What is CT Scanning?
CT scanning uses several computer and takes X-ray images of structures of human or animal from different angles and it produces a cross sectional image of the scanned object. Then it is converted into images and can be monitored using a monitor. It allows the user to view the images inside the body without cutting. CT Scanning shows the images of organ, bones, and tissues. It produces three dimensional images of scanned object using a three dimensional object. i.e, many images of same area from different angles are taken and the combination of these gives idea about the three dimensional view. Computer program is used to create these images. The main application of CT scanning is medical imaging. The CT scan images can be used for diagnostic purposes and medical applications. It is also used in industrial applications i.e, industrial computer tomography scanning. There are different types of CT scanning such as X-Ray CT, Positron Emission Tomography (PET), Single Photon Emission Computer Tomography (SPECT), etc. Tomography came from combination of Greek word tomos and graphein. Tomos means cut or slice of a section and graphein means record or to write. It is used to get clear and detailed image of body parts such as tissues, lungs, brain, abdomen etc.
CT Scanning is also used for diagnosing cancer, the exact size, its correct location, affected tissues etc.
The patient lies on the table. This table will move at a constant speed during scanning period. The X-ray tube and detectors are in idle condition. CT scanning is same as that of X-ray which is either in a 6-12 clock position or 3-9 clock position. When the CT scanning starts, the computer will instruct gantry to rotate in a desired orientation. The patients table is controlled by a computer. The x-ray generation and detection system, image generation system etc. are controlled by the computer. During the complete CT scanning operation, the patients table moves in a constant speed. It consists of a high voltage generator and it will reach upto the desired limit. It will maintain both voltage and current to the X-ray tube at the desired level during CT scanning operation. An x-ray flux is produced by the x-ray tube and the x-ray detector is used to detect the photons and it will produce electrical signals. The output from the x-ray detector is sampled using data acquisition system. The analog signal is converted into digital signal. This data after sampling will be given to the image generation system. The system contains high speed computers and digital signal processing chips. After processing the data, it will be displayed in the display device. And this data is stored in the data storage device.
The CT scanning will emit a series of beams through the human body. Its image is far better than X-Ray image. It consists of X-Ray detector. It helps to view the tissues of an organ. The 3-D image of body part is build up according to the data received in the computer. This image is displayed on the screen. To have a clear view, a contrast dye can be used.
The patient lies down the monitorized table and it goes into the doughnut hole of the CT scanning machine. Before that the patient must remove the jewelry items. The patient lies in a way that the face is up otherwise face is down or it lies in sideways. To get the correct images the patient must lie without any movement. The contrast dye is given as enema, or injected or swallowed for improving the images of blood vessels, organs or tissues. To take the 3-D image of abdomen, the patient has to drink barium. This barium moving through the digestive system shows a white on the scan. To take image of the lower down part of body such as rectum, a barium enema is given to the patient. To take the images of blood vessels, the barium is injected. In Spiral CT scanning, the X-Ray beam flow in a spiral path while scanning. It has high accuracy and high speed. It takes continuous images without delay. To take the spiral scan of chest, the patient needs to hold the breath for few seconds. The scan images of head gives clear idea about swelling, bleeding etc. in brain. The scan images reveal any tumor in abdomen. It shows if there is any swollen in the internal organs. It also gives idea about the vascular conditions (blood flow) of patient. The vascular conditions cause stroke, kidney failure etc. It also gives information about the injuries in body parts as well as skeletal parts. A small bone and surrounding tissues can be clearly viewed in these scanned images. At first the CT scanning machines rotate the source and detectors around the patient which lies down on the monitoring table. After complete rotation, the object (patient) moves along its axis. After that, it starts the next rotation. To capture multiple cross sections at the same time, multiple rows of detectors are used instead of single rows. The data obtained gives a visual representation known as sinogram. But this sonogram is not sufficient for interpreting this. So the data is processed for interpretation by using tomographic reconstruction. It will produce a series of cross-sectional images. The radiologists will analyze the CT scanning images and gives the detailed report to the doctor.
Reconstruction of CT Scan Images
Multiplanar reconstruction: - It is the simplest method of reconstruction. The different slices is stacked to build the three dimensional image. The individual slices are stacked by using some software program.
CT Scan of different body parts are:
- Head:- The CT scan image of head is used to detect tumors, bone trauma, infarction etc. If there is any swelling is detected or some distortion, then it is clearly detects the tumor. If there is any disjunction in bone, then it is clearly detects the bone trauma. If there is any dark structure in the image, it clearly shows infarction. When MRI is not available, then the CT images may also used for the evaluation of headache. The CT scan of brain from skull base to the top is given below.
- Lungs: - The CT scanning of lungs can be used to detect acute changes in the internals of lungs (Parenchyma). The X-Ray images cannot show such defects. There are different techniques for detecting the abnormalities. Scan of inspiration and expiration is taken. It easily represents the tumor.
- Cardiac CT Angiography: - It has high speed and high resolution simultaneously. It gives clear image of coronary arteries.
- CT Pulmonary Angiogram (CTPA):- It is a diagnostic test which is used to diagnose pulmonary embolism. It gives the image of pulmonary artery.
- Abdominal and Pelvic CT: - It can be used for diagnosing abdominal diseases. It determines the cancer stages and also used to evaluate the acute abdominal pain.
- It can easily recognize the fractures, injuries and dislocations. The CT scan images create the images of fractures etc.
It has a lot of advantages. It mitigates the super imposition of images outside the area of interest. It can easily recognize very minute changes due to its high resolution.
The radiation causes damages of body cells such as DNA molecules which lead to cancer. The radiation for CT scan is very high compared with the conventional X-Ray images. Researches show that the radiation adversely affects the health conditions.