3 Imaging and Nuclear Medicine Diagnostics

How imaging modalities differ

Imaging preparation varies with the specific study and facility. Follow the instructions from the ordering clinician and imaging team about fasting, fluids, bladder filling, and medications rather than assuming that one preparation rule applies to every exam.

Radiography and CT use ionizing radiation. MRI and ultrasound do not. CT uses x-rays to create cross-sectional images, MRI provides strong soft-tissue contrast, and nuclear medicine can provide functional information such as tracer uptake in tissues.

Radiography preparation and pregnancy

Routine radiographs usually require little preparation. The patient may be asked to remove jewelry or other objects that could interfere with the image. Most patients can resume normal activities afterward.

If pregnancy is possible, the patient should tell the clinician or technologist before a radiograph so the care team can consider the exam's benefits and risks and assess the safest appropriate imaging plan.

Preparing for contrast-enhanced CT

Before CT with intravenous contrast, the patient should report any previous reaction to iodinated contrast, kidney disease or impaired kidney function, current medications, and relevant allergies. Fasting instructions vary by exam, so patients should follow the instructions they receive rather than assume all CT scans require fasting.

A brief warm or flushed feeling, metallic taste, or temporary sensation of needing to urinate can occur with intravenous contrast. Throat swelling, difficulty breathing, or other severe symptoms require immediate attention from the imaging team.

MRI screening and safety

MRI uses a strong magnetic field and does not use ionizing radiation. A patient with an implanted medical device should disclose the exact device and bring its identification information. Some devices are safe only under specific conditions, while others may not be safe; the MRI team must screen and verify safety before scanning or entry into the MRI environment.

Patients should remove prohibited metal objects, use offered hearing protection, and tell the team about claustrophobia or concerns about remaining still.

Ultrasound preparation and findings

Ultrasound uses sound waves, not ionizing radiation. Preparation depends on the body area and exam: some studies may require fasting, while others may require a full bladder. For example, eating may affect a gallbladder study, and a pelvic study may require a full bladder.

Gallstones may appear as bright echoes with acoustic shadowing. The clinician interprets this finding in context.

Bone scan preparation and follow-up

For a nuclear medicine bone scan, patients should drink fluids as instructed after the injection. Fluids help clear radiotracer that does not bind to bone. Emptying the bladder before imaging, if instructed, can improve visualization of the pelvic bones.

Patients should discuss possible pregnancy or breastfeeding before the examination because radiotracer precautions may be needed. Follow any specific post-scan instructions from the nuclear medicine team.

PET/CT preparation

Before PET/CT, patients should follow the imaging team's fasting instructions and tell the team about diabetes and medications. Food and blood sugar or insulin levels can affect tracer distribution and scan quality, so patients should ask the team for individualized directions.

Increased tracer uptake can be seen in cancer but may also occur for other reasons. Increased uptake does not establish a diagnosis by itself.

Interpreting imaging findings

Imaging findings support clinical assessment but do not always establish a diagnosis on their own. A chest-radiograph opacity does not always prove pneumonia, and an area of increased tracer uptake is not diagnostic by itself. A bone scan hot spot can occur with several conditions, including fracture, infection, or cancer; uptake can also have other explanations on PET/CT. Findings must be interpreted with the patient's symptoms and other clinical information.

Responding to severe contrast symptoms

During a contrast-enhanced CT, throat swelling and difficulty breathing may indicate a severe contrast reaction. Notify the imaging team immediately and activate the facility's emergency response so the patient can receive immediate assessment and treatment. Airway symptoms are not routine, unlike mild warmth or a metallic taste that can occur during some contrast injections.