Computed Tomography (CT) Scan
CWHAT IS A CT SCAN?
omputed Tomography (CT) is an imaging method that uses x-rays and computer to create crosssectional pictures/images of the body. It has been used as medical imaging since 1972 and has evolved into the 4th generation presently. CT has developed from single slice CT to multi-slice CT (MSCT) and dual source CT over a duration of 39 years. There is great improvement in speed, patient comfort and resolution with the present generation of CT. With this advanced technology, CT provides excellent image quality for diagnostic confidence at the lowest possible radiation dose. A whole body CT will take about 30 seconds to complete with 64 MSCT. CT provides greater clarity and reveals more details than regular xray/ultrasound exams of internal organs, bones, soft tissue and blood vessels. It helps doctors and radiologists to diagnose cancers, cardiovascular disease, infectious disease, appendicitis, trauma, musculoskeletal disorders etc.
WHAT ARE THE USES OF CT?
CT can be used to scan any part of the body. It is one of the best and fastest tools for studying the chest, abdomen and pelvis because it provides detailed, cross-sectional views of all types of tissue. Commonly done CTs are head, neck, chest, abdomen and pelvis. CT is mainly used to solve clinical problems. Physicians often use CT examination to: Quickly identify injuries to the lungs, heart and vessels, liver, spleen, kidneys, bowel or other internal organs in cases of trauma. Guide biopsies and other procedures such as abscess drainages and minimally invasive turmour treatments. Plan for and assess the results of surgery, such as organ transplants or gastric bypass. Stage, plan and properly administer radiation treatments for tumour as well as monitoring the response to chemotheraphy. With tremendous research and development in CT, health screening using CT is gaining momentum and is more acceptable. New generation of CT offers good diagnostic image quality with low radiation dose. Currently, low dose CT lungs, CT colonography and cardiac CT for calcium scoring and coronary angiogram can be offered as health screening tool with guidelines. Many studies had proven that these screening CT help to reduce morbidity and mortality as well as healthcare cost. Lung cancer is the 3rd commonest cause of cancer death in Malaysia. In the United States, the lifetime risk of developing invasive lung cancer is 1 in 17 for men and 1 in 18 for women. It is estimated that over 80% of lung cancers could be cured if detected at an early stage. CT is more sensitive than chest X-ray in detecting lung cancer. Studies show that there are 20% fewer lung cancer deaths in those screened with low-dose MSCT compared to chest Xray.
The indications for screening CT lungs are:
History of lung cancer 10 packs/year or more smoking history (1 pack of cigarettes per day for 10 years, 2 packs of cigarettes per day for 5 years, etc.)
Past history of smoking (less than 10 years ago)
Repeated exposure to secondhand smoke Exposure to other cancer-causing agents (e.g. asbestos and radon)
Age more than 40 years Colorectal cancer is the 2nd commonest cause of death due to cancer in Malaysia. Colorectal cancer is the third most common cancer diagnosis in the United States and the second leading cause of cancer-related deaths. Each year, about 150,000 people are diagnosed with colon cancer, and about 50,000 will die of it. However, if detected early, the 50-year survival rate for colon cancer exceeds 90%. Recent data studies showed CT colonography is comparable to optical colonoscopoy for the detection of cancer and polyps of significant size (more than 1 cm).
The indications for CT colonography screening are:
Older than 50 years
Have had polyps in the past
Family history of colon cancer
Test positive for blood in the stool Elderly patients who are frail or infirm – difficult for colonoscopy. When colonoscopy is attempted but incomplete because the full lenght of the colon is not visualised, CT colonography may be done on the same day. If a tumour is found on colonscopy and it blocks passage of the scope, CT colongraphy will permit a thorough check of the entire colon.