Magnetic Resonance Imaging Technology - Research Paper Example

? Magnetic Resonance Imaging Technology      Magnetic Resonance Imaging Technology Introduction Magnetic resonance imaging (MRI)technology is a type of medical imaging technique, which is applied in radiology-based visualization of internal anatomic structures and physiologic processes (U.S. FDA, 2012). The technology makes use of nuclear magnetic resonance (NMR) properties to image atom nuclei within the body. The human body is a “magnet” by virtue of the fact that it has ionic hydrogen that has a positive charge and a magnetic spin. However, this magnetic spin does not make humans magnetic because these protons spin in a haphazard manner, which cancels out the magnetic properties held by each ion (Hendee & Christopher, 1984). MRI technology harnesses this magnetic spin in ionic hydrogen within the body to develop MRI imaging by an MRI scanner. The MRI scanner is machine made of powerful and large magnets, which are used to align the atomic nuclei through magnetization. Thereafter, radio frequency fields are used to form the alignment of magnetized nuclei in a systematic manner. The application of radio frequency makes the nuclei develop magnetic fields that rotate and are detectable (Hendee & Christopher, 1984). The detected fields produce information, which is recorded and used in the development of the image of the scanned part of the body. The gradients of different magnetic fields make nuclei in different imaged locations to precess with differing speed, and this allows the recovery of spatial information through Fourier analysis of the detected signals. The use of gradients in differing directions allows the acquisition of 3D and 2D volumes in all arbitrary orientations (Hendee & Christopher, 1984). The ability of MRI imaging to offer good contrasting between tissues of different organs makes it an appropriate imaging technique for soft tissues in organs such as the heart and brain as well as muscles. MRI Working Mechanism MRI scanners rely on the magnetic properties of the ions in the body and their ability to align along strong magnetic fields to develop detectable signals that can be converted into images. The human tissues contain water, which has hydrogen nuclei, which can easily align according to the magnetic field of the scanner. The water molecules have two protons or hydrogen nuclei, and when a person is placed within the scanner’s magnetic field the magnetic moment of the nuclei align along the magnetic fields (Thulborn et al., 1982). During carrying out the scanning process radio frequency is used to produce a varying field of electromagnetism. The generated field of electromagnetism has frequency that is at a resonance frequency, which is absorbed and also causes a flip in the spin of the protons in the field of electromagnetism. After turning off the field of electromagnetism generated, the spins of nuclei that had aligned to the magnetic field return to their original thermodynamic equilibrium (Hendee & Christopher, 1984). In the process the bulk magnetization undergoes re-alignment with the static field of electromagnetism. In this process a radio frequency signal is developed, which is measurable by receiver coils. In order to acquire three-dimensional images additional magnetic fields are applied during scanning so as to learn the origin of particular signals in 3-dimensional space (Wu et al., 1999). The applied additional fields are used to generate signals that can be detected from specific parts of the scanned body. The spatial excitation helps in generating 3-dimensional images. The applied additional magnetic fields could also make the magnetization generated to precess at differing frequencies at particular scanned locations (Thulborn et al., 1982). This allows acquisition of k-space encoding that offers spatial information about the scanned part of the body. The 3-dimensional images acquired can be rotated in different orientations, and the manipulations can enable the detection of structural changes in the body. The different magnetic fields that are generated are a result of varying field strength, which occurs due to the current passing through gradient coils. The field strengths are different within the magnet depending on the spatial position of the scanned part within the magnetic field. Therefore, the radio signals generated and their frequency depends on the position of origin in a manner that is predictable. Inverse Fourier transform is applied in the recovery of the protons distribution within the body from the signal detected during scanning (Wu et al., 1999). The aligned protons within different body tissues reach their equilibrium at varying rates of relaxation. Tissue variables such as T2 and T1 relaxation times and spectral shifts as well as spin density could be used in the construction of images. The MRI scanner’s settings could be changed to develop contrast in images generated from scanned tissues depending on the properties of the tissues. The ability to develop such contrasts helps in the detection of injuries and abnormal tissue growths. In order to enhance differentiation of tissues and scanned parts of the anatomy other new technologies including intravenous injection of contrast agents in tissues has been employed (Hendee & Christopher, 1984). The agents injected into tissues or the vascular system enhances the appearance of tumors, blood vessels and areas of inflammation or injury in the developed images. Application of MRI In clinical set ups magnetic resonance imaging is applied in distinguishing pathologic tissues including tumors from normal human tissues. The MRI scanners offer better spatial resolution that can enable the distinguishing of two different structures at a very small distance. The high contrast resolution enables the determination of differences between two tissues that not be identical, but could be arbitrarily similar (Wu et al., 1999). Commonly diagnosed conditions that depend on MRI image analysis include: Joint injuries and abnormalities Evaluation of the vascular system for stenosis or aneurysm Cysts, tumours and any other internal abnormal growths Cardiovascular problems Pelvic pain problems among women, which include endometriosis and fibroids Liver diseases and other conditions affecting abdominal organs Brain problems Uterine abnormalities (U.S FDA, 2012). MRIs could also be used in studying the functions of the body. For example, MRIs have been used in the study of the brain. The MRIs are used to determine the parts of the brain and their functional roles in controlling various parts of the body. The study of functional role of the brain could also be used in determining portions of the brain affected by tumors or injury. Therefore, apart from clinical diagnosis, MRI is an important study tool, which is very helpful in studying the human anatomy and the functions of various body organs. This finds application in the generation of functional MRIs (fMRI’s), which help in determining changes in neural activity during various activities (Thulborn et al., 1982). MRI may also be used in measuring the levels of metabolites in the tissues. In such uses the use of this technology is referred to as ‘magnetic resonance spectroscopy’ (MRS). The magnetic resonance signal used generates a resonance spectrum, which corresponds to differing molecular arrangements of the ‘excited’ isotope. The signatures obtained are used in the diagnosis of specific metabolic disorders. The diagnosis method is common for metabolic disorders, which affect the brain (Higgins & Albert, 2006). Radiotherapy in cancer treatment requires that tumors should first be precisely located so as to direct the radiation appropriately without affecting adjacent tissues. MRI scanning is employed in the determination of the precise location, orientation and shape of tumors. The locating process is followed by tattooing, and thereafter appropriate triangulation of radiotherapy is conducted (Higgins & Albert, 2006). Interventional MRI is also a popular use of MRI, which yields images that are used to guide surgical processes so as to obtain minimally invasive process. There are developed technologies that allow concurrent imaging and surgery. The use of MRI enhances precision of the surgical process and ensures the surgical procedures performed are least invasive (Higgins & Albert, 2006). Real-time MRI is also being used in monitoring moving objects within the human systems by conducting continuous “filming.” The use of real-time MRI offers a promising future in studying and diagnosing cardiovascular problems as well as joint problems because real-time MRI allows the imaging of organs even when in function or motion (Stanford University, n.d). Magnetic resonance angiography is also another form of MRI used in imaging the vascular system for analysis of possible arterial problems such as stenosis or aneurysm. MRI versus other Imaging Methods such as Computed Tomography MRI differs significantly from other forms of imaging such as X-rays and computed tomography (CT). The uniqueness of MRI technology makes it better for some clinical uses than other forms of imaging. MRI uses radio frequencies that are non-ionizing to generate images of various body organs. As such, it is suited for imaging of soft body tissues. On the other hand, computed tomography uses x-rays, which are a form of ionizing radiation in the acquisition of images. The use of CT is preferred in the acquisition of images of body tissue that have a higher atomic number when compared to the tissue that surrounds them. The CT scanners pose a potential threat of DNA damage and cell ionization that could potentially lead to the development of cancer. According to Hall and Brenner (2007), an estimated 0.4% of cases of cancer in the United States could be attributed to past CT scanning. In spite of the fact that CT scanning does not pose an ionizing threat, it also has its own potential challenges. The development of imaging contrast in MRI is acquired through the use of various methods such as the change of scanning parameters or tissue contrast enhancement through the use of contrast agents that show the features of imaged areas with more clarity. On the other hand, CT scanning employs x-ray attenuation and contrast agents as the only ways to generate contrast in images done by CT scanning. However, contrast agents used in Ct scanning are different from those used in MRI scanning. The CT scanning contrast agents contain a higher atomic number (Wu et al., 1999). The number should be higher than the atomic number of the surrounding tissue so as to facilitate the contrast required. Examples of contrast agents used in CT scanning include barium and iodine. On the other hand, contrast agents used in MRI scanning are compounds with paramagnetic properties. Examples of contrast agents used in MRI scanning include manganese and gadolinium. These agents aid in altering tissue relaxation times. The use of contrast agents in both imaging processes is contraindicated for patients with kidney problems because they may aggravate their condition. MRI scanning has the potential to develop cross-sectional images in all planes. CT scanners were in the past limited to only acquiring images on an axial plane. However, with development of multi-detector computed tomography scanners that have an ability to retrospectively reconstruct data in all planes the CT scanners can also achieve scanning ability in all dimensions. However, the detection of brain tumors is best supported by MRI scanners, which are generally superior when compared with CT scanners (Allen et al., 1993). On the other hand, CT scanners offer the best diagnosis of tumors in the chest and brain because it has fewer problems from motion artifact when compared to MRI scanners. In addition, CT scanners are often used because they are more affordable and easily available than MRI. However, there is a risk of being exposed to ionizing radiation. In cases where patients have to undergo successive scanning MRI scanning is preferable because it leads to little exposure to ionizing radiation. CT scans could be used in varied conditions and cases, but MRI can only be used on patients without any type of implant such as insulin pumps, defibrillators, loop recorders, brain stimulators, cochlear implants, vagus nerve stimulators and any other foreign bodily implants such as prostheses. The presence of such foreign bodies within the scanned areas during the scanning process could result in overheating or malfunction. Therefore, patients with such implants should consider other options. Economics of MRI is healthcare In the past 3.0 tesla magnetic resonance machines cost an estimated $2 to $ 2.3 million dollars, whereas; 1.5 tesla magnetic resonance imaging machines cost an estimated $1million to $1.5 million dollars (Stanford University, n.d). In spite of these high acquisition costs MRI scanners contribute to significant earnings by healthcare service providers. This is because they earn a significant amount of revenue in terms of reimbursement, which is often at favorable rates offered by the insurers and Federal government. The reimbursements from insurers come in form of two components which include a professional charge for the radiologist review as well as an equipment charge for the MRI scan. The rates for interpretation and equipment owner are not significant, and they mainly depend on negotiations between parties and the insurance companies. The rates may also be determined by the Medicare schedule. However, it has to be noted that there is a need for pre-approval of the MRI scan presented to the insurance companies before they can ratify the reimbursement. The “Deficit Reduction Act” from 2005 led to significant reduction of reimbursement fees paid by both the Federal programs and insurance firms (Stanford University, n.d). Advantages of MRI  Magnetic resonance imaging presents a high comparative resolution and helps in differentiating two tissues that may seem similar, but not identical. The differentiation of tissues offered by MRIs is important because it allows discrimination and characterization of different tissues by being able to differentiate their biochemical and physical characteristics (Wu et al., 1999). MRI also allows identification and differentiation of tissues that surround the skeletal framework such as the spine and posterior fossa. This is possible because calcium emits minimal signal on MR images. MRI is significantly advantageous than other scanning methods because it produces sectional images in any form of projection and orientation without moving the patient and thus offering greater convenience. The ability to perform scans in different planes enhance diagnostic utility and versatility, and thus creating significant advantage in planning of surgical and radiation treatments (National Heart, Lung and Blood Institute, 2012).   MRI technology does not use any form of radiation that is ionizing in nature, and therefore, patients are not exposed to any radiation risk. This is significantly beneficial for patients that have conditions, which may call for regular scanning, which could increase their risk getting cancer (National Heart, Lung and Blood Institute, 2012).   MRI scanning is programmable for further acquisition of information beyond structural and compositional differences. There are other physiological phenomena such as velocity of moving body fluids that are detectable through programming that can enable encoding of such information. This information obtainable during MRI scans could help in detecting problems such as stroke (National Heart, Lung and Blood Institute, 2012).     MRI has a higher level of acceptability among patients as a diagnostic tool because it is less invasive in nature and require minimal to no preparation from the patients before they are scanned (National Heart, Lung and Blood Institute, 2012).   Contrast agents used in MRI are tolerable and have limited potential to cause allergies or impair functions of the kidney. This makes the use of MRI advantageous and more acceptable among the patients because there is little fear of possible complications resulting from the use of contrast agents (National Heart, Lung and Blood Institute, 2012).   MRIs are also very important from a cardiac perspective because they can perform several and diverse diagnostic functions. The functions may include cardiac anatomy imaging, stress and rest myocardial perfusion imaging-just to mention, but a few. All these imaging processes can be performed within a period of less than one hour (Manning & Dudley, 2010). In terms of vascular health MRI could carry out flow patterns assessment in the vascular system, carry out non-contrast enhanced angiograms and contrast enhanced angiograms (Manning & Dudley, 2010). The technology would also be applied in the characterization of vessel wall atheroma. In a congenital heart condition view, magnetic resonance imaging can evaluate and quantify inter-cardiac shunts, regurgitant lesions. It can also offer a comprehensive view of the vascular system, which facilitates better and easier diagnosis of the vascular health system. The imaging technology is, therefore, important for the whole cardiac and vascular system (Manning & Dudley, 2010). Limitations of MRI Acoustic noise is a significant problem in MRI scanning because the switching of field gradients results in a change of the Lorentz force, which occurs in the gradient coils. The changes cause minor contractions and expansions in the coils. The switching is always in within the audible frequency limits and the resultant vibration always causes loud noise in form of beeps and clicks, which could often be irritating for the patients under scanning (Higgins & Albert, 2006). The problem is often significant in high-field machines. The noise problem therefore elicits the consideration of ear protection to prevent discomfort during scanning. Claustrophobia is also a problem for patients that do not feel comfortable being locked up in closed spaces or enclosures. The challenge may, however, be overcome with a little counseling on the essence to go through the process (National Heart, Lung and Blood Institute, 2012).   MRI technology is not applicable in cases involving patients with implants of a medical nature such as pacemakers, insulin pumps and prostheses. These foreign bodies could possibly heat up or malfunction during the scanning process. As such, patients having these implants cannot get the benefit of MRI. Patients with acute illness or patients in a vegetative state cannot fully cooperate with the medical practitioners during the scanning process because of their conditions and this could possibly cause movement artifacts (Higgins & Albert, 2006). The examination of some obese patients is at times challenging or impossible because some MRI scanners have bore limits that cannot fit their body size. Therefore, extremely obese patients may be unable to get an MRI. However, this is not possible in methods of imaging such as CT scanning (Higgins & Albert, 2006). MRI scanning units need specialized housing within medical facilities. Additionally, these units require shielding, which prevents radio frequency interference. In addition to the housing and shielding needs, the MRI units are expensive to operate, maintain and purchase. As such, the units have a high initial set up cost that makes them costly. However, in spite of this disadvantage, the MRI scanners offer substantial savings in terms of medical expenses and diagnosis. Additionally, there is a need for greater technological expertise needed in handling MRI scanners when compared to other forms of imaging, and this adds to the costs of MRI (Shaleen, 2010). The patient throughput from MRI scanning is slow compared to other forms of imaging. Therefore, there is a higher time requirement for imaging when MRI technology is used instead of other clinical imaging methods. Conclusion and Recommendations MRI scanning has changed the medical imaging field significantly because of the new possibilities that it has enhanced in diagnosis and medical studies. The technology has made comparative resolution possible and improved imaging from multiple perspectives, thus allowing better medical imaging and the ability to diagnose a variety of conditions. The technology is safer when compared to other forms of imaging, which make use of ionizing radiation. The use of ionizing radiation increases the possibility of acquiring cancer, which is a leading problem currently in the United States. In addition to the beneficial capabilities of MRI in imaging, other programmable additions can be made so as to facilitate acquisition of more information than just images. MRI scanning is programmable for further acquisition of information beyond structural and compositional differences. There are other physiological phenomena such as velocity of moving body fluids that are detectable through programming that can enable encoding of such information. This information obtainable during MRI scans could help in detecting problems such as stroke. The acquisition of such information makes imaging by MRI more important because it facilitates the acquisition of more information than just imaging. In addition to this advantage, MRI is more acceptable among most patients and therefore, presents few challenges when convincing patients to undergo an MRI scan. In spite of the numerous advantages, there are a few disadvantages of MRI and these include the fact that it does not find applicability among patients with medical implants which include defibrillators and insulin pumps as well as prostheses. However, currently there are technologies under development, which may allow some patients to be scanned even with their implants still intact (Kumar & Jost, 1998). MRI patient throughput is also slow and the method may not be applicable for extremely obese patients as well as claustrophobic people. However, for people with claustrophobia a little counseling on how to overcome the fear may be necessary. In a nutshell, MRI imaging presents more advantages in clinical use than other forms of imaging and in spite of the few disadvantages the technology finds wider applicability and acceptance both for patients and practitioners. As such, it would be recommendable for most health facilities to consider acquiring MRI as their first imaging facility or equipment. This is important because even current imaging challenges in MRI have possible and promising research studies underway, which could improve the success of the method in future (Shaleen, 2010). References Hall, E. J. & Brenner, D. J. (2007). Computed tomography: An increasing source of radiation exposure. New England Journal of Medicine, 357 (22), 2277-84. Hendee, R. W. & Christopher, J. M. (1984). Magnetic Resonance Imaging Part I—Physical Principles. The Western Journal Medicine, 141 (4), 491–500 Higgins, B. C. & Albert, R. (2006). 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