Computed Tomography: Advantages and Disadvantages

This page explores the pros and cons of Computed Tomography (CT) scanning. We’ll cover the benefits and drawbacks of this valuable medical imaging technique.

Introduction

Traditional radiography creates a 2-dimensional image by superimposing images from successive layers of the body onto a single plane. This means the image of one layer can be obscured by the layers above and below it. Tomography was invented to overcome this limitation. In tomography, images of selected layers are recorded sharply, while others are intentionally blurred.

This technique involves some form of movement of the patient or equipment during the exposure. Tomography relies on synchronized movement of any two of the following three components: the X-ray tube, the film, and the patient, while the third component remains stationary.

What is Computed Tomography?

Computed tomography (CT) combines tomographic imaging with computer processing power. The CT scanner was invented by Godfrey Newbold Hounsfield in England.

A CT scan uses computer-processed combinations of many X-ray images taken from different angles to generate cross-sectional images.

A CT scanner consists of an X-ray tube that emits a finely collimated, fan-shaped X-ray beam directed through the patient to a series of scintillation detectors. These detectors measure the number of photons that exit the patient. The detectors form a continuous ring around the patient.

The X-ray tube moves in a circle within this fixed detector ring. The information collected is then used to construct a cross-sectional image of the patient.

The radiation transmitted through the patient’s body is sensed by an array of detectors. The patient is moved inside a chamber containing the X-ray tube and detectors on a trolley. Detectors can move in one axial direction, and this machine is called computerized axial tomography (CAT).

The computer’s role is to reconstruct images of the body layers from the output of the detectors. This arrangement eliminates the need for linear motion of the X-ray source and detectors, drastically reducing scanning time.

Benefits or Advantages of Computed Tomography

Here are the main advantages of CT scanning:

• Eliminates Superimposition: CT completely eliminates the superimposition of images from unwanted structures.
• High Contrast Resolution: It offers higher contrast resolution, allowing it to distinguish tissues with density differences of less than 1%.
• Multiplanar Imaging: Multiplanar reformatted imaging is possible due to multiple contiguous or single helical scans.
• More Detail Than Ultrasound: CT provides more detail compared to ultrasonography.
• Quicker and Cheaper Than MRI: It is often quicker, cheaper, and superior to MRI scanning in certain situations.
• Reduced Motion Artifacts: Motion artifacts are less of a concern in CT scans than in MRI scans.

Drawbacks or Disadvantages of Computed Tomography

Here are the limitations of CT scanning:

• Time Consuming: CT scans can sometimes be time-consuming.
• Expensive: It can be expensive for routine clinical use.
• Higher Radiation Exposure: The patient is exposed to higher levels of radiation compared to traditional X-rays.
• Equipment Cost and Accessibility: CT scanners are expensive and therefore not always accessible to everyone.
• Risk of Radiation and Contrast Agents: There’s a risk associated with ionizing radiation and iodinated contrast agents (used to enhance images).

A more recent variation of computed tomography is Cone Beam Computed Tomography (CBCT). CBCT uses a cone-shaped beam from an X-ray source, which produces a complete volume image in a single rotation – creating a volumetric dataset. This makes CBCT scanners quicker at providing results compared to traditional CT scanners.