Understanding Standardized Uptake Values Biology Essay

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This project is a statistical study of 80 patients data recorded by Singapore General Hospital on Positron Emission Tomography/Computed Tomography scans. The data collected concentrates on 4 different organs mainly Liver, Spleen, Bone Marrow and Brain. However, this report would purely focus on the statistical study of the Brain (frontal, parietal and occipital lobes).

It is understood from many sources that solely studying and referring to Standard Uptake Values (SUV) of a patient after thorough PET scan may not be reliable due to many factors affecting the results. The possible factors that may affect the results are blood glucose level, age, gender and weight of patient [2]. Doctors and Radiologists are only proficient in this field after years of experience reading and analyzing PET scan results. This study hopes to achieve in modelling the data diligently and provide doctors a better understanding of how individual factors may affect SUV.

Project objectives

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To study the correlation between the parameters of the patients and standard uptake values. Discuss the possible off variances and possible causes of the discrepancies. With the knowledge of statistical methods and advanced mathematics to derive a mathematical model on study to assist doctors for better analysis on patients in the future.

Background research

Bio-imaging

Bio-imaging is a visual representation of a measurable property inside a human body which is always associated with medical treatment analysis. The technology emerged only recently with the help of advanced digital photography and allowed researchers to venture into many new bio-imaging techniques. Radiography, Magnetic Resonance Imaging, Nuclear Medicine and Tomography are one of the many imaging techniques developed over the years.

Nuclear Medicine

Nuclear Medicine consists of the combination of radioactive solution and bio-imaging technique to display information of the internal structure of a human body. Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) are such techniques that are categorized as nuclear medicine for internal imaging without invasive measures.

Prior scanning, a radioactive substance is injected into the subject or patient. Radioactive solutions that are injected are not very intensely radioactive that will cause harm in the patient's body. Nitrogen-13, Carbon-11, Fluorine-18 and Oxygen-15 are one of the few radioactive atoms which are attached to solutions. These radioactive atoms have low decay time allowing it to be a trivial radioactive solution for injection.

Positron Emission Tomography/Computed Tomography

Positron Emission Tomography (PET) is a bio-imaging technique that concentrates and exhibits the cell activity in a particular region of the body. It assists in displaying the metabolic activity in various organs. Doctors are able to visually notice the malignancies on regions that show concentration of fluorodeoxyglucose (FDG) annihilation which are color-coded. Computed Tomography is another non-invasive technique to display the bodily structure of the tested subject. These two techniques, PET and CT, are merged together as shown in figure 1 as one functional radiology system that helps radiologists and doctors to better understand tested subject.

http://medicineworld.org/images/blogs/pet-ct-scanner-41234692.jpg

Figure

Working Principles of PET

Fluorodeoxyglucose is a radioactive solution that consists of the fluorine-18 radionuclide. Fluorine-18 radionuclide is produced by a particle accelerator that forcefully sends hydrogen ions to Oxygen-18 supplemented water molecules transforming it into hydrogen fluoride as shown in equation (1). Unstable fluoride-18 has a half-life of 110 minutes[3] and decays by discharging positrons, equation (2). The discharged positron (β+) shortly reacts with electrons to undergo annihilation.

…………………… (1)

…………………………………....…. (2)

Figure 2 shows a simple diagram on the decay of unstable fluoride and the annihilation process followed by releasing 2 opposite flowing photons. Positron Emission Tomography is basically the detection of fluorine-18 annihilation or positron decay and placing these detection points on the body map based on coincidence matches. The gamma rays emitted by the annihilation is detected by the multiple rings of detectors in the system. These detectors are also known as photomultiplier or scintillator crystals.

Figure - Introduction to PETCT

Figure - Annihilation detectionsPatient will be injected with fluorodeoxyglucose at least one hour prior to the PET scan. One hour duration is to allow the glucose solution to settle in the body. The scintillator crystals are located in a donut shaped-like structure. Patient is elevated and moved in through the structure. During this movement, the scanning already takes place and detects annihilation photons from the patient's body.http://static.ddmcdn.com/gif/nuclear-medicine-brain.gif

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The directional flow of these annihilation photons or rather gamma ray emission would be detected by the scintillator crystals. This is then translated into 2D and 3D image for further analysis. As shown in figure 3 the gamma rays are collected as coincidence detection and assembled together to display on screen.

Standardized uptake values

Standardized Uptake Values (SUV) are numerical representation of how one can understand the amount of FDG concentration on a specified region. A typical SUV calculation formula is shown below (3). SUV is calculated based on the activity concentration in the region of interest divided by the amount of dose injected divided by the body weight[5]. SUV are currently used to differ between normal values and absurd values that will prove malignancy in a particular organ.

………..(3)

Other than visually analyzing the PET scan image, radiologist and doctors do rely on SUV for further evidence to state that a particular organ is exploited with cancerous cells. However, many other research study has mentioned that solely relying on standard uptake values may not be reliable. There are factors affecting the SUV such as the varying body weight, age, gender, blood glucose level and how different organs react to glucose uptake [2].

Human Organ - Brain

This research is to solely concentrate on the standard uptake values within the region of the brain. The brain is one of the most crucial and complicated organ in the human body which assists in tasks an individual does. It consists of a few sections that is catered for its ideal functions. All the nerves in the body is connected to the brain which is also known as the central nervous system. As shown in figure 4 there are frontal, parietal, occipital and temporal lobes that has their individual functions to collectively serve the human body.

Frontal lobe is commonly known as the most important part of the brain. It defines personality development, language skills, decision-making acts and emotions. Parietal lobe is usually associated with senses which incorporates nerves signals from the body to the brain. It also helps to process visual signals and bodily senses. The Occipital lobe is mainly associated with the visual interpretation and the distinguishing the color ranges of the views.

http://webspace.ship.edu/cgboer/brainlobes.gif

Figure - Sections of the brain

Common uses of PET scan on Brain

The body utilizes glucose for energy and almost a quarter of it is absorbed in the brain. The human brain absorbs glucose in order to function consistently as the neurons get active. The radioactive solution, upon injected into patient's body, will work during the PET scan to show activity levels in the brain. However patients with low level of activity regions in specific sectors of the brain may depict a diagnosis of Alzheimer's disease or dementia. The figure below shows the difference in activity levels between patient 'E' diagnosed with Alzheimer's disease and normal patient 'F' without any disease. High activity levels on sectors may also depict cancerous cell activity.

Figure 5