Module 1: Principles of medical imaging (P1)

What is electromagnetic radiation?

Electromagnetic radiation travels in waves and is carried by photons produced by the movement of electrons within atoms.

How are x-rays produced?

X-rays are produced in a glass vacuum tube where a cathode and an anode are present. Electrical current heats the cathode filament, causing electrons to be propelled towards the anode, which rotates to prevent overheating and produces x-ray photons.

What do denser structures appear as on an x-ray?

Denser structures such as bone, metal, or contrast medium absorb more photons and EMR, appearing as white on an x-ray, which gives a radiopaque appearance.

What do low-density structures appear as on an x-ray?

Low-density structures absorb minimal photons and EMR, appearing as black on an x-ray, which gives a radiolucent appearance.

What is the significance of penetration in radiographs?

Penetration refers to how well photons have penetrated the patient's body.

What is an under-penetrated x-ray?

If an x-ray is under-penetrated not enough photons (aka EMR) have reached the detector- appear as an excess of white.

What is over-penetrated x-ray?

If an x-ray is over-penetrated an excess of photons (aka EMR) have reached the detector- appear as an excess of black on the film.

How does distance affect magnification in x-ray imaging?

The further a structure is from the x-ray film and closer to the photon beam, the more it will be magnified on the final image, potentially leading to fuzzy images.

What is the orientation of patient images in x-ray viewing?

When viewing an x-ray, the image is mirror imaged; the patient's left side is on the viewer's right side.

What is orientation of a posterior-anterior x-ray?

Patient's POSTERIOR side is closer to the x-ray beam and their ANTERIOR side is closer to the detector

What is orientation of a anterior-posterior x-ray?

Patient's ANTERIOR side is closer to the x-ray beam and their POSTERIOR side is closer to the detector

What are the risks associated with x-ray imaging?

X-ray imaging uses ionizing radiation, which can cause DNA damage and increase the risk of developing cancer.

What influences the risks associated wtih x-ray imaging?

Influenced by radiation dose, patient's age, sex, and body region exposed (organs with rapidly dividing are more radiosensitive).

Why is x-ray exposure discouraged for pregnant women?

Exposing pregnant women to radiation is discouraged due to the increased risk of birth defects and cancer later in life, depending on gestational age and exposure amount.

How to minimise x-ray exposure in pregnant women?

Cover areas not being imaged with a lead apron to block scattered radiation and avoid abdominal x-rays where possible.

What are some considerations with children and radiation?

There is small but statistically significant risk of cancer over a lifetime in children who recieve excessive exposure to radiation. Sedation to remain still and caregiver presence.

What are the two general phenomena measured in radiation?

Radiation activity, which is the amount of photons emitted per second by a source, and radiation exposure, which is expressed in various ways.

What is a computer tomography (CT) scan?

A CT scan involves taking a series of individual images that are compiled electronically to create a 3D image of the body, rotating 360 degrees around the patient.

How can you compare CT scans to x-ray?

CT scans provides a more comprehensive view in comparison to conventional x-rays. They also have higher dose of radiation that regular x-rays.

What is the role of contrast medium in imaging?

Contrast medium enhances the visibility of specific organs, blood vessels, or tissues in various imaging modalities, including x-ray, CT, MRI, and ultrasound.

What are some types of contrast medium?

Barium sulfate

Iodine based

Gadolinium

Gas

What is barium sulfate used for?

Barium sulfate is an orally administered contrast medium used in x-ray or CT imaging of the gastrointestinal tract, being insoluble in water to minimize absorption.

What are the contraindications for barium sulfate?

Suspected GI perforation

Large volume aspiration risk

Prior allergic reaction

Conditions which place patients at increased risk of adverse events (allergy, asthma, CF, dehydration)

What is iodine based CM used for?

Injectable medium commonly used in x-ray and CT imaging.

What are the absolute contraindications for iodine contrast medium?

Previous severe reaction.

What are the relative contraindications for iodine contrast medium?

Previous mild reaction

Renal impairment

Diabetes patients on metformin

Myasthenia gravis

What considerations are there for patients with renal impairment when using iodine contrast?

Patients with renal impairment may require IV fluids or dialysis, and creatinine and eGFR should be assessed prior to using iodine contrast medium.

When should you not use contrast medium?

Suspected trauma or pathology associated with fibrosis and calcification.

When is contrast medium not indicated?

Head/spine.extremity trauma

Acute stroke workup

Diffuse lung disease

Kidney stones/coronary calcium stones

When is contrast medium indicated?

Contrast medium is indicated for inflammatory vascular pathologies, suspected malignancies, and conditions like diverticulitis or pulmonary embolism.