CT Scan

Tomography comes from the Greek tomos (slice) and graphia (describing).

What do The Beatles and CT have in common?


EMI recording studio developed the first CT scanner.

The idea of CT Scan, computed tomography, or CAT scan as some people like to say, has been around since 1967. Alan Cormack of S. Africa developed the theory behind CT. Godfrey Hounsfield of EMI in England developed the first scanner. These two scientists shared the Nobel Prize in Medicine in 1979 for their discovery.
The 1971 prototype from EMI took 5 minutes to scan each image and over 2.5 hours to reconstruct the image data.
The first commercial EMI scanner was used to image the brain in 1972 in Wimbledon, England. It took about 4 minutes to scan the brain and 7 minutes to reconstruct each image. And we complain when patients won't hold still now for 12 seconds!

CT uses X-rays to obtain images and a powerful computer to reconstruct and manipulate these images. The patient lies on the scanner table and moves horizontally into the gantry. Inside the gantry is the x-ray tube and detector array. This x-ray tube and detector rotate inside the gantry as the patient slides through on the table; we can scan any body part from head to toe. A routine brain takes approximately 12 seconds to scan. A routine chest takes about 10 seconds to scan. An entire chest, abdomen and pelvis can be scanned in approximately 18 seconds. It only takes a few seconds to reconstruct the image data.

Some more advanced uses for CT Scan include CT Angiography, CT Guided Biopsy, CT Guided Radio Frequency Ablation (RFA), and Virtual Colonography. Some of these procedures are performed by a Radiologist. Most are performed by a Medical Radiation Technologist (MRT) under the supervision of the Radiologist.

The scanner views your body like a loaf of bread. We can view axial images (like a cross-ways slice); sagittal images (like a lengthwise slice); or coronal images (like slicing the crust off). We can get really fancy when we do multiplanar reformats (MPR) or 3D imaging.

At MSH, there are 3 64 slice CT Scanners used in everyday operation. There is also 1 4 slice CT Scanner used for the Lung Screening Program, and as you read this entry, the 16 slice CT Scanner is scanning away in the Emergency department, operated by the Gen Rad team.

At PMH, there are 3 64 slice scanners. Two scanners run from 0800-2300hrs, Monday to Friday. The Gen Rad technologists are trained to scan Level 2 CT (single phase studies) and they are responsible for the daily operation of the other scanner. On an average, there are 80-90 patients scanned per day! For the most part, patients get the "PMH special": chest, abdomen, pelvis, head/neck with IV contrast-the works! This volume of patients would not be possible without one very special person- Stella, the CT assistant.


At TWH, the Medical Imaging department (specifically CT), the Neuroscience department as well as the Radiation medicine program work in conjunction to form Canada's first Gamma Knife centre. With the help of CT scans, beams of gamma radiation are targeted to areas of the brain where it's too dangerous or challenging to access.

There are 2 64 slice scanners on the 3rd floor operated by CT technologists and an 8 slice scanner in the Emergency department operated by General Radiography technologists. This is where the Regional Stroke Study centre relies on timely imaging of patients who might have had a stroke. If the stroke is detected in time, a special medicine is given to help in the recovery of patients.

At TGH, there are 3 64 slice scanners; one dedicated to Cardiac CT, where anatomy of the heart, coronary circulation and the great vessels are seen. The 3D lab team then will use the CT scan data to produce high resolution 3D images of the heart and great vessels like this one:

There is also a 4 slice CT scanner in the Emergency department that is operated by General Radiography technologists. There are a large number of research projects that are scanned at TGH as well as lung biopsies and pre/post transplant procedures.

The New Women's College Hospital is the newest addition to the corporate Medical Imaging family. Just last week, they said goodbye to their 4 slice scanner to welcome a new 64 slice scanner.

So, from 2.5 hours to 12 seconds, CT has come along way. On behalf of MSH/UHN/WCH's CT scan departments, we hope you enjoyed this brief overview of such a dynamic and technologically advanced section of healthcare!