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74-511: The ultimate goal of molecular imaging is to be able to noninvasively monitor all of the biochemical processes occurring inside an organism in real time. Current research in molecular imaging involves cellular / molecular biology , chemistry , and medical physics , and is focused on: 1) developing imaging methods to detect previously undetectable types of molecules, 2) expanding the number and types of contrast agents available, and 3) developing functional contrast agents that provide information about

148-545: A magnetic flux of 1 weber (Wb) through a surface of one square meter is equal to a magnetic flux density of 1 tesla. That is, T = W b m 2 . {\displaystyle \mathrm {T={\dfrac {Wb}{m^{2}}}} .} Expressed only in SI base units , 1 tesla is: T = k g A ⋅ s 2 , {\displaystyle \mathrm {T={\dfrac {kg}{A{\cdot }s^{2}}}} ,} where A

222-420: A better understanding of the structure and function of cells. Many techniques commonly used to study cell biology are listed below: There are two fundamental classifications of cells: prokaryotic and eukaryotic . Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane-bound organelle . Prokaryotic cells are much smaller than eukaryotic cells, making them

296-431: A cell binds a molecule that is attached to the membrane of another cell. Endocrine signaling occurs through molecules secreted into the bloodstream. Paracrine signaling uses molecules diffusing between two cells to communicate. Autocrine is a cell sending a signal to itself by secreting a molecule that binds to a receptor on its surface. Forms of communication can be through: Cells are the foundation of all organisms and are

370-461: A cell lineage depends on the maintenance of cell division potential. This potential may be lost in any particular lineage because of cell damage, terminal differentiation as occurs in nerve cells, or programmed cell death ( apoptosis ) during development. Maintenance of cell division potential over successive generations depends on the avoidance and the accurate repair of cellular damage, particularly DNA damage . In sexual organisms, continuity of

444-463: A charged particle is not due to the charged particle's movement. This may be appreciated by looking at the units for each. The unit of electric field in the MKS system of units is newtons per coulomb, N/C, while the magnetic field (in teslas) can be written as N/(C⋅m/s). The dividing factor between the two types of field is metres per second (m/s), which is velocity. This relationship immediately highlights

518-428: A greater degree of objectivity to the study of these areas. One emerging technology is MALDI molecular imaging based on mass spectrometry . Many areas of research are being conducted in the field of molecular imaging. Much research is currently centered on detecting what is known as a predisease state or molecular states that occur before typical symptoms of a disease are detected. Other important veins of research are

592-505: A magnetic field of one tesla, at a speed of one metre per second (m/s), experiences a force with magnitude one newton (N), according to the Lorentz force law . That is, T = N ⋅ s C ⋅ m . {\displaystyle \mathrm {T={\dfrac {N{\cdot }s}{C{\cdot }m}}} .} As an SI derived unit , the tesla can also be expressed in terms of other units. For example,

666-473: A peptide probe that can binds to apoptotic and necrotic cells. A number of near-infrared (NIR) fluorophores have been employed for in vivo imaging, including Kodak X-SIGHT Dyes and Conjugates, Pz 247, DyLight 750 and 800 Fluors, Cy 5.5 and 7 Fluors, Alexa Fluor 680 and 750 Dyes, IRDye 680 and 800CW Fluors. Quantum dots, with their photostability and bright emissions, have generated a great deal of interest; however, their size precludes efficient clearance from

740-512: A potential strategy for the prevention and treatment of various disorders. Many of these disorders are prevented or improved by consuming polyphenol in the meal. As a result, natural compounds with the ability to modify the autophagy mechanism are seen as a potential therapeutic option. The creation of the double membrane (phagophore), which would be known as nucleation, is the first step in macro-autophagy. The phagophore approach indicates dysregulated polypeptides or defective organelles that come from

814-626: A sensitivity of around 10 mol/L to 10 mol/L which, compared to other types of imaging, can be very limiting. This problem stems from the fact that the difference between atoms in the high energy state and the low energy state is very small. For example, at 1.5 Tesla , a typical field strength for clinical MRI, the difference between high and low energy states is approximately 9 molecules per 2 million. Improvements to increase MR sensitivity include increasing magnetic field strength, and hyperpolarization via optical pumping, dynamic nuclear polarization or parahydrogen induced polarization . There are also

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888-532: A variety of signal amplification schemes based on chemical exchange that increase sensitivity. To achieve molecular imaging of disease biomarkers using MRI, targeted MRI contrast agents with high specificity and high relaxivity (sensitivity) are required. To date, many studies have been devoted to developing targeted-MRI contrast agents to achieve molecular imaging by MRI. Commonly, peptides, antibodies, or small ligands, and small protein domains, such as HER-2 affibodies, have been applied to achieve targeting. To enhance

962-431: A σ protein that assists only with initiation. For instance, in a process termed conjugation , the fertility factor allows the bacteria to possess a pilus which allows it to transmit DNA to another bacteria which lacks the F factor, permitting the transmittance of resistance allowing it to survive in certain environments. Eukaryotic cells are composed of the following organelles: Eukaryotic cells may also be composed of

1036-705: Is ampere , kg is kilogram , and s is second . Additional equivalences result from the derivation of coulombs from amperes (A), C = A ⋅ s {\displaystyle \mathrm {C=A{\cdot }s} } : T = N A ⋅ m , {\displaystyle \mathrm {T={\dfrac {N}{A{\cdot }m}}} ,} the relationship between newtons and joules (J), J = N ⋅ m {\displaystyle \mathrm {J=N{\cdot }m} } : T = J A ⋅ m 2 , {\displaystyle \mathrm {T={\dfrac {J}{A{\cdot }m^{2}}}} ,} and

1110-430: Is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. The theory behind PET is simple enough. First a molecule is tagged with a positron emitting isotope. These positrons annihilate with nearby electrons, emitting two 511 keV photons, directed 180 degrees apart in opposite directions. These photons are then detected by the scanner, which can estimate

1184-415: Is a branch of biology that studies the structure , function , and behavior of cells . All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and functioning of organisms. Cell biology is the study of the structural and functional units of cells. Cell biology encompasses both prokaryotic and eukaryotic cells and has many subtopics which may include

1258-722: Is a self-degradative mechanism that regulates energy sources during growth and reaction to dietary stress. Autophagy also cleans up after itself, clearing aggregated proteins, cleaning damaged structures including mitochondria and endoplasmic reticulum and eradicating intracellular infections. Additionally, autophagy has antiviral and antibacterial roles within the cell, and it is involved at the beginning of distinctive and adaptive immune responses to viral and bacterial contamination. Some viruses include virulence proteins that prevent autophagy, while others utilize autophagy elements for intracellular development or cellular splitting. Macro autophagy, micro autophagy, and chaperon-mediated autophagy are

1332-575: Is also known as the S-phase. During mitosis, which is also known as the M-phase, the segregation of the chromosomes occur. DNA, like every other molecule, is capable of undergoing a wide range of chemical reactions. Modifications in DNA's sequence, on the other hand, have a considerably bigger impact than modifications in other cellular constituents like RNAs or proteins because DNA acts as a permanent copy of

1406-519: Is controlled by the temporal activation of Cdks, which is governed by cyclin partner interaction, phosphorylation by particular protein kinases, and de-phosphorylation by Cdc25 family phosphatases. In response to DNA damage, a cell's DNA repair reaction is a cascade of signaling pathways that leads to checkpoint engagement, regulates, the repairing mechanism in DNA, cell cycle alterations, and apoptosis. Numerous biochemical structures, as well as processes that detect damage in DNA, are ATM and ATR, which induce

1480-424: Is generally used on samples of free cells or tissue fragments, in contrast to the pathology branch of histopathology , which studies whole tissues. Cytopathology is commonly used to investigate diseases involving a wide range of body sites, often to aid in the diagnosis of cancer but also in the diagnosis of some infectious diseases and other inflammatory conditions. For example, a common application of cytopathology

1554-456: Is possible. Above 900 nm, water absorption can interfere with signal-to-background ratio. Because the absorption coefficient of tissue is considerably lower in the near infrared (NIR) region (700-900 nm), light can penetrate more deeply, to depths of several centimeters. Fluorescent probes and labels are an important tool for optical imaging. Some researchers have applied NIR imaging in rat model of acute myocardial infarction (AMI), using

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1628-446: Is significantly cheaper than either PET or fMRI. However it lacks good spatial (i.e., where exactly the particle is) or temporal (i.e., did the contrast agent signal happen at this millisecond, or that millisecond) resolution. Additionally, due to the radioactivity of the contrast agent, there are safety aspects concerning the administration of radioisotopes to the subject, especially for serial studies. Positron emission tomography (PET)

1702-399: Is simply the exact opposite of respiration as it ultimately produces molecules of glucose. Cell signaling or cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly. Signaling can occur through direct cell contact or endocrine , paracrine , and autocrine signaling . Direct cell-cell contact is when a receptor on

1776-547: Is strongly linked to the cell mitochondrial channel's ongoing reconfiguration through a range of mechanisms known as mitochondrial membrane dynamics, including endomembrane fusion and fragmentation (separation) and ultrastructural membrane remodeling. As a result, mitochondrial dynamics regulate and frequently choreograph not only metabolic but also complicated cell signaling processes such as cell pluripotent stem cells, proliferation, maturation, aging, and mortality. Mutually, post-translational alterations of mitochondrial apparatus and

1850-713: Is the Pap smear , a screening test used to detect cervical cancer , and precancerous cervical lesions that may lead to cervical cancer. The cell cycle is composed of a number of well-ordered, consecutive stages that result in cellular division. The fact that cells do not begin the next stage until the last one is finished, is a significant element of cell cycle regulation. Cell cycle checkpoints are characteristics that constitute an excellent monitoring strategy for accurate cell cycle and divisions. Cdks, associated cyclin counterparts, protein kinases, and phosphatases regulate cell growth and division from one stage to another. The cell cycle

1924-514: Is the cell growth phase – makes up approximately 95% of the cycle. The proliferation of cells is instigated by progenitors. All cells start out in an identical form and can essentially become any type of cells. Cell signaling such as induction can influence nearby cells to determinate the type of cell it will become. Moreover, this allows cells of the same type to aggregate and form tissues, then organs, and ultimately systems. The G1, G2, and S phase (DNA replication, damage and repair) are considered to be

1998-414: Is vital for upholding the correct cellular balance. Autophagy instability leads to a variety of illness symptoms, including inflammation, biochemical disturbances, aging, and neurodegenerative, due to its involvement in controlling cell integrity. The modification of the autophagy-lysosomal networks is a typical hallmark of many neurological and muscular illnesses. As a result, autophagy has been identified as

2072-642: The International System of Units (SI). One tesla is equal to one weber per square metre . The unit was announced during the General Conference on Weights and Measures in 1960 and is named in honour of Serbian-American electrical and mechanical engineer Nikola Tesla , upon the proposal of the Slovenian electrical engineer France Avčin . A particle, carrying a charge of one coulomb (C), and moving perpendicularly through

2146-489: The germline depends on the effectiveness of processes for avoiding DNA damage and repairing those DNA damages that do occur. Sexual processes in eukaryotes , as well as in prokaryotes , provide an opportunity for effective repair of DNA damages in the germ line by homologous recombination . The cell cycle is a four-stage process that a cell goes through as it develops and divides. It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M). The cell either restarts

2220-538: The 1970s allowed mapping of the distribution of the radioisotopes in the organ or tissue, and led to the technique now called single photon emission computed tomography (SPECT). The imaging agent used in SPECT emits gamma rays, as opposed to the positron emitters (such as F ) used in PET. There are a range of radiotracers (such as Tc , In , I , Tl ) that can be used, depending on

2294-422: The DNA repair checkpoints The cell cycle is a sequence of activities in which cell organelles are duplicated and subsequently separated into daughter cells with precision. There are major events that happen during a cell cycle. The processes that happen in the cell cycle include cell development, replication and segregation of chromosomes.  The cell cycle checkpoints are surveillance systems that keep track of

Molecular imaging - Misplaced Pages Continue

2368-512: The OMM connects to other cellular organelles, such as the endoplasmic reticulum (ER), lysosomes, endosomes, and the plasma membrane. Mitochondria play a wide range of roles in cell biology, which is reflected in their morphological diversity. Ever since the beginning of the mitochondrial study, it has been well documented that mitochondria can have a variety of forms, with both their general and ultra-structural morphology varying greatly among cells, during

2442-441: The cell cycle's integrity, accuracy, and chronology. Each checkpoint serves as an alternative cell cycle endpoint, wherein the cell's parameters are examined and only when desirable characteristics are fulfilled does the cell cycle advance through the distinct steps. The cell cycle's goal is to precisely copy each organism's DNA and afterwards equally split the cell and its components between the two new cells. Four main stages occur in

2516-449: The cell cycle, and in response to metabolic or cellular cues. Mitochondria can exist as independent organelles or as part of larger systems; they can also be unequally distributed in the cytosol through regulated mitochondrial transport and placement to meet the cell's localized energy requirements. Mitochondrial dynamics refers to the adaptive and variable aspect of mitochondria, including their shape and subcellular distribution. Autophagy

2590-502: The cell genome. When erroneous nucleotides are incorporated during DNA replication, mutations can occur. The majority of DNA damage is fixed by removing the defective bases and then re-synthesizing the excised area. On the other hand, some DNA lesions can be mended by reversing the damage, which may be a more effective method of coping with common types of DNA damage. Only a few forms of DNA damage are mended in this fashion, including pyrimidine dimers caused by ultraviolet (UV) light changed by

2664-455: The cell has completed its growth process and if it is found to be damaged or altered, it undergoes cell death, either by apoptosis or necrosis , to eliminate the threat it can cause to the organism's survival. The ancestry of each present day cell presumably traces back, in an unbroken lineage for over 3 billion years to the origin of life . It is not actually cells that are immortal but multi-generational cell lineages. The immortality of

2738-457: The cell membrane, Golgi apparatus, endoplasmic reticulum, and mitochondria. With the conclusion of the autophagocyte, the phagophore's enlargement comes to an end. The auto-phagosome combines with the lysosomal vesicles to formulate an auto-lysosome that degrades the encapsulated substances, referred to as phagocytosis. Tesla (unit) The tesla (symbol: T ) is the unit of magnetic flux density (also called magnetic B-field strength) in

2812-588: The cell theory, adding that all cells come from the division of pre-existing cells. Viruses are not considered in cell biology – they lack the characteristics of a living cell and instead are studied in the microbiology subclass of virology . Cell biology research looks at different ways to culture and manipulate cells outside of a living body to further research in human anatomy and physiology , and to derive medications. The techniques by which cells are studied have evolved. Due to advancements in microscopy, techniques and technology have allowed scientists to hold

2886-457: The circulatory and renal systems while exhibiting long-term toxicity.. Several studies have demonstrated the use of infrared dye-labeled probes in optical imaging. It is important to note that addition of an NIR probe to any vector can alter the vector's biocompatibility and biodistribution. Therefore, it can not be unequivocally assumed that the conjugated vector will behave similarly to the native form. The development of computed tomography in

2960-420: The components of cells and how cells work is fundamental to all biological sciences while also being essential for research in biomedical fields such as cancer , and other diseases. Research in cell biology is interconnected to other fields such as genetics , molecular genetics , molecular biology , medical microbiology , immunology , and cytochemistry . Cells were first seen in 17th-century Europe with

3034-421: The cycle from G1 or leaves the cycle through G0 after completing the cycle. The cell can progress from G0 through terminal differentiation. Finally, the interphase refers to the phases of the cell cycle that occur between one mitosis and the next, and includes G1, S, and G2. Thus, the phases are: The scientific branch that studies and diagnoses diseases on the cellular level is called cytopathology . Cytopathology

Molecular imaging - Misplaced Pages Continue

3108-410: The density of positron annihilations in a specific area. When enough interactions and annihilations have occurred, the density of the original molecule may be measured in that area. Typical isotopes include C , N , O , F , Cu , Cu , I , Br , Rb , Zr and Ga , with F being the most clinically utilized. One of

3182-496: The derivation of the weber from volts (V), W b = V ⋅ s {\displaystyle \mathrm {Wb=V{\cdot }s} } : T = V ⋅ s m 2 . {\displaystyle \mathrm {T={\dfrac {V{\cdot }{s}}{m^{2}}}} .} The tesla is named after Nikola Tesla . As with every SI unit named for a person, its symbol starts with an upper case letter (T), but when written in full, it follows

3256-468: The description of the human genome. New paths in fundamental research, as well as in applied and industrial research, render the task of scientists more complex and increase the demands on them. Therefore, a tailor-made teaching program is in order. Molecular imaging differs from traditional imaging in that probes known as biomarkers are used to help image particular targets or pathways. Biomarkers interact chemically with their surroundings and in turn alter

3330-509: The development of transmembrane contact sites among mitochondria and other structures, which both have the potential to link signals from diverse routes that affect mitochondrial membrane dynamics substantially, Mitochondria are wrapped by two membranes: an inner mitochondrial membrane (IMM) and an outer mitochondrial membrane (OMM), each with a distinctive function and structure, which parallels their dual role as cellular powerhouses and signaling organelles. The inner mitochondrial membrane divides

3404-400: The diagnosis of diseases such as cancer, and neurological and cardiovascular diseases. This technique also contributes to improving the treatment of these disorders by optimizing the pre-clinical and clinical tests of new medication. They are also expected to have a major economic impact due to earlier and more precise diagnosis. Molecular and Functional Imaging has taken on a new direction since

3478-461: The eukaryotes. In G1, the cell is usually active and continues to grow rapidly, while in G2, the cell growth continues while protein molecules become ready for separation. These are not dormant times; they are when cells gain mass, integrate growth factor receptors, establish a replicated genome, and prepare for chromosome segregation. DNA replication is restricted to a separate Synthesis in eukaryotes, which

3552-429: The excitation source. Light is absorbed by endogenous chromophores found in living tissue (e.g. hemoglobin, melanin, and lipids). In general, light absorption and scattering decreases with increasing wavelength. Below ~700 nm (e.g. visible wavelengths), these effects result in shallow penetration depths of only a few millimeters. Thus, in the visible region of the spectrum, only superficial assessment of tissue features

3626-419: The fact that whether a static electromagnetic field is seen as purely magnetic, or purely electric, or some combination of these, is dependent upon one's reference frame (that is, one's velocity relative to the field). In ferromagnets , the movement creating the magnetic field is the electron spin (and to a lesser extent electron orbital angular momentum ). In a current-carrying wire ( electromagnets )

3700-457: The field. In this way, a European Master Programme "EMMI" is being set up to train a new generation of professionals in molecular imaging. Recently the term molecular imaging has been applied to a variety of microscopy and nanoscopy techniques including live-cell microscopy, Total Internal Reflection Fluorescence (TIRF)-microscopy, STimulated Emission Depletion (STED)-nanoscopy and Atomic Force Microscopy (AFM) as here images of molecules are

3774-435: The following molecular components: Cell metabolism is necessary for the production of energy for the cell and therefore its survival and includes many pathways and also sustaining the main cell organelles such as the nucleus, the mitochondria, the cell membrane etc. For cellular respiration , once glucose is available, glycolysis occurs within the cytosol of the cell to produce pyruvate. Pyruvate undergoes decarboxylation using

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3848-419: The fundamental units of life. The growth and development of cells are essential for the maintenance of the host and survival of the organism. For this process, the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication , cell division , regeneration, and cell death . The cell cycle is divided into four distinct phases : G1, S, G2, and M. The G phase – which

3922-418: The gamma camera around the patient, a three-dimensional image of the distribution of the radiotracer can be obtained by employing filtered back projection or other tomographic techniques. The radioisotopes used in SPECT have relatively long half lives (a few hours to a few days) making them easy to produce and relatively cheap. This represents the major advantage of SPECT as a molecular imaging technique, since it

3996-516: The image according to molecular changes occurring within the area of interest. This process is markedly different from previous methods of imaging which primarily imaged differences in qualities such as density or water content. This ability to image fine molecular changes opens up an incredible number of exciting possibilities for medical application, including early detection and treatment of disease and basic pharmaceutical development. Furthermore, molecular imaging allows for quantitative tests, imparting

4070-551: The imaging of gene expression and the development of novel biomarkers. Organizations such as the SNMMI Center for Molecular Imaging Innovation and Translation (CMIIT) have formed to support research in this field. In Europe, other "networks of excellence" such as DiMI (Diagnostics in Molecular Imaging) or EMIL (European Molecular Imaging Laboratories) work on this new science, integrating activities and research in

4144-538: The insertion of methyl or ethyl groups at the purine ring's O6 position. Mitochondria are commonly referred to as the cell's "powerhouses" because of their capacity to effectively produce ATP which is essential to maintain cellular homeostasis and metabolism. Moreover, researchers have gained a better knowledge of mitochondria's significance in cell biology because of the discovery of cell signaling pathways by mitochondria which are crucial platforms for cell function regulation such as apoptosis. Its physiological adaptability

4218-481: The interphase portion of the cycle, while the M phase ( mitosis ) is the cell division portion of the cycle. Mitosis is composed of many stages which include, prophase, metaphase, anaphase, telophase, and cytokinesis, respectively. The ultimate result of mitosis is the formation of two identical daughter cells. The cell cycle is regulated in cell cycle checkpoints , by a series of signaling factors and complexes such as cyclins, cyclin-dependent kinase , and p53 . When

4292-471: The invention of the compound microscope . In 1665, Robert Hooke referred to the building blocks of all living organisms as "cells" (published in Micrographia ) after looking at a piece of cork and observing a structure reminiscent of a monastic cell ; however, the cells were dead. They gave no indication to the actual overall components of a cell. A few years later, in 1674, Anton Van Leeuwenhoek

4366-449: The lysosomal membrane to enclose the cytosol or organelles. The chaperone-mediated autophagy (CMA) protein quality assurance by digesting oxidized and altered proteins under stressful circumstances and supplying amino acids through protein denaturation. Autophagy is the primary intrinsic degradative system for peptides, fats, carbohydrates, and other cellular structures. In both physiologic and stressful situations, this cellular progression

4440-489: The major disadvantages of PET is that most of the probes must be made with a cyclotron. Most of these probes also have a half life measured in hours, forcing the cyclotron to be on site. These factors can make PET prohibitively expensive. PET imaging does have many advantages though. First and foremost is its sensitivity: a typical PET scanner can detect between 10 mol/L to 10 mol/L concentrations. Cell biology Cell biology (also cellular biology or cytology )

4514-486: The mitochondrial lumen into two parts: the inner border membrane, which runs parallel to the OMM, and the cristae, which are deeply twisted, multinucleated invaginations that give room for surface area enlargement and house the mitochondrial respiration apparatus. The outer mitochondrial membrane, on the other hand, is soft and permeable. It, therefore, acts as a foundation for cell signaling pathways to congregate, be deciphered, and be transported into mitochondria. Furthermore,

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4588-402: The most prominent type, have several different shapes , although most are spherical or rod-shaped . Bacteria can be classed as either gram-positive or gram-negative depending on the cell wall composition. Gram-positive bacteria have a thicker peptidoglycan layer than gram-negative bacteria. Bacterial structural features include a flagellum that helps the cell to move, ribosomes for

4662-468: The multi-enzyme complex to form acetyl coA which can readily be used in the TCA cycle to produce NADH and FADH 2 . These products are involved in the electron transport chain to ultimately form a proton gradient across the inner mitochondrial membrane. This gradient can then drive the production of ATP and H 2 O during oxidative phosphorylation . Metabolism in plant cells includes photosynthesis which

4736-411: The readout. There are many different modalities that can be used for noninvasive molecular imaging. Each have their different strengths and weaknesses and some are more adept at imaging multiple targets than others. MRI has the advantages of having very high spatial resolution and is very adept at morphological imaging and functional imaging. MRI does have several disadvantages though. First, MRI has

4810-427: The rules for capitalisation of a common noun ; i.e., tesla becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case. In the production of the Lorentz force , the difference between electric fields and magnetic fields is that a force from a magnetic field on a charged particle is generally due to the charged particle's movement, while the force imparted by an electric field on

4884-518: The sensitivity of the contrast agents, these targeting moieties are usually linked to high payload MRI contrast agents or MRI contrast agents with high relaxivities. In particular, the recent development of micron-sized particles of iron oxide (MPIO) allowed to reach unprecedented levels of sensitivity to detect proteins expressed by arteries and veins. There are a number of approaches used for optical imaging. The various methods depend upon fluorescence , bioluminescence , absorption or reflectance as

4958-478: The smallest form of life. Prokaryotic cells include Bacteria and Archaea , and lack an enclosed cell nucleus.  Eukaryotic cells are found in plants, animals, fungi, and protists. They range from 10 to 100 μm in diameter, and their DNA is contained within a membrane-bound nucleus. Eukaryotes are organisms containing eukaryotic cells. The four eukaryotic kingdoms are Animalia, Plantae, Fungi, and Protista. They both reproduce through binary fission . Bacteria,

5032-416: The source of contrast. Optical imaging's most valuable attribute is that it and ultrasound do not have strong safety concerns like the other medical imaging modalities. The downside of optical imaging is the lack of penetration depth, especially when working at visible wavelengths. Depth of penetration is related to the absorption and scattering of light, which is primarily a function of the wavelength of

5106-426: The specific application. Xenon ( Xe ) gas is one such radiotracer. It has been shown to be valuable for diagnostic inhalation studies for the evaluation of pulmonary function; for imaging the lungs; and may also be used to assess rCBF. Detection of this gas occurs via a gamma camera —which is a scintillation detector consisting of a collimator, a NaI crystal, and a set of photomultiplier tubes. By rotating

5180-406: The study of cell metabolism , cell communication , cell cycle , biochemistry , and cell composition . The study of cells is performed using several microscopy techniques, cell culture , and cell fractionation . These have allowed for and are currently being used for discoveries and research pertaining to how cells function, ultimately giving insight into understanding larger organisms. Knowing

5254-430: The three basic types of autophagy. When macro autophagy is triggered, an exclusion membrane incorporates a section of the cytoplasm, generating the autophagosome, a distinctive double-membraned organelle. The autophagosome then joins the lysosome to create an autolysosome, with lysosomal enzymes degrading the components. In micro autophagy, the lysosome or vacuole engulfs a piece of the cytoplasm by invaginating or protruding

5328-434: The translation of RNA to protein, and a nucleoid that holds all the genetic material in a circular structure. There are many processes that occur in prokaryotic cells that allow them to survive. In prokaryotes, mRNA synthesis is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase. The prokaryotic polymerase consists of a core enzyme of four protein subunits and

5402-433: The various activities that cells and tissues perform in both health and disease. Molecular imaging emerged in the mid twentieth century as a discipline at the intersection of molecular biology and in vivo imaging. It enables the visualisation of the cellular function and the follow-up of the molecular process in living organisms without perturbing them. The multiple and numerous potentialities of this field are applicable to

5476-533: Was the first to analyze live cells in his examination of algae . Many years later, in 1831, Robert Brown discovered the nucleus . All of this preceded the cell theory which states that all living things are made up of cells and that cells are organisms' functional and structural units. This was ultimately concluded by plant scientist Matthias Schleiden and animal scientist Theodor Schwann in 1838, who viewed live cells in plant and animal tissue, respectively. 19 years later, Rudolf Virchow further contributed to

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