Introduction to imaging techniques Flashcards
What is the difference between a radiologist and a radiographer
Radiologist: doctor specialising in imaging interpretation
Radiographer: technician who takes images
When were X-Rays first used for imaging
1895.
When was CT scanning first introduced into clinical practice
1971.
When was MRI introduced into clinical practice
1983.
What is radiology
Diagnostic Imaging
Interventional Radiology
Do not confuse with radiotherapy
Describe the importance of radiology in clinical practice
Imaging is necessary in most clinical specialities to diagnose pathological changes to tissues. It is paramount to appreciate what is normal and what is abnormal. An appreciation of how the image is obtained, what the normal variations are, and technical considerations is necessary to obtain a radiological diagnosis.
Distinguish between ionising and non-ionising radiation
Ionising Radiation
X-ray & computed tomography (CT)
Nuclear Medicine
No ionising radiation
Ultrasound
Magnetic Resonance Imaging (MRI)
What are the sources of background radiation
Radon gas from the ground- majority Buildings and the ground Artificial rays- medical sources represent 14% of background radiation. Cosmic Rays Food and Drink.
What is the problem with ionising radiation
relationship with development of cancer years after exposure; the younger the patient, the higher the mortality and incidence of cancer in later life (between 0 and 10- greater risk of cancer later in life).
Describe X-rays
X-rays are photons and are generated from a complex X-ray tube, which is a type of cathode ray tube. The X-rays are then collimated (directed through lead-lined shutters to stop them from fanning out) to the appropriate area, as determined by the radiographic technician. As the X-rays pass through the body they are attenuated (reduction in energy) by the tissues. The X-rays that pass through the tissues interact with the photographic film.
Describe the passage of X-rays through air and fat
Low density tissues
Appear black on X-ray
Describe the passage of X-rays through soft tissue
50% X-rays pass through GREY
Soft tissue
Describe the passage of X-rays through bone
Few X-rays pass through WHITE
Bone
What do different attenuations of the X-rays result in
These differences in attenuation result in differences in the level of exposure of the film.
More exposure=black
Less exposure=white
Most of the X-rays are absorbed by bone- less reach the film- which is why it appears white.
Describe the contrast between different body parts seen in X-rays
Air- Black Fat- Fairly Black Soft tissue- gray Bone, calcium- white Metal- really white.
What can be seen on a chest radiograph
Lungs full of air so are distinguishable from tissues, but cannot distinguish between heart muscle, pericardium and blood in the heart due to similar densities
Fat has a different density so can be distinguished from tissue (muscle)
Describe the abdominal radiograph
left-sided kidney may appear white due to calcium deposits
Usually taken in AP supine position
Erect PA when small bowel obstruction is suspected.
What is inherent tissue contrast improved by
Contrast agent enhances the differences between tissues of similar densities Commonly used contrast agents: Barium Iodine Various ways they are introduced Swallowed Via rectum Into artery or vein
Contrast agents appear white on X-rays
Describe the use of barium sulfate and iodine
Barium sulfate- insoluble salt, nontoxic, high-density agent- useful for examining the GI tract.
Iodine- directly in arteries or veins- high atomic mass (so markedly absorbs X-rays well)- excreted naturally via the urinary system- and so can be used in intravenous urography
Describe the safety of intra-arterial and intra-venous contrast agents
Extremely safe and well tolerated by most patients Some patients (rare) have an anaphylactic reaction to these injections and so the appropriate precautions must be taken.
Describe the importance of CT scans
Can appreciate differences between soft tissues (e.g water) unlike X-rays.
Describe how images are obtained in CT scans
The patient lies on a bed
An X ray tube passes around the body and a series of images are obtained
A computer carries out a complex transformation of the multitude of images to perform a cross-sectional map of tissue density.
Describe the appearance of different entities on CT scans
Organs are different shade of grey depending on water content; skin is white, fat is black and air is black
Describe CT windows
Enhance the CT scan to look at different areas (soft tissue, bone, lungs)- set digital imaging.
changes interpretation to expose different details based on focussing on different density depending on structure to image
