**2. Magnetic Resonance and Magnetization Transfer Imaging**

The morphological MRI acquisitions usually include non-contrast-enhanced sagittal T1, axial diffusion, axial fluid attenuated inversion recovery (FLAIR), axial T2-SE, coronal T2 sequences and a 3D T1-weighted volume acquisition. FLAIR and T2-SE sequences permit to detect brain edema, contusion, hematoma, herniation, subarachnoid hemorrhage, or hydrocephalus. T2 sequences are useful in detecting hemorrhagic diffuse axonal injuries (DAI). The total number of lesions detected by FLAIR and T2 are shown to be inversely correlated with Glasgow Outcome Scale (GOS) of traumatic coma patients; while the 3D T1 sequence provides an opportunity to evaluate the brain atrophy during the follow up of these patients. A lot of studies performed on traumatic coma patients with conventional MRI showed that lesions of the pons, midbrain, and basal ganglia were predictive of poor outcome especially when they are bilateral. Despite their encouraging results, these studies fail to explain why some patients in VS or with long-term marked cognitive impairments have no or minimal lesions on conventional MRI examination. This raises the question of the lack of specificity and insufficient sensitivity of conventional MR sequences which fail to reveal lesions such as ischemic axonal injuries. Therefore, it is clear that morphological and conventional MRI alone cannot be considered as a reliable tool to assess consciousness disorders severity or to predict their evolution and outcome (Tshibanda et al., 2009). Several studies investigated patients in VS and in MCS using non-conventional, quantitative and volumetric MR techniques, useful to provide information about the anatomical patterns, the prognosis and the outcome of these patients. Ammermann et al. (2007) have used volumetric analysis of MRI to determine the pattern of lesions in 12 patients with a severe neurological impairment after acute ischemic injury. At the time of scanning, the patients were either in VS or in an early remising state, that is MCS. Lesions were classified as having been present in the gray and/or white matter in four different brain regions (frontal, parietal, temporal, occipital). An additional separate evaluation was performed for the basal ganglia, thalamus, hippocampus, cerebellum, and brainstem. The total clinical follow-up period of all patients from the time of the causative event lasted for at least 5 months. The clinical outcomes were reported according to the Rancho Los Amigos Cognitive Scale (RLACS) as a universal guide to assess a patient's level of functioning. The final RLACS levels were correlated to the MRI lesion size with a Spearman correlation. All patients demonstrated extensive white matter lesions, with the largest lesions observed in the frontal and occipital lobe. A preferential involvement of the white matter located in the periventricular area and in the subcortical regions below the motor and internal temporal cortices was found, in addition to the classifically described lesions of the striatum, motor and occipital cortices. Lesion magnitude showed an association with the severity of the outcome as quantitatively assessed by RLACS. With respect to gray matter lesions, the vulnerability pattern observed included frontal and occipital and in some cases parietal cortical areas, moreover in most cases the thalamus. Additionally, almost all of patients showed lesions of the hippocampus or lesions to the basal ganglia. An association between the extent of the MRI defined lesions located within the white matter and the clinical

fMRI), MR spectroscopy (MRS), diffusion tensor imaging (DTI), fiber tracking, positron emission tomography (PET)) that serve as complementary clinical tools that may help differentiate the effects of underarousal, sensory impairment, motor dysfunction, and cognitive disturbance in the search for potential causes of behavioural unresponsiveness.

The morphological MRI acquisitions usually include non-contrast-enhanced sagittal T1, axial diffusion, axial fluid attenuated inversion recovery (FLAIR), axial T2-SE, coronal T2 sequences and a 3D T1-weighted volume acquisition. FLAIR and T2-SE sequences permit to detect brain edema, contusion, hematoma, herniation, subarachnoid hemorrhage, or hydrocephalus. T2 sequences are useful in detecting hemorrhagic diffuse axonal injuries (DAI). The total number of lesions detected by FLAIR and T2 are shown to be inversely correlated with Glasgow Outcome Scale (GOS) of traumatic coma patients; while the 3D T1 sequence provides an opportunity to evaluate the brain atrophy during the follow up of these patients. A lot of studies performed on traumatic coma patients with conventional MRI showed that lesions of the pons, midbrain, and basal ganglia were predictive of poor outcome especially when they are bilateral. Despite their encouraging results, these studies fail to explain why some patients in VS or with long-term marked cognitive impairments have no or minimal lesions on conventional MRI examination. This raises the question of the lack of specificity and insufficient sensitivity of conventional MR sequences which fail to reveal lesions such as ischemic axonal injuries. Therefore, it is clear that morphological and conventional MRI alone cannot be considered as a reliable tool to assess consciousness disorders severity or to predict their evolution and outcome (Tshibanda et al., 2009). Several studies investigated patients in VS and in MCS using non-conventional, quantitative and volumetric MR techniques, useful to provide information about the anatomical patterns, the prognosis and the outcome of these patients. Ammermann et al. (2007) have used volumetric analysis of MRI to determine the pattern of lesions in 12 patients with a severe neurological impairment after acute ischemic injury. At the time of scanning, the patients were either in VS or in an early remising state, that is MCS. Lesions were classified as having been present in the gray and/or white matter in four different brain regions (frontal, parietal, temporal, occipital). An additional separate evaluation was performed for the basal ganglia, thalamus, hippocampus, cerebellum, and brainstem. The total clinical follow-up period of all patients from the time of the causative event lasted for at least 5 months. The clinical outcomes were reported according to the Rancho Los Amigos Cognitive Scale (RLACS) as a universal guide to assess a patient's level of functioning. The final RLACS levels were correlated to the MRI lesion size with a Spearman correlation. All patients demonstrated extensive white matter lesions, with the largest lesions observed in the frontal and occipital lobe. A preferential involvement of the white matter located in the periventricular area and in the subcortical regions below the motor and internal temporal cortices was found, in addition to the classifically described lesions of the striatum, motor and occipital cortices. Lesion magnitude showed an association with the severity of the outcome as quantitatively assessed by RLACS. With respect to gray matter lesions, the vulnerability pattern observed included frontal and occipital and in some cases parietal cortical areas, moreover in most cases the thalamus. Additionally, almost all of patients showed lesions of the hippocampus or lesions to the basal ganglia. An association between the extent of the MRI defined lesions located within the white matter and the clinical

**2. Magnetic Resonance and Magnetization Transfer Imaging** 

outcomes of the patients was found. All patients in the most unfavorable class III clinical outcome group (i.e. persistent VS) exhibited white matter lesions exceeding 2/3 of the volume of at least one lobe, most frequently the occipital lobe.

Moreover, Juengling et al. (2005) investigated 5 patients in persistent VS due to prolonged cerebral hypoxia of non-traumatic origin, using combined Voxel-Based Morphometry (VBM) of 3D MRI and FDG-PET analysis. In the analysis of the regional distribution of gray matter atrophy, VBM revealed multiple areas of significantly decreased gray matter density at p<.001, corrected for multiple comparisons. Those were localized in multiple cortical areas, in particular including inferior parietal lobe, superior and medial frontal lobe, paracentral lobule, superior and medial temporal lobe, the cingulum, and the fusiform gyrus. Thalamic changes were limited to small voxel clusters in dorso-medial areas. These structural atrophic changes were compared with the local distribution of functional loss as assessed by regional hypometabolism in the FDG-PET group analysis. At the threshold pb0.001 (corrected for multiple comparisons), PET showed a widespread pattern of hypometabolic areas. In particular, the parietal and frontotemporal cortices, the cuneus/precuneus, the cingulum, the frontal medial and precentral gyrus, and the transverse temporal gyrus were involved, additionally the bilateral thalamus (mainly dorsomedial subnucleus). All changes were, similar to the VBM results, nearly symmetrical. Improved understanding of this complex lesion pattern gained by in vivo group analyses like here might help to provide deeper insights into the general pathoanatomy of patients in the persistent VS.

Using high-resolution T1-weighted magnetic resonance images and a novel approach to shape analysis applied SIENAX software, Fernandez-Espejo et al. (2010) investigated thalamic global and regional changes in a sample of patients in a VS or an MCS. They found that total thalamic volume was significantly lower in patients than in healthy volunteers. Shape analysis revealed significant bilateral regional atrophy in the dorso-medial body in patients compared to controls; this atrophy was more widespread in VS than in MCS patients. Lower thalamic volume was significantly correlated with worsening of Disability Rating Scale (DRS) scores. Shape analysis suggested that the dorso-medial nucleus and the internal medullar lamina were the main regions responsible for this correlation. These findings suggest that MCS and VS patients present different patterns of regional thalamic abnormalities. In particular, VS patients showed a more widespread pattern of atrophy than controls, producing differences in global thalamic volume. MCS patients did not show volumetric differences compared to controls, and regionally they showed a less pronounced inward collapse in both the dorsal and ventral areas, with the anterior-ventral body significantly spared. Neuropathological studies have demonstrated that thalamic damage is less common in MCS than in VS patients (Jennett et al., 2001).

Another quantitative RM technique is the Magnetization Transfer Imaging (MTI). The MTI relies on the principle that protons bound in structures exhibit T1 relaxation coupling with protons in the aqueous phase. When an off-resonance saturation pulse is applied, it selectively saturates those protons that are bound in macromolecules. These protons subsequently exchange longitudinal magnetization with free water protons, leading to a reduction in the detected signal intensity (Sinson et al., 2001). The MTI may provide a quantitative index of the structural integrity of tissue and might be useful to study the outcome of patients with low levels of consciousness.

However, further studies, on larger groups of patients, need to be performed to confirm the usefulness of quantitative MRI in the assessment of the eventual neurological prognosis and outcome of these challenging patients.

Neuroimaging and Outcome Assessment in Vegetative and Minimally Conscious State 185

metabolism. Two other patients with non‐anoxic, multifocal brain injuries demonstrated several isolated brain regions with relatively higher metabolic rates. A single patient who suffered severe injury to the tegmental mesencephalon and paramedian thalamus showed widely preserved cortical metabolism. The variations in cerebral metabolism in chronic VS patients indicate that some cerebral regions can retain partial function in catastrophically

fMRI is based on the increase in blood flow to the local vasculature that accompanies neural activity in the brain. This result in a corresponding local reduction in deoxyhemoglobin because the increase in blood flow occurs without an increase of similar magnitude in oxygen extraction (Roy & Sherrington, 1890; Fox & Raichle, 1985). Since deoxyhemoglobin is paramagnetic, it alters the T2 weighted magnetic resonance image signal (Ogawa et al, 1990). Thus, deoxyhemoglobin is sometimes referred to as an endogenous contrast enhancing agent, and serves as the source of the signal for fMRI. Using an appropriate imaging sequence, human cortical functions can be observed without the use of exogenous contrast enhancing agents on a clinical strength (1.5 T) scanner (Bandettini et al., 1992, 1993;

Functional activity of the brain determined from the magnetic resonance signal has confirmed known anatomically distinct processing areas in the visual cortex (Schneider, et al, 1993), the motor cortex, and Broca's area of speech and language-related activities (Hinke et al., 1993; Kim et al., 1995). Further, a rapidly emerging body of literature documents corresponding findings between fMRI and conventional electrophysiological techniques to localize specific functions of the human brain (Atlas et al., 1996; Detre, et al, 1995; George, et al, 1995). Consequently, the number of medical and research centers with fMRI capabilities

Several fMRI studies in the VS have confirmed the findings of previous PET studies. Di et al. (2007) used fMRI to evaluate differences between seven VS and four MCS patients in brain activation occurring in response to the presentation of the patient's own name, spoken by familiar voice (SON-FV). They prospectively studied residual cerebral activation to SON-FV in seven patients with VS and four with MCS. Two patients with VS failed to show any significant cerebral activation. Three patients with VS showed SON-FV induced activation within the primary auditory cortex. Only two of the VS patients, and all four MCS patients, showed activation not only in the primary auditory cortex but also in hierarchically higher-

Three months after fMRI examination, these two VS patients had progressed to the MCS. This study showed that fMRI measurement might be a useful tool for pre-clinically distinguishing MCS-like cognitive processing in some patients behavioural classified as vegetative. Schiff et al. (2005) have tested the hypothesis that MCS patients retain active cerebral networks that underlie cognitive function. fMRI was employed to investigate cortical responses in two male adults with severe brain injuries resulting to MCS and in seven healthy volunteers. Three passive stimulation tasks were performed: tactile stimulation, auditory narratives of familiar events presented by a familiar person, and the same auditory passages without language-related content. Results have showed a residual brain activity of cortical systems involved in a potential cognitive and sensory function

In conclusion, results of these studies we analyzed confirm the idea that PET and fMRI activation profiles may constitute useful adjunctive diagnostic methods when behavioral

despite their inability to follow simple instructions or communicate reliably.

injured brains.

Schneider et al, 1993).

and investigational programs continues to escalate.

order associative temporal areas.
