Brain Imaging Modalities



Comparison of MRI and CT As Brain Imaging Modalities

By

Reda El Mkhantar

108855467

BME 300

Professor Congwu Du

Abstract

Functional imaging is the study of human brain function using brain imaging modalities such as magnetic resonance imaging (MRI) and computed tomography (CT). The aim is to examine and then compare these two modalities in different neural applications. MRI and CT were examined in the identification of bacterial and parasitic infections. Each modality was used to detect a wide range of infectious diseases among which bacterial meningitis, infectious myelitis and neurocysticercosis (Raibagkar et al. 2014). MRI was then examined in its use for insights into suicidal behavior where MRI was used to detect white matter hyper intensities among young adults who exhibited suicidal behavior (Ehrlich et al. 2005). Finally, MRI and CT were examined and compared in their identification and quantification of intraventricular hemorrhage in the brain to determine which neuroimaging modality is superior (Romanova et al. 2014)..

For neurological infections MRI was found to be a much superior modality for imaging most infections unless the infection caused calcification in which case CT was more specific [1]. For white matter study and its relation to suicide, MRI was used for psychological purposes [2]. MRI has a much higher contrast than CT which allows it to discriminate between grey and white matter in the brain to identify patterns that may help in suicide detection and prevention [2]. For intraventricular hemorrhage detection and quantification, MRI was more sensitive than CT which failed to diagnose the condition in 3% of the cases [3]. MRI had 100% sensitivity [3]. CT Had lower Graeb scores than MRI which means that CT was less specific than MRI [3]. This was superior for the diagnostic of intraventricluar hemorrhage [3]. The use and development of neuroimaging modalities is crucial and can help significantly reduce fatalities from serious conditions. In these three examples of neuroimaging applications, MRI was shown to be consistently superior to CT imaging.

Introduction

MRI and CT both have their advantages and disadvantages and are designed for specific diagnostics. CT is much cheaper than MRI and is usually sufficient to image many neurological disorders [1]. CT is less sensitive to movement of the patient compared to MRI and can be preformed more rapidly. CT can be performed on patients with metal devices in their body such as an implantable pacemaker. On the other hand, MRI does not use ionizing radiation and can be preferred over CT. MRI also shows much greater soft tissue contrast, and is more sensitive and specific to changes within the brain.

Neurological infections, are responsible for significant global mortality [1]. MRI and CT allow for the diagnosis of nervous system infections [1]. Both CT and MRI can be used to image and detect particular features of several bacterial and parasitic nervous system infections [1]. MRI can also be used to examine the neural factors associated with suicide related behaviors [2]. Magnetic resonance imaging is used to image and distinguish gray matter and white matter hyper intensities which may be associated to suicidal behavior [2]. MRI and CT also are effective at imaging hemorrhages in the brain [3].

Magnetic resonance imaging (MRI) and computed tomography (CT) allow for the study of the brain noninvasively to examine abnormal brain activity. In this paper the goal is to compare and answer the question of which imaging modality is better for imaging the brain. The answer depends on the purpose of the imaging, the part of the brain to be imaged and the type of neurological activity or disease among other considerations. In this paper we will investigate the use of MRI and CT for these different factors. We will examine the imaging of the white matter and grey matter and their association with suicide [2], the imaging of neurological infections especially bacterial and parasitical infections [1], and the imaging of intraventricular hemorrhage in the brain [3].

Methods and results

Neurological infections, bacterial and parasitic, are responsible for significant global mortality [1] . Neuroimaging with MRI and CT allows for diagnosis of nervous system infections [1]. In this research, both CT and MRI were used with the goal to image and detect particular features of several bacterial and parasitic nervous system infections [1]. The two modalities can detect different diseases with different accuracy and specificity [1]. For neurological infections, MRI can detect areas with abnormal blood flow volume and can show necrosis and pus [1]. The interruption of the blood brain barrier caused by infections can cause enhancement on the T1 weighted contrast image which allows for the detection infections such as cerebritis and meningitis [1]. With weighted contrast it is possible to image meningeal inflammations by distinguishing between the hyper intense signal due to inflammation and the weaker signal [1]. Also the restriction of the movement of water molecules as a result of infections such as cytotoxic edema can be detected by diffusion weighted imaging on MRI because it modifies the water diffusivity in the affected area [1]. These methods among others were used to distinguish between different neurological infections. Both CT and MRI were used for each type of neurological infection. The findings were recorded and the imaging modality of choice for each infection was then determined [1].

For Neurocysticercosis, the modality of choice was CT. Using CT, multiple cerebrospinal fluid cysts, hypodense cystic fluid with rim enhancement, peripheral edema and small calcified nodules were detected [1]. CT was especially important for the detection of the calcified nodules at the calcified stage although MRI was better at detecting rim enhancing cerebrospinal fluid cyst using T1 weighted and T2 weighted images [1]. For most of the other infectious diseases imaged such as bacterial meningitis and infectious myelitis, MRI is the modality of choice [1].

Structural MRI is the most widely used method in suicide research [2]. The most commonly studied diagnoses are major depressive disorder, bipolar disorder, and schizophrenia among others [2]. MRI among other neuroimaging modalities was used to examine the neural factors associated with suicide related behaviors [2]. Magnetic resonance imaging is used to image and distinguish gray matter and white matter hyper intensities which appear as bright signals on the T2-weighted MRI images [2]. Using structural MRI, variations in water content in different parts of the brain provide contrast, which allows for the differentiation between the gray matter and the white matter [2].

To identify patients at risk of suicide, a study was done to detect and compare the location and extent of white matter hyper intensities in patients with major depressive disorder using MRI [2]. The goal was to study white matter hyper intensities and their association with suicide using MRI [2].

In the study, 102 patients with major depressive disorder had their brained imaged for the presence of white matter hyper intensities using T2 weighted MRI images [2]. The history of suicide attempt was considered in the results section in addition to the images [2]. Fisher's Exact Tests was the used to determine whether there exists any correlation between white matter hyper intensities and suicidal behaviors [2]. The results showed that white matter hyper intensities were significantly higher in subjects who had a history of suicide attempts [2].

Both MRI and CT are effective at imaging hemorrhages in the brain [3]. The aim of this study was to compare the sensitivity of  MRI and CT in the detection and quantification of intraventricular hemorrhage [3].

In the experiment, there were 289 subjects of which 171 had intraventricular hemorrhage [3]. The patients with primary intraventricular hemorrhage had their brain imaged to detect the intraventricular hemorrhage then quantify the neuroimaging results using the Graeb score [3]. There were 68 MRI and 68 CT machines and the subjects with the condition were imaged in both machines in pairs [3]. The CT machines were 16 or 64 slice Siemens scanners and the MRI machines were 1.5T Siemens MR scanners. The MRI images were obtained using unenhanced sagittal and axial TI weighted images, T2 weighted turbo spin echo and axial diffusion weighted imaging [3]. The images were then given a Graeb score and the scores were compared with the Wilcoxon test for significance testing [3]. The Graeb score assigns a score ranging from 0 to 12, where 0 means no intraventricular hemorrhage and 12 means that all four ventricles are filled with blood [3].

Using the Graeb score, MRI and CT had the same Graeb scores in 72% of the pair imaging but the MRI had a higher Graeb score in 24% of the cases [3]. When comparing the Graeb scores, the MRI had consistently higher scores than CT [3]. MRI was 100% sensitive but CT failed to detect the intraventricular hemorrhage in 3% of the cases [3].

Conclusion

Both CT and MRI allow for effective imaging of brain tumors and infections. For neurological infections both CT and MRI imaged the infections but the MRI was considered the better imaging modality because it was more specific and could detect infection symptoms that the CT may fail to detect [1]. MRI can image in multiple planes and has superior contrast resolution but CT also effective in detecting calcification related to a tumor [1]. Specific and high contrast neuroimaging is crucial for diagnosing neurological infectious diseases and could potentially reduce the mortality due to nervous system infections [1]. MRI is superior in detecting nearly all neurological infections and is preferred over CT when available [1]. Accurate and sensitive imaging from imaging modalities such as CT and MRI is extremely important and can be life saving in the case of bacterial and parasitic infections and brain hemorrhage diagnostic.

The identification of an association between the brain activity and the suicidal behavior is crucial for identifying prevention methods [2]. Because of its high contrast and different features, MRI can help better understand brain patterns relevant in suicidal behavior for better treatment and prevention [2]. As a neuroimaging modality, MRI can be further improved for structural and functional imaging in order to develop intervention responses [2].

MRI was more sensitive for identifying intraventricular hemorrhages than CT.

MRI identified the presence of intraventricular hemorrhages in cases where CT did not [3]. Intraventricular hemorrhage is detected to a much greater extent by MRI [3]. In the case, the choice of MRI instead of CT for diagnosing hemorrhages is extremely important and can be life saving since intraventricular hemorrhages can be deadly [3].

Discussion

We examined the use of CT and MRI as neuroimaging modalities for bacterial and parasitic infections and to study the association between white matter hyper intensities and suicidal behavior; and finally for the identification and quantification of intaventricular hemorrhages. For neurological infections MRI was found to be a much superior modality for imaging most neurological infections unless the infection caused calcification in which case CT is more specific. For white matter study , only MRI was used to show an example of the extent of the applications of MRI and how it can be applied for psychological purposes where contrast is key because it is inherently difficult to discriminate between grey and white matter in the brain. MRI has a much higher contrast than CT. Lastly, we examined and compared both MRI and CT for intraventricular hemorrhage detection and quantification [3]. Compared to CT, MRI is a more sensitive intraventricular hemorrhage imaging modality since CT failed to diagnose the condition in 3% of the cases [3]. CT Had lower Graeb scores than MRI which means that CT showed less intraventricular blood that the MRI [3]. This proves that CT and MRI cannot be used interchangeably with MRI because MRI is superior for the diagnostic of intraventricluar hemorrhage [3].

In the intraventricular hemorrhage research, a limitation could be the presence of a pathology that could mimic the hemorrhage symptoms thus creating false-positives results in MRI. In this case the MRI sensitivity of 100% would be incorrect [3]. Another limitations could come from the fact that the CT and MRI neuroimaging were not done simultaneously and the intraventricular hemorrhage could grow in that time period [3]. This could be significant considering that MRI scans were usually performed after the CT scan which would be responsible for a larger volume of blood and thus the higher sensitivity for the MRI [3]. However, the time between when the patient developed the symptoms and when the MRI scans were done was on average more than 30 hours which is larger than the expansion time a hemorrhage [3].

CT and MRI are both imaging modalities for visualizing the brain. Each modality has advantages and disadvantages. Time and economic considerations also contribute to the choice of the modality [4]. CT scanning for instance takes less time, and are more comfortable and cheaper than MRI. The CT machines are also more widely available than MRI [4].

A new type of device could be even better than both MRI and CT as far as intracerebral hemorrhages are concerned [5]. Intracerebral hemorrhages are deadly and the secondary expansion and bleeding are quite common [5]. A non-invasive, portable device would allow for continuous monitoring of intracerebral hemorrhages [5]. The power received by the antenna is measured before and after a intracerebral hemorrhage and the difference in the received power between normal and after the hemorrhage allows for the detection [5]. Compared to imaging modalities such as MRI and CT, this device does not require professional personnel to use the equipment [5]. It is easy to use and does not require any dye or contrast agent [5]. This device has the potential to significantly improve neurological in brain injured patients that require continuous monitoring [5].

References:

[1] Raibagkar et al. 2014. Imaging in Neurologic Infections I: Bacterial and Parasitic Diseases. Curr Infect Dis Rep (2014) 16:443

[2] Ehrlich et al. 2005. White matter hyperintensities and their association with suicidality in depressed young adults. Journal of Affective Disorders. Volume 86, Issues 2–3, June 2005, Pages 281–287

[3] Romanova et al. 2014. Magnetic Resonance Imaging Versus Computed Tomography for Identification and Quantification of Intraventricular Hemorrhage. Journal of Stroke and Cerebrovascular Diseases. Volume 23, Issue 8, September 2014, Pages 2036–2040

[4] Kromhout et al. 2014. Low-Field MRI and Multislice CT for the Detection of Cerebellar (Foramen Magnum) Herniation in Cavalier King Charles Spaniels. J Vet Intern Med 2014.

[5] Kandalai et al. 2014. In vivo testing of a non-invasive prototype device for the continuous monitoring of intracerebral hemorrhage. Journal of Neuroscience Methods

Volume 235, 30 September 2014, Pages 117–122.

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