What is obesity?
“An increase in body weight by excessive accumulation of fat.”
Quantified by the Body Mass Index (BMI). A BMI of 30-39.9 is considered obese, and a BMI greater than 40 is considered morbidly obese.
Obesity and Radiography
There are numerous challenges when imaging morbidly obese patients, from practical considerations such as transportation, weight limits for imaging equipment and technical points of gaining diagnostic imaging studies. Ultrasound is the most affected modality
What is another way to reduce scatter in obese patients?
Use of a grid with a high grid ratio, such as 8:1 or 10:1 can reduce scatter and improve image quality
Grids also improve anatomic detail by reducing scatter and by increasing the signal-to-noise ratio (SNR)
Equipment Considerations
Tables in X-Ray, CT and MRI will have weight limits identified by the manufacturer (300-700lbs)
Be aware of these limits to not hurt the patient or yourself
Or damage the equipment
Transportation
Larger wheelchairs might be needed
Special beds/stretchers to move larger patients
Power lifts installed in DI and patient wards
Transfer and Movement Safety
Make sure the table can support patient weight
Always be sure adequate personnel are available to assist and that transfer tools such as sliders are available (It’s Your Move!)
Communicate each part of the transfer process to patient.
Explain positioning required for imaging procedure. Provide support and assistance to maximize patient comfort and security.
Positioning and Landmarks
- Ensure the patient is positioned accurately to the centre of the table
- Realize that the bony skeleton and most organs have not changed position and that the organs are not larger
- Most palpable landmarks are not accessible in the morbidly obese.
- Most fat accumulates around the trunk.
- Never prod patient unnecessarily.
- Most positioning landmarks on obese patients will be reference points in the mid-sagittal plane of the patient.
- The jugular notch may be the only landmark available for palpation.
Land marks for positioning
- Locate jugular notch
- Pubic symphysis can be located by using the following measurements from the jugular notch based on patient height:
- <5 feet: 21 inches or 53 cm
- 5 to 6 feet: 22 inches or 56 cm
- >6 feet: 24 inches or 61 cm
Image receptor size and collimation
- Using proper IR sizes and standard collimation practices will reduce scatter on the image
- For colon and other abdominal images, it may be necessary to take multiple pictures on quadrants of the body, using smaller collimation settings
- The collimator should never be set larger than the size of the IR
Exposure factor considerations
- The most important adjustment to be made is increasing your kVp to increase the penetration of the beam, but ensure your mA and time are moderate! The mA for obese patient X-rays may be higher than 250-320 mA
- Selection of a larger focal spot for all but distal limbs.
- Maintain a special exposure technique chart for obese patient projections for future reference and lowering repeats.
Mobile Exams on Obese Patients
- May be restricted to chest and limbs only as machine’s exposure factors need to be high enough to penetrate the patient.
- Using a grid will increase contrast resolution.
In Summary: Technical considerations for working effectively with obese patients
- Warm up X-ray tube before making any exposures.
- Use lower mA settings (< 320).
- Use higher kVp settings.
- Do no make repeated exposures near X-ray tube loading limit.
- Use the large focal spot for all but distal limbs.
- Do not use APR systems to determine exposure technique.
- When using AEC systems, ensure kVp is high enough and mA is moderate.
- Collimate to the size of IR or smaller.
- With DR, collimate to suggested field size for the projection.
- Never collimate to the maximum 17 x 17 inch 35 x 35 cm size of the flat panel DR detector.
- Maintain special exposure technique chart for obese patient projections.
- Stand at right angles (90 degrees) to the central ray when holding an obese patient.
