- Barium sulphate is a radio-opaque contrast (impenetrable to X-rays)
- used for outlining the gastro-intestinal tract.
high atomic number of barium absorbs more x-ray photons than surrounding tissues so it appears white
Why/when are medical imaging used
- Determine Initial diagnosis and staging of disease
- Monitoring response to treatment
- Evaluation of residual mass after treatment
- Recognition of complications of treatment
- When there is concern for disease relapse
How are Barium enema done
- Patient in left lateral position with tube in rectum
- Barium runs into descending colon to splenic flexure
- Turn patient onto right side and let barium run out
Inflate bowel with air
- Column of contrast pushed forward to caecum by air
- Image in different planes
Note on patient preparation:
- Barium meal and follow-through - fast for 4-6 hours.
- Barium enema - low residue diet for 48 hours and bowel cleansing with Picolax.
Describe Computed tomography
- In this form of computer-assisted radiography, an x-ray beam traces an arc at multiple angles around a section of the body. The resulting transverse section of the body, called a CT scan, is shown on a video monitor.
- Visualizes soft tissues and organs with much more detail than conventional radiographs. Differing tissue densities show up as various shades of gray. Multiple scans can be assembled to build 3D views of structures
- Whole-body CT scanning typically targets the torso and appears to provide the most benefit in screening for lung cancers, coronary artery disease, and kidney cancers.
Attenuation values of voxels are expressed as a CT number which relates the attenuation value to that of water.
- Ranges from +3000 (bone) to -1000 (air)
CT contrast agents
Oral - dilute iodine based contrast (gastrografin) can be given to outline the gastrointestinal tract (rarely used now)
Intravenous - iodine based contrast (Omnipaque) injected into the veins to demonstrate blood vessels or the vascularity of different tissues
- Occasionally allergic and anaphylactic reactions with IV contrast occur.
Diagnosis and staging of image
Position of tumour
Depth of penetration of tumour
Relationship to adjacent structures
- Involvement of regional lymph nodes
- Presence of distant metastases
ALARA Principle for minimizing radiation exposure
- As Low As Reasonably Achievable
- Ensure whether examination is necessary
- Adequate clinical information is essential for appropriate protocol
Avoid repeat examinations
Descibe Magnetic Resonance Imaging
- The body is exposed to a high-energy magnetic field, which causes protons in body fluids and tissues to arrange themselves in relation to the field. Then a pulse of radio waves “reads” these ion patterns, and a color-coded image is assembled on a video monitor. The result is a 2D/3D blueprint of cellular chemistry.
differentiating between normal and abnormal tissues.
- Used to detect tumors and artery-clogging fatty plaques;
- reveal brain abnormalities;
- measure bloodflow
- detect a variety of musculoskeletal, liver, and kidney disorders.
- Bones aren't seen clearly
- Can't be used on patients with metal in their bodies e.g patients with pacemakers, aneurysm clips
- Claustrophobic and noisy
- motion artefact
MRI contrast agents
Gadolinium DTPA is an intravenous contrast medium which causes changes in local magnetic field and so alters the tissue signal.
- Also Vascular lesions and some tumours can be more easily seen.
WHO principles of screening
- The condition should be an important health problem.
- There should be a latent stage of the disease.
- There should be a test or examination for the condition.
- The test should be acceptable to the population
- There should be a treatment for the condition.
- Facilities for diagnosis and treatment should be available.
- Test should detect disease at an early stage, where treatment can alter outcome
- Test should be harmless
- Test should have high sensitivity and specificity
- Benefit must outweigh cost