College of medicine Department of radiology
CT SCAN IMAGINGComputerized tomography ( CT scan ) Introduction Tomography is one of the imaging investigation , it present from 1960 . Mechanism of Action : Tomography is the technique of rotating a radiation detector around the patient so that the image obtained gives additional three- dimensional information . In plain film tomography the source of XR ray & the photographic film move around the patient to produce an image of the structures at a particular depth within the body , bringing them into sharp focus , while deliberately blurring ( unclear ) structures above & below them . In computerized tomography , the same technique of usual tomography , but instead of film , there is detectors which attach to computer , this detector will catch the signal & convert it into pulse , then to computer as image of different section . So CT scan is a form of XR examination , in which the source & detector ( CT scanner ) & the information obtained can be used to produce cross sectional image ( i.e. CT scan can produce an image of slice through the body at a particular level )
N.B. when the no. of the detector increase , the clearance of the image is increase , the usual no. of detectors is used now about 400 .
The higher the thickness , the higher the Molecular weight , the more the absorption of the XR & more attenuation examples : Bone : is highly attenuated material , because it absorbed much XR so it appear white in color . Soft tissues have less attenuation , so appear gray in color . Air has low absorption & low attenuation so it appear black in color .
Brain Anatomy and Images normal brain anatomy
normal brain ( anatomy ) Cerebral hemisphere Frontal lobe Parietal lobe Temporal lobe Occipital lobe Posterior fosse Cerebellum & brain stemVentricular system Lateral ventricle ( frontal horn , body ,temporal horn ,& occipital horn ) . Third ventricle . Fourth ventricle .
Pituitary fosse
anterior cliniod process the region of the sella tursica posterior cliniod process channel like area black in color ( cerebello pontine angle ) lesser wing of the sphenoid bone & below it immediately the greater wing of spheniod .CT terms Iso dense , same density to organ examine Hyper dense higher than the organ examined Hypo dense lower than the organ examined Density levels of different types of tissues Density levels of almost all soft tissue organs lie within a range 10-90 HU , Water density 0 HU , fluid 10-15 HU depending on their density , air -1000 HU , fat -100 - -50 HU , bone & calcification 100 & above HU , ossification 1000 & even more HU depending on the density
Herpes encephalitis same as usual encephalitis but there will be low attenuation or hypo density area in the tempo frontal or tempo priato frontal with evidence of patchy whitish area due to the clotted blood ( hemorrhage ) .
Brain abscess CP : high fever for long duration with focus of infection , patient may be toxic , or present with epilepsy( focal ) CT finding Hypo dense area surrounded by large area of peri focal edema, which may cause shifting of the midline ) . After injection the lesion show ring pattern of enhancement so the peripheral aspect of the lesion become more clear . DDx Secondary metastasis , patient have history of primary malignancy , beside absence of the fever . Primary necrotic tumor , neither Hx of primary , nor fever are present .
ACUTE INFARCTION * wedge shape hypo density area . * Shifting of the midline & frontal horn
Chronic infarction Hypo density area ( pore encephalic cyst ) Dilated ventricle
Hemorrhage Classify the brain hemorrhage according to the site : Epidural EDH Subdural SDH Sub arachnoids SAH Intra cerebral ICH Intra ventricular IVH Other classification according to the onset of bleeding : Acute Chronic
Acute EDH CT finding Hyper density area , 50-70 HU ,due to the clotted blood, elliptical in shape , no edema around the lesion , but may cause shifting of the midline , or compression of the ipsi lateral ventricle if it is large enough . The source of bleeding of the haematome is injured middle meningeal artery so the lesion > 90 % associated with skull # at the site of the previous mentioned artery .
EDH Biconvex hyper density area Shifting of the midline Compression of the ventricles
Acute Intra cerebral hematoma CT finding :Hyper dense area , surrounded by edema , any where within the brain parenchyma .Shifting of the midline Compression of the ipsi lateral ventricle .Associated with infarction , # , trauma concussion , tumor …..Hypertensive Hemorrhage
Subarachnoid hemorrhage causes due to ruptured aneurysm over 90 % of cases spcially at the circle of Willis . ruptured AV malformation . trauma . CT finding hyper density is seen within the SAS ( hyperdense sulci , being filled with clotted blood ) opacified inter hemispheric fissure ( become white & more dense ) opacification of the falx cerebri .