Sometimes imaging parameters can be adjusted to obtain better quality images for large patients, albeit at the cost of increased radiation dose. This can result in motion artifact as exposure time increases, also decreasing the diagnostic value of the imaging study. Increased thickness also increases the amount of time it takes for the x-ray to penetrate the body. Increased attenuation causes images to look “noisy” (i.e., more grainy) in appearance, which may decrease the diagnostic value of the imaging study. Increased tissue thickness results in attenuation of x-rays.
Patient size can impact CT image quality and result in imaging artifacts. 2 Impacts on Image Quality & Radiation Dose Beam hardening artifact and decreased image quality result from the improper positioning (c, d). 1Īxial and coronal CT images from a patient scanned positioned with their arms overhead (a,b) versus down by their side (c, d). Images demonstrating how the table narrows gantry size, most notably in the vertical dimension. This positioning may have variable effects on a patient’s ability to fit into the scanner. Ideally, CT scans are performed with patients’ arms in an outstretched position over their heads, as this reduces imaging artifacts. Patients should be able to lie flat for the duration of the exam.
Most CT scans are performed with the patient in a supine position. It is important to note that the scanner’s vertical diameter is further constrained by the table (as demonstrated by the image below) and must be taken into consideration when determining if a patient will fit into the scanner. The patient, or body part of interest, must fit within the CT gantry (doughnut-shaped opening) in both the vertical and horizontal dimensions in order for the scan to occur. This will obviate the need for transfer of inpatients between Parnassus and Mission Bay.įor additional questions about MRI scanner diameter and weight limits, please contact:ĬT scanners have both weight and diameter limits. ***MRI with 550 lbs weight limit and 70 cm max diameter will be installed at Parnassus campus early 2022. **There is a protocol for transferring Parnassus inpatients to Mission Bay to obtain imaging when necessary and appropriate. Padding and coils may decrease the maximum patient diameter by up to 5 cm. Maximum diameter listed does not account for padding and coils necessary for safe and effective imaging. *Diameter is often the limiting factor for MRI. If you are caring for a patient whose size might preclude successful imaging and you would like to discuss this with our UCSF radiology team, please use the contact information provided below. The final evaluation and decision on whether it is safe to proceed with imaging or imaging-guided intervention will be made by the radiology imaging modality managers. These are described in greater detail in the sections dedicated to each imaging modality. Each imaging modality has additional considerations that may preclude successful imaging, even when patients technically meet the manufacturers’ specified limits. different CT scanner models have different specifications). The limits provided below represent the maximum weight/diameter capacitance of a single piece of equipment with the greatest capacity at each UCSF Health imaging site these limits are not applicable across modalities (MRI vs. This website aims to provide information on the size and weight limitations for UCSF imaging modalities. It is essential to operate imaging equipment within limits not only to ensure high quality imaging, but also to avoid patient harm, staff injury, and equipment malfunction. CT, MRI) and even between equipment within each modality.
These limitations, including patient weight and diameter, vary between imaging modalities (e.g. Important patient size limitations must be considered when obtaining diagnostic imaging and performing image-guided interventions.
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