Magnetic resonance imaging uses magnetic force to check whether the structures of the body are functioning well. Radio technology is also used in this process. The results are shown through a computer. The force from a magnet is used to hold the protons in their rightful place. Radio waves are then used to produce weak signals that the receiver detects from the MRI scanner as noted by Bhattacharys et al (2002). Magnetic resonance imaging is applied when accurate detection of disease in the body is required. Allain et al (1991, p.73-8) highlight some of the areas where MRI is applied. These include: scanning the brain, stroke, aneurysms, detection of spinal cord problems, and trauma. Also, accurate information is obtained when MRI is used to scan soft tissues, bones, and joints.
According to World Health Organization (2008, P.140-151), Parkinson’s disease falls under motor system disorders. Brain cells that are responsible for the manufacturing of dopamine are affected when one suffers from this disease. Parkinson’s disease can be identified through several symptoms. They include: taking long when one is walking from one place to another, losing one’s balance, inability to move one’s limbs, and general lack of coordination among various body organs. Some of these symptoms have been discussed by Berg, Godau & Walter (2008, p.1044-55). Parkinson’s disease (PD) occurs gradually, although in some people the progress is very fast. Chen, Seidel & Mertins (2010) revealed this progress in their research. Other symptoms that can be observed in relation to PD are skin problems, difficulty in swallowing and in speech, and urinary problems (Grisoli, Fetoni & Savoiardo 1995). In diagnosis of Parkinson’s disease, neurologists mainly depend on examination of the brain and the medical history of the patient. In their edition, Mehnert et al (2010) gave the effects of PD. This disease can result in disability thus affecting the daily activities of those suffering from PD.
MRI has been instrumental in assisting neurologists to identify the major cause of PD (Geng, Li & Zee 2006). The use of MRI in PD diagnosis proved effective in research findings recorded in various journals.
Parkinson’s disease is the second most common neurodegenerative disorder, which is caused by the impairment of nerve cells that are found in the brain area. This disease prevents substantia nigra from producing dopamine. Parkinson Study Group (1997, p.125-30) gives the chemical composition of dopamine and its functions. Dopamine is a chemical that facilitates the relay of messages from the substantia nigra to corpus striatum. If dopamine is not produced, this affects the performance of other nerves and the movement of the body (Freed et al 2001, p.710-9). The actual causes of Parkinson’s disease are not known, but there are some scholars who believe that this disorder can be caused by environmental factors, genetic factors and age. However, scientific evidence has not been given to support these beliefs.
PD affects about 5 million people in the world. Those above the age of 60 are the most affected. About 1% of people aged over 60 years, and 4% of those aged 80 years and above are likely to suffer from this disorder (Medinet 2012).
Evaluation of MRI in diagnosing PD
In order to evaluate MRI in the diagnosis of Parkinson’s disease, several alternative scan methods are discussed. Their strengths and shortfalls are analyzed against those of MRI.
First, it is imperative to note that neither the lab test nor clinical analysis can help in identifying the root cause of Parkinson’s disease. Typically, PD is diagnosed using a series of symptoms, the history of a particular patient and some clinical examinations. Doctors try a number of antiparkinsonian drugs, such as levodopa, when they discover the likelihood of PD (Tolcapone Study Group 1999, p.38-44). The administration of drugs minimizes the chances of the wrong diagnosis. However, these drugs have some side effects such as anxiety, nervousness, psychosis, sexual dysfunction, and nausea (Myllyla et al 1997, p.333-41).
If the symptoms persist after the prescription of drugs like levodopa, Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) is applied to help rule out other diseases that are likely to produce symptoms similar to those of Parkinson’s disease (Kier et al 2007, p.83-85).
Besides MRI, Computed tomography (CT), Positron emission tomography (PET), Single-photon emission tomography (SPECT), Generic test and Electroencephalograms (EEGs) are used in detecting Parkinson’s disease (Vignon et al 2009, p.2336-2339).
Computed tomography takes a clear structure of the body, where it eliminates all the overlapping parts. The x-ray tube is rotated around the patient and the images obtained are stored in a computer (Hutchinson & Raff 2000). The images are viewed from different angles for analysis. The image clearly shows the physicians and radiologists whether there is any abnormality, the details of that abnormality, and the specific location. In addition to clear images, CT minimizes the risks of radio waves (Strada 1994). CT guides in treatment of cardiac diseases, stroke, and brain disorders (Brennesis, Seppi & Schocke 2003). The doctor is able to decide if surgery is necessary. CT has shortfalls related to its application. These include allergic reactions due to “contrast material” and misinterpretation of minor abnormalities (Cordato, Pantelis & Hilliday 2002.). Also, a patient can be harmed by the radiation if exposed to them several times.
Another method that should be considered when discussing MRI is the PET scan. PET scan has a capacity to detect abnormalities in growing cells as well as give the functions of these cells (Watanabe, Fukatsu & Katsuno 2004). The analysis of this technique by Davie et al (1997) shows that this scanning method can help neurologists in detecting brain abnormalities like dementia, epilepsy, and Alzheimer’s. The unavailability of this scan and its adverse effects on pregnant women renders this method less applicable (Schneider et al 1995, p.1149-54).
Evaluation of MRI can be done through evaluation of Single-photon emission tomography (SPECT) (Ghaemi, Hilker & Rudolf 2002). This scan is only used in confirming diagnosis after a patient has gone through clinical examination. SPECT is not suitable in PD diagnosis because it cannot differentiate PD from Progressive Supranuclear Palsy (PSP) and Multiple System Atrophy (MSA) (Solveri et al 1999).
Other methods which can help in evaluating MRI are Generic tests and Electroencephalograms (EEGs) (Specht, Minnerop & Muller-Hubenthal 2005). Generic test involves testing three genes which are Parkin, Pink-1, and LRRK2 to diagnose PD (O’Neil, Schuff & Marks 2002). On the other hand, EEGs involve measuring and recording the electrical activity of the brain. The electroencephalograms can be used to diagnose narcolepsy, find out whether the brain of a person who is in a coma is dead, and in finding out the mental health status of a patient (Cordato, Duggins & Halliday 2005). The procedure used in EGG causes no pain and it is effective in displaying metabolic state of the cortical structures (Sibon & Tison 2004). On the contrary, this method makes the patient uncomfortable when the electrodes are placed on the scalp.
Evaluation of MRI entails putting into consideration the effectiveness, cost analysis and results of the person being diagnosed. MRI is very effective in the identification of very minute changes that may occur in various parts of the body that can be affected by this disease (Antonini & Ferrarini 2005). This scan is very important in offering the right diagnosis on the affected body parts (Levin et al 1991, p.412-6). The scanning technique is preferred by most surgeons because it is able to diagnose correctly (Kwon et al 2006, p.347-52). Variation in water content in different parts of the body and different magnetic properties that the body parts have enables the MRI to produce an image that can be clearly distinguished. The application of magnetism helps in the clear identification of internal abnormalities (Price et al 2004). MRI is preferred to standard x-ray and computed tomography because it displays details of cartilages and ligaments. MRI does not use high-energy radiations and this makes temporary exposure to the scanner less harmful as was proven by Vignon et al (2005, p.973-976).
Some of the shortcomings of MRI need to be highlighted for precaution purposes. To start with, the use of MRI can deter the functioning of metallic objects implanted on the body (Yue 1997, P. 355 – 371). Precaution should also be taken when using MRI by ensuring that no metallic materials hang loose so that they are not attracted. Skin burns may also be experienced on medical patches while prolonged exposure to radiations can cause body warming (Jarquin-Valdivia et al 2004, p.139-142). Acquainting the patient with radiology information and products that emit FDA’s radiations can help in preventing some of the adverse effects that result from MRI. As proposed by Aubry et al (2000, p.1623-1627), ultrasound brain scan can help reduce some of the side effects.
In early stages, it is difficult to diagnose Parkinson’s disease. One of the symptoms that may be experienced is resting tremor (Schrag, Kingsley &Phatouros 1998). Other symptoms include: rigidity and stiffness of limbs or full-body, Bradykinesia, taking longer to do something you used to do with a very short time, postural instability (having trouble instability when walking and stumbling very often), generalized fatigue, fatigue which even last for weeks despite having enough sleep, gastrointestinal problems, slurred speech, anosmia, depression, executive dysfunction and sleep disturbances (Ashburner & Friston 2000). It is very difficult to rule out from the above symptoms that one has Parkinson’s disease. Some people who are diagnosed with Parkinson’s never develop these signs. People who have been diagnosed with PD have been found with these symptoms. PD symptoms are highly variable from patient to patient (Savoiardo, Strada & Girotti 1990). Therefore, evaluation should be individualized.
Magnetic resonance imaging is a method used in diagnosing PD (Schulz, Skaleji & Wedekind 2004). It is a relatively easy and safe technique, proven to diagnose neurologic disorders (Brenneis, Seppi & Schocke 2004). The value of structural MRI is limited in the diagnosis of Parkinson’s disease as there is no specific structural change that has been found (Basser 1995). Patients with PD usually don’t have normal structural MRI (Specht, Minnerop & Abele 2003). PD is associated with an increased incidence of brain atrophy, which is usually frontally or generally predominant (Bonneville & Melter 2005). The pattern of atrophy in the brain is not specific enough to distinguish PD from other neurologic degenerative disorders (Savoiardo et al 1994 p. 93). The importance of structure MRI in differentiating PD from other parkinsonian disorders like progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), multiple system atrophy (MSA) and Parkinsonism.
Predominant automatic dysfunction (MSA-A) and predominant Parkinsonism (MSA-C) have their pathologic substrate found in the spinal cord (Bhattacharys et al 2002 p. 104). MRI does not detect changes in the intermediolateral columns of the spinal cord (Barone, Bravi & Bermejo-Pareja 1999, p.573-9). Clinical method does not differentiate between MSA-P and PD. MRI has the potential of helpful differential diagnosis of MSA-P (Schrag, Good & Miszkiel 2000). There are diagnostic algorithms based on MRI that have been proposed to help distinguish MSA-P patients from PD patients (Schrag, Kingsley & Phatourous 2000, p. 65). However, some patients fulfilling diagnostic criteria for clinically probable MSA-P had normal findings with these routine MRI methods. MRI modified method differentiate MSA and PD, as with T2 weighted MRI, in which hypointense putaminal signal changes are more often observed in MSA than in PD (Kraft & Trenkwalder 2002, p. 1265). Using thin slices substantially increases MR sensitivity in detecting abnormal putaminal T2 hypointensity in MSA patients (Righini et al 2002, p. 266). The sensitivity and specificity of MRI findings of MSA-C are high (Righini et al 2002, p. 266). Therefore, the combination of clinical features and MRI results makes the differential diagnosis of PD from MSA-C easy.
In, progressive supranuclear palsy (PSP), typical findings on MRI is atrophy found in the midbrain, which is accompanied by an enlarged cerebral aqueduct and perimesesencephalic cistern. According to Warmuth-Metz et al (2001, p.1076), the anteroposterior diameter of the Midbrain measured on axial T2- weighted MRI in PSD patients is significantly lower than that in PD patients. This difference is helpful in distinguishing PD from PSP. The “eye of the tiger” sign on brain MRI appears as bilaterally symmetric hyperintense signal changes in the interior medial globus pallidus on T2-weighted images and is typically associated with Hallervorden-Spartz disease (Davie et al 1997, p. 767). According to Oba et al (2005, p. 2050), people suffering from PSP have a smaller midbrain compared to people suffering from disorders such as MSA-P. This could be used to differentiate PSP patients from MSA-P patients. The area of the midbrain on midsagittal MRI is helpful in differentiating PSP from PD and MSA-P. Also, abnormal superior midbrain profile (flat or concave aspect) is helpful in the distinction of PSP from PD (Righini et al 2004, p. 927).
MRI plays an important role in the differential diagnosis of PD secondary to other structural brain lesions, such as brain tumor, multiple sclerosis, normal pressure or obstructive hydrocephalus, multiple infarcts, and subdural hematoma (Manyan et al 1992, p. 327). Improved MRI techniques in recent times’ substantia nigra have been identified using special methods. Sibon & Tison (2004, p. 49) developed a technique that uses two distinct inversion-recovery pulse sequences. The technique is used to calculate the ratio of the image acquired in the two sequences. By dividing the signal intensity of the white matter suppressed sequence, an image is obtained that clearly demonstrates the gray matter of the substantia nigra (Abe et al 2000). There is a loss of signal in a lateral-to-medial gradient in PD, even in early cases (Adachi et al 1999, p 1500). This is not demonstrated by routine MRI methods (Warmuth-Metz et al 2001, p.1076). A semi-automated segmentation analysis (SIRRIM) has been developed instead. SIRRIM segmentation analysis allows the substantia nigra to be displayed as an isolated structure. Areas of highest signal are thinned in PD patients compared to normal controls. In addition, the substantia nigra is broadened in a ventrodorsal direction in PD compared with normal controls (Summerfield, Junque & Tolosa 2005). Structural changes within the substantia nigra in PD are detected by using inversion-recovery MRI which correlates with the striatal dopaminergic function measured by (18)F-dopa positron emission tomography (PET) (Hurchison & Raff 2001, p.1194). These studies point to the possibility, with the refinement of this technique, of detecting early or even presymptomatic PD.
Other methods are not as effective as MRI. One of these is Magnetic Resonance Imaging-Based Volumetry (MRV). When using this method with automated segmentation techniques, volume loss of the brain can be detected. Studies using region of interest (ROI) – based MRV did not find any difference between PD patients and controls (Solveri et al 1999, p.204). Changes in several structures have been reported, such as a decrease in striatal and brainstem volumes in MSA and PSP patients (Testa, Savoiardo & Fetoni 1993). In contrast to these MRV studies, the use of VBM method did reveal grey matter loss in PD patients. In PD with dementia, reduced gray matter volume compared to controls has been shown in extensive brain regions, including the temporal lobe, occipital lobe, hippocampus, frontal lobe and left parietal lobe, thalamus, caudate nucleus, bilateral putamen, and accumbens nuclei (Savoiardo et al 1989, p. 555). PD patients without dementia have reduced grey matter volume in the frontal lobe, limbic/paralimbic areas, hippocampus, left anterior cingulate gyrus, caudate nucleus, and left superior temporal gyrus (Soliveri, Monza & Paridi 2000). VBM studies have investigated volume loss in Parkinsonian patients and compared the results with PD. There is extensive cortical and subcortical volume loss in MSA-P patients compared with PD patients.
Diffusion-weighted imaging is another method that is used to detect PD. This method has the potential of differentiating PD from other parkinsonian syndromes. According to Schockle et al (2002 p. 575), MSA-P patients have higher putaminal regional ADC than PD patients.
Magnetization Transfer Imaging is another method, based on the interactions between highly bound protons within structures such as myelin or cell membranes. They are very mobile protons of free water. MTI, in investigation of PD, showed no differences in MTRs in any region between non-demented PD patients and controls. However, PD patients with dementia had significantly lower MTRs in the subcortical Hurchison & Raff (2001, p. 300)
Generic test is another method. Significant advancement has been achieved in finding generic causes for PD. Several genes have been identified. However, these genes are rare and many of those diagnosed with PD do not carry any of the genes. Only three genes can be tested commercially. They are Parkin, Pink-1, and LRRK2. Information from these tests does not alter treatment being undertaken. Consequently, we cannot rely on generic tests to diagnose PD. The generic test is very expensive.
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