A Computed Tomography (CT) scan is a medical imaging procedure that uses a series of X-ray measurements from different angles to produce detailed, cross-sectional images of the body. For a successful scan, a patient’s physical characteristics are taken into account. Both height and weight can influence the feasibility and outcome of a CT examination.
CT Scanner Physical Limitations
CT scanners have mechanical and structural constraints that can limit which patients can be accommodated. The first factor is the weight capacity of the motorized table the patient lies on, as its motor and structure can only support a certain amount of weight. Most standard CT scanner tables have a weight limit of 450 to 500 pounds. Exceeding this limit can prevent the table from moving correctly, making a scan impossible.
The second physical limitation is the diameter of the gantry, the ring-shaped opening, or bore, that the patient must pass through. Standard CT scanners typically have a bore diameter of about 70 centimeters, or around 27 inches. While a patient’s height is not a direct issue, their body width is. If a patient is too broad, particularly at the shoulders, they may not be able to physically fit through the opening, regardless of their weight.
How Body Size Affects Image Quality
Beyond the ability to fit into the machine, a patient’s body size directly impacts the quality of the images produced. CT imaging relies on X-ray beams passing through the body to a detector on the opposite side. Increased body tissue, particularly adipose tissue, can absorb and scatter these X-ray photons before they reach the detector. This can lead to photon starvation, where an insufficient number of photons are captured to create a clear image.
When the X-ray signal is weakened, the resulting images can suffer from “image noise,” making the scan appear grainy or blurry. For a radiologist, this noise can obscure fine details, making it difficult to distinguish between different types of tissues or identify abnormalities. To counteract this, technicians may increase the X-ray tube voltage, but there are limits to this adjustment, and a diagnostic-quality image may not be obtainable.
Alternatives for Bariatric Patients
When a patient exceeds the physical or imaging limitations of a standard CT scanner, alternatives are available. Many imaging centers now operate wide-bore CT scanners designed for larger individuals. These machines feature larger gantry openings, often 78 to 80 centimeters, and have reinforced tables with higher weight capacities, sometimes over 600 pounds.
If a CT scan is not feasible, other imaging methods may be considered. Magnetic Resonance Imaging (MRI) is one option and also comes in wide-bore configurations; it uses magnetic fields instead of X-rays and is better for viewing soft tissues. Ultrasound is another modality that does not have strict weight limitations, but its ability to visualize deep structures can be limited by body size. The choice of an alternative depends on the specific medical question the healthcare provider is trying to answer.