# An Efficient Automatic Midsagittal Plane Extraction in Brain MRI
## 1 Introduction  
Segmentation of brain in magnetic resonance images (MRIs) is one of the difficult and crucial steps of clinical diagnostic tools in medical images. The brain is the most complex organ in the human body that can be split into two approximately symmetrical hemispheres using a plane. This plane is known as the midsagittal plane (MSP) [1]. In brain symmetric/asymmetric analysis, automatic MSP extraction that is independent for symmetrical and asymmetrical brain regions is an essential brain segmentation task [2]. Enormous research reflects that the symmetrical structure of the brain deteriorates due to psychological and physical ailments in the brain [3]. Clinical experts use the symmetry of the brain to identify qualitatively asymmetric patterns that signify an ample range of pathologies, such as brain tumors [4; 5], brain infections [6], metabolic disorders [7], brain injury [8], and perinatal brain lesions [9]. Similarly, the computer-aided diagnostic and image analysis systems can use the symmetry and asymmetry information as a prior knowledge to embellish the system efficiency in the analysis of altered brain anatomy [10]. Moreover, the detection of MSP is required in registration [11] of medical images as the first step for spatial normalization [12] and anatomical standardization [13] of the brain images. However, legitimate evaluation of symmetric and asymmetric patterns in brain images is possible only when the symmetry axis or the symmetry plane (MSP) is accurately aligned and appropriately oriented within the coordinate system of the MRI scanner [14]. This permits the system to adjust the possiblemisalignment of brain MRIs. A general phenomenon in brain MRI scanning is that many neuroimaging scanners produce tilted and distorted brain images. The tilt of the head is not always detectable, due to many reasons such as the health conditions, immobility of patients, imprecision of the data calibration systems, and the inexperience of the technicians. Consequently, the slices of the brain MRIs are no more alike within the same orientation, at either the axial or coronal level [15]. Disoriented and misaligned brain MRIs can betray visual inspection and prevalently yield erroneous clinical perception [16]. In summary, assessment of brain MRIs for any anomaly based on cross-referencing of brain hemispheres (left and right), either by a human expert or computer-based software could be affected by false geometrical representation. Consequently, it is essential to correct the tilt and realign the brain MRIs data before further analysis. Manual misalignment correction is extremely time-consuming and laborious to perform on a huge scale. It also demands an urbane knowledge of brain anatomy. Therefore, it is neither sufficient nor efficient. Alignment or tilt correction of brain MRIs is tantamount to realigning the MSP with the center of the image matrix or image coordinate system [14]. If the MSP is computed precisely, the orientation problem of the MRI volume can be resolved. Thus, the tilt of the head volume can be assessed and adjusted. An ideal MSP can be defined as a virtual geometric plane passing through the interhemispheric fissure (IF) [17], about which the three-dimensional (3-D) anatomical structure of the brain (such as the ventricles, anterior/posterior commissures, corpus callosum, thalamus) exhibits maximum bilateral symmetry [18]. Previously, several approaches that considered the problem of computing the MSP in brain MRIs and other brain image modalities (Computed Tomography (CT), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT)) have been published. These approaches can be divided into two distinct groups, varying in their exclusive interpretation of prescribed MSP: (1) shape-based algorithms that identify the location of cerebral IF using features of the head images to estimate MSP; and (2) content-based algorithms that considered MSP as the plane which maximizes the bilateral symmetry of the brain.