%), and grass and HDM in the DUAL group (32% and 64%). Girls were prevalent in the LAR group, and severe rhinitis and asthma were more common than other endotypes (p < 0.05). LAR is a common disease in children and adolescents and is often associated with severe rhinitis and frequently coexists with asthma.

Risk factors of cancer: a review

Cancer has been known since BC., with rare incidence. At that time, some scientists tried to treat cancer, and some tried to find out the reason(s) behind the occurrence of cancer, and they put up many hypotheses. Nowadays, with all progression in medical technology and diagnostic methods, the causes of cancer remain unclear. But the causes of cancer can be an interaction between a person’s genetic factors and external carcinogens factors that can be divided into physical, chemical, and biological carcinogens. In this review, the risk factors of cancer were discussed.

A Multi-Feature Fusion Network for Pathological Identification of Tumor Cells

A novel multi-feature fusion neural network (MFNet) is proposed to address the lack of applicability of existing medical aid diagnostic methods for cross-site and cross-tissue cytopathic lesion screening. MFNet consists of a data-sharing layer, a detailed feature transfer branch, a microscopic identification branch, and an auxiliary loss function. The data-sharing layer converts data images into a feature matrix and extracts detailed elements such as cell morphology, contour, and texture. The microscopic recognition branch obtains multilevel elements by convolving the input elements in stages and fusing them, so that the network can focus on high-level semantic elements such as minor differences of cytopathy. The detail feature transfer branch transfers detail elements across layers and achieves cross-layer fusion with semantic elements. The auxiliary loss function enables the network feature classification capability to be enhanced. MFNet is experimentally compared with AlexNet, VGG-16, ResNet-50, and other models on the tumor cell datasets, and the results show that the proposed method can effectively improve the recognition accuracy.

Monte Carlo simulation of particle size separation in evaporating bi-dispersed colloidal droplets on hydrophilic substrates

Colloidal droplets are used in a variety of practical applications. Some of these applications require particles of different sizes. These include medical diagnostic methods, the creation of photonic crystals, the formation of supraparticles, and the production of membranes for biotechnology. A series of earlier experiments had shown the possibility of particle separation near the contact line, depending upon their size. A mathematical model has been developed to describe this process. Bi-dispersed colloidal droplets evaporating on a hydrophilic substrate are taken into consideration. A particle monolayer is formed near the periphery of such droplets due to the small value of the contact angle. The shape of the resulting deposit is associated with the coffee ring effect. The model takes into account both particle diffusion and transfers caused by capillary flow due to liquid evaporation. Monte Carlo simulations of such particle dynamics have been performed at several values of the particle concentration in the colloidal solution. The numerical results agree with the experimental observations, in which small particles accumulate nearer to the contact line than do the large particles. However, the particles do not actually reach the contact line but accumulate at a small distance from it. The reason for this is the surface tension acting on the particles in areas, where the thickness of the liquid layer is comparable to the particle size. Indeed, the same mechanism affects the observed separation of the small and large particles.

Radioactive nuclei forβ+γPET and theranostics: selected candidates

AbstractPositron emission tomography (PET) is an established medical diagnostic imaging method. Continuous improvements are aimed at refining image reconstruction, reducing the amount of radioactive tracer and combining with targeted therapy. Time-of-flight (TOF)-PET provides the localization of the tracer through improved time resolution, nuclear physics may contribute to this goal via selection of radioactive nuclei emitting additional γ-rays. This additional radiation, when properly detected, localizes the decay of the tracer at the line of response (LoR) determined by two detected 511 keV quanta. Selected candidates are presented. Some are particularly interesting, as they are strong candidates for theranostic applications.

Patient empowerment through a user-centered design of an electronic personal health record: a qualitative study of user requirements in chronic kidney disease

BackgroundTo improve chronic disease outcomes, self-management is an effective strategy. An electronic personal health record (ePHR) is a promising tool with the potential to support chronic patient’s education, counseling, and self-management. Fitting ePHRs within the daily practices of chronic care providers and chronic patients requires user-centered design approaches. We aimed to understand users’ needs and requirements in chronic kidney disease (CKD) care to consider in the design of an ePHR to facilitate its implementation, adoption, and use.MethodsA qualitative study was conducted in a major Iranian nephrology center including inpatient and outpatient settings in 2019. We conducted 28 semi-structured interviews with CKD patients, nurses, and adult nephrologists. To confirm or modify the requirements extracted from the interviews, a focus group was also held. Data were analyzed to extract especially those requirements that can facilitate implementation, adoption, and sustained use based on the PHR adoption model and the unified theory of acceptance and use of technology.ResultsParticipants requested an ePHR that provides access to up to date patient information, facilitates patient-provider communication, and increases awareness about patient individualized conditions. Participants expected a system that is able to cater to low patient e-health literacy and high provider workload. They requested the ePHR to include purposeful documentation of medical history, diagnostic and therapeutic procedures, tailored educational content, and scheduled care reminders. Messaging function, tailored educational content to individual patients’ conditions, and controlled access to information were highly valued in order to facilitate its implementation, adoption, and use.ConclusionsWe focused on the ePHR’s content and functionalities in the face of facilitators and/or barriers envisioned for its adoption in nephrology care. Designers and implementers should value CKD patients’ needs and requirements for self-management such as providing personalized education and counseling (on the basis of their condition and risk factors), health literacy, and disease progression levels. The socio-technical aspects of care also need further attention to facilitate ePHR’s adoption.

Abstract 9842: An Implemented Medical Mockup Modelling for Personalised Medicine and Surgery

Introduction: Virtual three-dimensional (3D) anatomical models can improve diagnostic and surgical medical procedures with a patient-specific approach. The advantage of these models, in opposition to CT scans or MRIs alone, is their unique ability to demonstrate anatomical spatial relationship with submillimetre accuracy. Methods: Starting from our platform Med3D VR Lab, we implemented, in the MMM project, a basic algorithm within a software, able to capture, from DICOM images (MRIs/CT scans), the cloud of points needed to build 3D images. Different areas of a tissue might have different radio-density levels. In these cases, we applied our patented algorithm to harmonize these values through a transformation matrix. Results: We created a VR Laboratory (via a supervised learned approach) to access the resulting 3D image. The user, by wearing a VR headset, can rotate and enlarge the heart’s model. By cutting the model with the scalpel tool, the user is able to see the interior of the 3D model. The sections of the heart are created according to the direction of the cut. Each section can be further cut into smaller sub-sections, and both sections and sub-sections can be saved for future use. Conclusions: We developed a software for the conversion of 2D cardiac images in 3D models, which can be further examined and sectioned in a VR environment. This technique could help cardiologists in refining diagnosis and surgeons in tailoring cardiac interventions on the basis of patients’ characteristics, thus reducing operating times and costs while also preventing possible complications in cardiac surgery- therefore allowing to precisely assess risks in advance. Moreover, our software, through the VR visor, allows patients to truly understand their clinical conditions, thus overcoming the drawbacks of expressing an informed consent based only on DICOM imaging: the patients themselves will be able to understand the risks and benefits of a given surgical operations or its alternatives.

Vascular Damage in the Aorta of Wild-Type Mice Exposed to Ionizing Radiation: Sparing and Enhancing Effects of Dose Protraction.

Simple SummaryThe circulatory system receives ionizing radiation at various dose rates. Here, we analyzed changes in the circulatory system of wild-type mice at six months after starting acute, intermittent or continuous irradiation with 5 Gy of photons. Irradiation had little effect on left ventricular function, heart weight, and kidney weight. In the aorta, acute exposure caused structural disorganizations and detachment of the aortic endothelium and intima-media thickening. These morphological changes were concomitant with increases in markers for profibrosis, fibrosis, proinflammation, and macrophages, along with decreases in markers for cell adhesion and vascular functionality in the aortic endothelium. Compared with acute exposure, the magnitude of such aortic changes was overall greater in 25 fractions, smaller in 100 fractions, and much smaller in chronic exposure. These findings suggest that dose protraction alters aortic vascular damage, in a way that is not a simple function of dose rate.During medical (therapeutic or diagnostic) procedures or in other settings, the circulatory system receives ionizing radiation at various dose rates. Here, we analyzed prelesional changes in the circulatory system of wild-type mice at six months after starting acute, intermittent, or continuous irradiation with 5 Gy of photons. Independent of irradiation regimens, irradiation had little impact on left ventricular function, heart weight, and kidney weight. In the aorta, a single acute exposure delivered in 10 minutes led to structural disorganizations and detachment of the aortic endothelium, and intima-media thickening. These morphological changes were accompanied by increases in markers for profibrosis (TGF-β1), fibrosis (collagen fibers), proinflammation (TNF-α), and macrophages (F4/80 and CD68), with concurrent decreases in markers for cell adhesion (CD31 and VE-cadherin) and vascular functionality (eNOS) in the aortic endothelium. Compared with acute exposure, the magnitude of such aortic changes was overall greater when the same dose was delivered in 25 fractions spread over 6 weeks, smaller in 100 fractions over 5 months, and much smaller in chronic exposure over 5 months. These findings suggest that dose protraction alters vascular damage in the aorta, but in a way that is not a simple function of dose rate.

Dealing with disability: challenges in Dutch health care of parents with a non-Western migration background and a child with a developmental disability

Purpose Parents of children with developmental disabilities who have a non-western migration background often experience unique challenges in foreign health care systems. This study aimed to describe these experiences to better understand these challenges and thereby improve health care provision. Method Twelve parents were interviewed using in-depth, semi-structured interviews. Our data was analysed, and themes were identified using open, selective, and axial coding. Results Multiple parents in our study had a different perception of what constitutes a “handicap”, may regard it as something that is very severe and highly stigmatized and will be less aware of the complex system of care professionals that aim to support them in the care for their child. Additionally, communication with care professionals may be complicated because of language differences and expectations about the division of roles and responsibilities between parents and professionals. This may result in lower involvement in health care. Conclusion As a result of cultural differences in the meaning, information and interaction about disabilities, non-western migrant parents will have a harder time coping with the diagnosis of their child’s disability and will experience more challenges with their involvement in health care. 1 Implications for Rehabilitation To be aware that non-western parents who are told their child has a disability are likely to experience more shame, fear of stigma and may have other definitions of disability than western parents. To pay specific attention to explain as much as possible about the causes, meaning and medical as well as societal future expectations for children with a disability to parents with another cultural background. To explore which knowledge parents have about their child's disability and the Dutch health care system, so that information and support can be personalized. To make sure there are translators present who can not only translate in the correct language but who can also explain commonly used terms for disabilities and other medical concepts, diagnostic procedures, and other specificities of the health care system of the host country to migrant parents. To psycho-educate parents with a migrant background that they are expected to be actively involved in the professional care for their child with a disability without this having negative consequences for the care of their child.

Check Only Once? Health Information Exchange between Competing Private Hospitals

Health check is essential in medical diagnostic procedures, so double-check becomes common if patients have physical examination/blood tests in one hospital but transfer to another hospital in the next period. To save patients’ costs, blockchain-based health information exchange for differentiated service is advocated but competing hospitals usually have incentive conflicts, especially those private hospitals who are most concerned with profitability. In this paper, we develop a two-period model where two private hospitals compete in both service quality and service charges. We formulate their tradeoffs towards health information exchange and find that interestingly, the two hospitals achieve incentive alignment when their profit loss in health check fee is significant and the service competition is intensified. We identify two driving forces, namely, the quality improvement effect and the price compensation effect, to interpret the rationality of the hospitals’ preferences of health information exchange.

Analytical temperature profiles for laser-irradiated gold nanorod immersed in an optically non-absorbing medium

Laser heating of gold nanorods immersed in an optically non-absorbing medium is important in both therapeutic and diagnostic medical procedures. For both continuous wave and pulsed lasers, we derive analytical temperature solutions by modeling a nanorod as a prolate spheroid. For the continuous wave laser irradiation, an exact analytical solution for the steady state heat transfer case using integer-degree Legendre function expansions in prolate spheroidal coordinates is presented. The steady state solution reveals that for the case of gold nanorod immersed in water, there is insignificant temperature variations on any single spheroidal surface that is coincident or confocal to the prolate spheroid surface, and the temperature only changes across spheroidal surfaces within the immediate surrounding water. This is found to be due to the very high thermal conductivity of gold which is more than a hundred-fold higher than that of water. The insight that the temperature rise is nearly invariant on any single spheroidal surface, along with a dimensional analysis, helps reduce the complexity of the heat equation in the unsteady regime of a pulsed laser illumination, and leads to a simple, lower dimensional model of unsteady heat equation, which takes into account the temporal dependency and spatial dependency in the direction across spheroidal surfaces. For the reduced unsteady heat equation, a simple, efficient, and insightful solution algorithm based on the Laplace transform and complex-degree Legendre functions is proposed. The maximum temperature and temperature profiles as functions of laser power, and nanorod geometries are obtained, revealing that for a fixed laser fluence and fixed nanorod mass, the more stretched nanorods yield higher temperatures in the spheroid and its immediate surroundings. In other words, more stretched nanorods are more efficient in converting the laser energy into localized, elevated temperatures. The obtained temperature solutions are useful in designing a parameter space for optimum therapeutic procedures for ablating cancer cells using high temperatures generated in the immediate vicinity of nanoparticles. The unsteady temperature solutions can also be used to obtain solutions to thermo-elastic models which are used to compute the photoacoustic signals that can, in turn, be used for cellular imaging and diagnostics.

Diagnostic chest X-rays and breast cancer risk among women with a hereditary predisposition to breast cancer unexplained by a BRCA1 or BRCA2 mutation

BackgroundDiagnostic ionizing radiation is a risk factor for breast cancer (BC). BC risk increases with increased dose to the chest and decreases with increased age at exposure, with possible effect modification related to familial or genetic predisposition. While chest X-rays increase the BC risk of BRCA1/2 mutation carriers compared to non-carriers, little is known for women with a hereditary predisposition to BC but who tested negative for a BRCA1 or BRCA2 (BRCA1/2) mutation.MethodsWe evaluated the effect of chest X-rays from diagnostic medical procedures in a dataset composed of 1552 BC cases identified through French family cancer clinics and 1363 unrelated controls. Participants reported their history of X-ray exposures in a detailed questionnaire and were tested for 113 DNA repair genes. Logistic regression and multinomial logistic regression models were used to assess the association with BC.ResultsChest X-ray exposure doubled BC risk. A 3% increased BC risk per additional exposure was observed. Being 20 years old or younger at first exposure or being exposed before first full-term pregnancy did not seem to modify this risk. Birth after 1960 or carrying a rare likely deleterious coding variant in a DNA repair gene other than BRCA1/2 modified the effect of chest X-ray exposure.ConclusionEver/never chest X-ray exposure increases BC risk 2-fold regardless of age at first exposure and, by up to 5-fold when carrying 3 or more rare variants in a DNA repair gene.Further studies are needed to evaluate other DNA repair genes or variants to identify those which could modify radiation sensitivity. Identification of subpopulations that are more or less susceptible to ionizing radiation is important and potentially clinically relevant.

FBG-Based Estimation of External Forces Along Flexible Instrument Bodies.

A variety of medical treatment and diagnostic procedures rely on flexible instruments such as catheters and endoscopes to navigate through tortuous and soft anatomies like the vasculature. Knowledge of the interaction forces between these flexible instruments and patient anatomy is extremely valuable. This can aid interventionalists in having improved awareness and decision-making abilities, efficient navigation, and increased procedural safety. In many applications, force interactions are inherently distributed. While knowledge of their locations and magnitudes is highly important, retrieving this information from instruments with conventional dimensions is far from trivial. Robust and reliable methods have not yet been found for this purpose. In this work, we present two new approaches to estimate the location, magnitude, and number of external point and distributed forces applied to flexible and elastic instrument bodies. Both methods employ the knowledge of the instrument’s curvature profile. The former is based on piecewise polynomial-based curvature segmentation, whereas the latter on model-based parameter estimation. The proposed methods make use of Cosserat rod theory to model the instrument and provide force estimates at rates over 30 Hz. Experiments on a Nitinol rod embedded with a multi-core fiber, inscribed with fiber Bragg gratings, illustrate the feasibility of the proposed methods with mean force error reaching 7.3% of the maximum applied force, for the point load case. Furthermore, simulations of a rod subjected to two distributed loads with varying magnitudes and locations show a mean force estimation error of 1.6% of the maximum applied force.

Mass spectrometry imaging technology and its application in breast cancer research

乳腺癌是女性最常见的恶性肿瘤,其发病率在世界范围内呈现上升趋势,是威胁女性健康的重要疾病之一。随着现代医学技术的快速发展,早期有效的诊断和筛查方法能够改善乳腺癌患者生存率和提高其生活质量。由于乳腺癌肿瘤具有非常显著的异质性,这对于诊断和筛查带来了较大困难,亟须在肿瘤演进时间信息中,继续引入生物分子的空间信息,从而对其异质性、肿瘤微环境等进行准确的追踪。质谱成像技术,可在免标记的前提下利用离子质荷比的特性发现生物组织中的各种分子,并研究这些分子的时间和空间信息,对其进行准确的定性、定量和空间定位。目前,通过质谱成像技术可直接获取药物及其代谢物、内源性代谢物、脂质、多肽和蛋白质等在组织中的空间分布信息,为肿瘤分子分型诊断和确认以及相关抗肿瘤药物的筛选提供了新的思路和研究方向。该综述以乳腺癌相关的生物样品制备和研究进展为主要内容,从小分子样本、大分子样本、石蜡包埋样本、基质喷涂方式、常用离子源等方面阐述质谱成像中样本制备的重要性以及样品制备过程中存在的难点问题。同时,以细胞模型、动物模型和临床肿瘤标本为研究对象,汇总了质谱成像技术在乳腺癌方面的应用进展,并进行了展望,为开展癌症精准分型研究和药物药效的快速筛查提供了重要依据。

On the origin and correction for inner filter effects in fluorescence. Part II: secondary inner filter effect -the proper use of front-face configuration for highly absorbing and scattering samples

Fluorescence is an established technology for studying molecular processes and molecular interactions. More recently fluorescence became a leading method for detection, sensing, medical diagnostics, biotechnology, imaging, DNA analysis, and gene expression. Consequently, precise and accurate measurements in various conditions have become more critical for proper result interpretations. Previously, in Part 1, we discussed inner filter effect type I, which is a consequence of the instrumental geometrical sensitivity factor and absorption of the excitation. In this part, we analyze inner filter effect type II and discuss the practical consequences for fluorescence measurements in samples of high optical density (absorbance/scattering). We consider both the standard square and front-face experimental configurations, discuss experimental approaches to limit/mitigate the effect and discuss methods for correcting and interpreting experimental results.

Establishing C. elegans as a Model for Studying the Bioeffects of Therapeutic Ultrasound

Ultrasound is widely used in diagnostic and therapeutic medical procedures and it is becoming an important tool in biomedical research. During exposure, as an ultrasound beam interacts with the tissues in its path, changes known as “bioeffects” can result. Animal studies have suggested that these changes can alter survival, movement, reproduction, development and learning in various species. Additional studies in animals could provide valuable information about the mechanisms of therapeutic ultrasound and may contribute to the development of additional exciting laboratory techniques. Therefore, we developed methods for exposing C. elegans nematode worms to ultrasound and observed that they exhibited exposure-dependent reductions in movement, fecundity and survival. These effects were prevented by polyvinyl alcohol, which suggested that cavitation was the main mechanism of damage. This work provides a foundation for capitalizing on the advantages of C. elegans as a model to thoroughly characterize ultrasound's bioeffects at the cellular and molecular levels.

Analysis of the applicability of the classical probabilistic parameters of the Monte Carlo algorithm for problems of light transport in turbid biological media with continuous absorption and discrete scattering

Simulation of light propagation by the statistical Monte Carlo (MC) method is widely used in many fields, especially in astrophysics, atmospheric optics, ocean optics, and nuclear medicine. In the optics of biological tissues, the MC method is used to simulate the luminous flux, which is formed during various medical therapeutic or diagnostic procedures inside a biological tissue and on its surface. In such calculations, the MC method is commonly considered as a reference one, which ensures an arbitrarily high accuracy with an increase in the number of ‘photons’. However, it can be shown that this is not always the case. In this paper, in the methodological aspect, the idealised one-dimensional problems of the transport theory for a turbid medium with continuous absorption and scattering and a turbid medium with discrete scatterers inside a continuously absorbing medium are considered. Their exact analytical solutions are presented and compared with the results of statistical modelling by the MC method. It is found that the use of classical probabilistic parameters for a medium with continuous absorption and scattering in the MC algorithm leads to a systematic method error in determining the values of radiation fluxes for biological media with discrete scattering, up to 10% for fluxes at the boundary in some cases. The causes of the error are discussed and it is shown how to modify the probabilistic parameters of the MC algorithm to eliminate it.