What is a CT Scanner?

In this article we will describe the inner workings of a computerized tomography scanner (CT Scanner), sometimes called computerized axial tomography or computer aided tomography (CAT scanner), and the types of exams that it can perform.  

The origins of Computer Aided Tomography, who invented the first CT scanner?

The first CT scanner was invented by British engineer Godfrey Hounsfield of EMI laboratories. In 1971, Houndsfield along with Dr. Ambrose scanned a female patient that suffered from a brain tumor in Atkinson’s Morley Hospital. That first scan took days to image the tumor.

By 1973, the United States installed its first unit and by 1980, three million CT exams had been recorded.

How does a CT scanner work?

A basic CT machine consist of a gantry, a moveable table, and a control room. Inside the gantry contains the x-ray tube and an array of detectors. The 3-D rendered image is accomplished by rotating the x-ray tube in an ‘arc’ around the patient while their body moves through the gantry, which is the circular structure in the middle of the CT scanner.

The x-ray tube uses a fan shaped beam to take 2D images of the coronal, sagittal, and cross-section planes of the body. One revolution equals a slice and produces a 2D image of that slice or plane. Slices are collected in a computer and the scanning process continued until the desired number of slices are achieved.

Then, advance computer algorithms are used to reconstruct 3D images of those planes or slices. Slice thicknesses range from 1mm to 4 mm and are stacked to see a 3D image.

The fully rendered 3D images reveal detailed images of bones, soft tissues, and organs.

Here’s how CT units acquires images 

Image reconstruction relies on different tissue densities that attenuate the x-ray beam at different energies. For example, x-rays will not penetrate bone or thicker body parts as easily as soft tissues such as muscles, ligaments, and cartilage.

Thicker body parts, such as bones will be lighter in value and softer tissues such as muscles, will be darker. Those value differences are assigned numeric units which are fed into a computer to reconstruct a 3D digitalized image of the body part. A contrast dye can sometimes be used to show certain structures more clearly.

CT images reveal details of bone, muscle, cartilage and other soft tissues and organs. The scan can determine the size and shape of the lesion or fracture deep inside the body. CT 3D images make it easier for physicians to find the location of the problem by allowing them to rotate the image in space or view slices in succession.