الفهرس 
Anatomy of regions of interest (R O Is)
Imaging principles in computed tomography (Only 14 pages are availabe for public view
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Abstract
The structure of the orbit is affected by several orbital diseases such as congenital orbital dysplasia, orbital fracture and intraorbital tumor. Deformation of the orbit results in apparent physical signs such as enophthalmos and exophthalmos and may also lead to serious disequilibration of bilateral craniofacial development. The measurements of the orbital walls and volume have important clinical applications as estimating craniofacial asymmetry, the severity of the injury and possible complications in preoperative planning and in postoperative evaluation Aim of the work: The present study aimed to assess the morphometric and volumetric variations of human’s bony orbit by using CT and MRI. Also, it was performed to assess the volumetric relation between orbit, eye ball and morphology of frontal and occipital cerebral cortex by MRI. Subjects and methods: Evaluation of the orbit was done on 80 healthy individuals of both sexes aged from 20 to 60 years by two different methods. 1. Thirty healthy individuals including males and females were evaluated for the morphometric analysis of the distances of orbital bony walls and the dimensions of the orbit by (MsCT) as follow: Superior orbital wall was measured by two distances: • One from supra orbital notch (SON) to the beginning of superior orbital fissure (SOF). • The other from supra orbital notch (SON) to the entrance of optic canal (OC). B. Inferior orbital wall was measured by two distances: • One from zygomatico maxillary suture (ZMS) to the entrance of optic canal (OC). • The other from zygomatico maxillary suture (ZMS) to the beginning of inferior orbital fissure (IOF). C. Lateral orbital wall was measured by two distances: • One from fronto zygomatic suture (FZS) to the beginning of superior orbital fissure (SOF). • The other from fronto zygomatic suture (FZS) to the entrance of optic canal (OC). D. Medial orbital wall was measured by two distances: • One from anterior lacrimal crest (ALC) to the entrance of optic canal (OC). • The other from anterior lacrimal crest (ALC) to the posterior ethmoidal foramen (PEF). Determination of orbital dimensions included the following: 1. Orbital width (OW) of its entrance. 2. Orbital height (OH) of its entrance. 3. Orbital depth (OD). 4. Orbital index (OI). 2. Fifty healthy individuals including males and females were evaluated for orbital, eyeball volumes and their relation to the cortical gray matter volume of frontal and occipital lobes by Magnetic Resonance Imaging (MRI). The study was done at CT & MRI scanning units at Radiology Department, Tanta University Hospital. The machines were (GE) optima 660 (128 Multidetector Computed Tomography MDCT) and a Toshiba Aquilion one (320 MDCT) and GE signa 1.5 Tesla system and Toshiba Titan vantage 1.5 Tesla system. The CT images were transferred to a personal computer (PC) workstation using RadiAnt DICOM viewer 4.6.9 software that provides reliable morphometry of the walls of bony orbit. The MRI images were transferred to a personal computer (PC) workstation using the slicer 4.8.1 software that provided reliable morphometry of orbit and eyeball by manual and semiautomated tracing. Volumetric analysis was done using 3D T1- weighted images for the regions of interest (orbit and eyeball) and the effect of side, age and sex differences were evaluated. Frontal and occipital gyri thicknesses and volumes were calculated using two different cortical parcellation tools by FreeSurfer software. This was performed to provide a better understanding of how the orbit and eyeball varied in relation to frontal cortical gyri and visual cortical gyri. Data were analyzed by student’s paired t test, student’s unpaired t test and regression analysis. Results of the present study: 1. Morphometric measurements of the orbit using computed tomography (CT). ▪ There was significant difference between right and left sides in superior orbital wall lengths measured between supraorbital notch (SON) and entrance of optic canal (OC.) in males. There were insignificant differences between the lengths of the right and left orbital walls in females. ▪ Regarding sex, there were highly significant differences of measured lengths of superior, lateral and medial orbital walls between males and females. ▪ Regarding age, it was found that with increasing age, there was decrease in the lengths of superior orbital wall in males but increase in the measured lengths in females. With increasing age, there were insignificant changes in measured lengths of inferior orbital walls in males and females except the measured distance between ZMS and IOF in males. With increasing age, there were insignificant changes in the measured lengths of lateral and medial orbital walls in males and females. ▪ There was significant difference in orbital index between right and left males’ orbits, but there were insignificant differences in all orbital dimensions between right and left females’ orbits. ▪ Regarding sex, there were highly significant differences between male and female orbits in the orbital entrance width and orbital depth and insignificant difference between male and female orbital entrance height. The orbital index was greater in females than males. ▪ Regarding age, it was found that with increasing age, there were insignificant changes in the width, height of orbital entrance and orbital depth in males and females.