Computed Tomography (CT)

Computed Tomography (CT). By Reham Ashraf Hussien Lecturer of Oral and Maxillofacial Radiology.

Computed Data are acquired digitally Tomography Showing only a Section or Slice.

[image] •Creation of 2D cross sectional images from 3D body structures.

CT System. A CT system mainly consist of 3 major components; the gantry, the computer and the operating console. The gantry; consists of the detector, the x-ray tube and the patient support couch..

[image] • Detector an•ay: Multiple cells in one or multiple rows Receive X-ray after passing the patient then send information to the computer.

[image] Pencil beam Multiple pencil beams Fan bean 2nd.

[image] Vonage A-ray tube Patient / e/ / Gererator/ / ///Colimator,.'c/ Pre-patient Collimation Post-patient Collimation Patient // Collimator/" Detector Patient Patient dose Slice thickness Scatter _ [Ivate Windc.

[image] The Computers The detectors measure the x—ray beam intensity emerging from the patient and convert this into digital data stored & manipulated by the computer. Requirements??.

[image] Basic concept of CT scan X-ray beam Thin patient slice Scatter/absorption/transmittion in the patient Detectors collect transmitted x-ray Signals are digitized by the computer Image reconstruction Image display ind Go to S gs to a'.

[image] Body Planes Axial Sagittal Activate WI Go to Settings Coronal.

Axial. [image]. [image]. [image] iu!uas 01 0. [image].

Coronal. [image]. [image] ctivate '. [image].

Sagittal. [image]. [image].

Image formation. Data Acquisition Image Reconstruction Image Display, manipulation & storage.

[image] Data Acquisition The detectors measure the x-ray beam intensity emerging from the patient and convert this into digital data manipulated by the computer.

[image] Slice by Slice @ The gantry stops and unwind to return to zero position @ Patient support couch moves to allow examination of another slice of area of interest (--iö-wSettin.

[image]. [image] spiral CT -The gantry rotates around the patient in one direction without need for winding, stop and unwinding -Patient support couch moves in a smooth continuous motion rather than stopping for eac slice.

[image] Multislice CT Single Row Detectors row of detectors Single Slice Spiral Multiple Row Detectors Multiple rows of detectors Activate Winc Go to Settings to.

[image] Image Reconstruction The collected data Special mathematical techniques Digital image Activate Go to *tin'.

[image] Cngnal t.'mn sliced Primary reconstruction To give axial cuts Secondary reconstruction ro give cuts in different planes Activat Setting:.

[image] IMAGE OF PIXELS PIXEL Image Display Pixel: The unit forming the CT image Voxel is the 3-D analog of a pixel. Voxel size is related to both the pixel size and slice /Activate Wind0' Go to Settings to acti'.

After completion of scanning, the computer calculates the absorbed x-ray beam at points on matrix (formed of pixels). The numerical data at any pixel called CT number (Hounsfield unit). Huounsfield unit is depending on the amount of absorption within tissue in relation to the water when radiographed..

[image] Hounsfield Units H2 3000 bone • fat +1000 -50 - -100 -1000 air -1000 soft tissue lungs +40 - +80 -400 - -600 CT number (Houns41eld Unit) It corresponds to the linear attenuation coefficient of a particular tissue in relation to that of water at a given kilovoltage and ranges from -1000 to +3000.

[image] Windowing In 111 111 111 111 111 111 111 111 111 Window selected for the various grey shades to be displayed Window level: the central value of this range CT no. outside the window width wil appear white above the window or black if below the window.

[image] 1 50 22.4 512 'WOO:' Tower AIMEE 031Y F 3 '4 44.30.0 16 :atoejd 20 esot it2 tn.o:t AIMEE e 032M F 38 200SFi 3938 ctivate W to to Settings.

Applications. Buccolingual dimension ▪ Relation to vital structures ▪ Bone density by Hounsfield number ▪ Computer guided implantology.

Maxillofacial Trauma. Fracture lines Detection (Number, Location, Type, Extension, Displacement) Presence of foreign body ▪ TTT plan.

Maxillofacial lesions. Full extension Relation to vital structures Third dimension Lesion effects as expanssion, erosion , perforation, invasion.

Tempromandibular Joint. Fractures at condylar neck Displacement degree & direction Ankylosis Tumors Calcifications Anomalies Hypoplasia Hyperplasia Bifid condyle.

Salivary gland lesions. Early stone detection (Small stones with decreased calcification) ▪ Inflammatory diseases ▪ Cysts & neoplasms.

Maxillary sinus. Sinusitis Lesions. [image] COY. [image] netivate o to Setting.

Infections. Extensive infection Early detection of acute cases before conventional radiographs Actual lesion extension.

Advantages. Minimizes the superimposition Good soft tissue resolution Record small differences in tissue densities.

Images reformation Image manipulation & enhancement.

Limitatioms. High dose of radiation. No direct sagittal images. Direct coronal is limited in case of cervical abnormalities, Contrast resolution of soft tissue is lower than MRI. ..

Spatial resolution is lower than conventional radiography. High cost. Sensitive to technique errors. Special training is required for interpretation.

Thank you.