Flashcards in Introduction to Imaging Deck (22):
Define what an x-ray is
An electromagnetic packet of energy with an extremely short wavelength between 0.1 and 10 nanometres.
Describe the process of x-ray production and image capture
Inside an x-ray machine, an electron gun (cathode) fires high energy electrons at a heavy atom material (tungsten of anode). The collision of the electrons with the heavy materials creates “braking radiation” in the form of x rays.
These x-rays are then directed at the target being photographed. Some rays are absorbed by bone and others pass through and hit the imaging film. The emulsion contains silver halide which forms clumps on the film upon exposure.
Explain why different anatomical structures have different appearances on an x-ray image
Different types of tissues absorb different amounts of radiation. In order of least absorption to most, it goes air, fat, muscle then bone. Depending on how much radiation is absorbed, the image produced will be different.
Describe the basic principles of ultrasound
This works by firing sonic waves a frequencies between 2 and 18 megahertz into the patient in order to scan soft tissues such as muscles, tendons and also to monitor embryonic development. The reflected sonic waves are picked up by the probe and relayed to the machine.
Explain the strengths and weaknesses of ultrasound scanning
• No long term side effects or discomfort
• Trouble penetrating bone
• Operator dependent
• Trouble scanning through gas pockets
Describe the basic principles of CT scanning
CT scanning involves taking a series of 2 dimensional x-ray images around a single axis of rotation to create a 3 dimensional image of the patient.
Explain the strengths and weaknesses of CT imaging
• Resulting scan can be viewed in the saggital, axial or coronal planes as necessary.
• Due to high resolution, it is possibly to differentiate between tissues of similar density.
• Some patients may have reactions to contrast dye
• CT scans can increase chances of contracting cancer
Describe the basic principles of fluoroscopy imaging
Fluoroscopy is an imaging technique used to obtain real time moving images of the internal structures of a patient. In its simplest form, a fluoroscope is an x ray source and a fluorescent screen between which the patient is placed.
Explain the strengths and weaknesses of fluoroscopy
• Moving images obtained using special camera
• Patient is exposed to ionising radiation as with all x rays
Describe the scientific basis of the use of iodinated contrast media.
Iodinated contrast is a form of IV radiocontrast containing iodine, which enhances the visibility of vascular structures and organs during radiographic procedures.
Describe the scientific basis of the hazards of the use of ionized contrast media, and can be done to prevent any damage
The iodine however is nephrotoxic and can result in kidney failure. Extra fluids should always be administered after its use to “flush” the system.
Describe methods of minimising radiation exposure
Reduce time of exposure
Why is imaging used?
When physical exam is unreliable
Better understanding of underlying issue
Roadmap for procedures and treatments
Can be used to assess response
Describe the X-ray tube design
X-rays can be generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. The high velocity electrons collide with a metal target, the anode, creating the X-rays. In medical X-ray tubes the target is usually tungsten, but sometimes molybdenum is used for more specialized applications, such as when softer X-rays are needed as in mammography.
What is attenuation and what factors influence it?
Attenuation is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption or by deflection (scatter) of photons from the beam and can be affected by different factors such as:
o Beam energy
o Increases with Z (atomic number) of the absorber
o Increases with density
o Increases with thickness
Explain the strengths and weaknesses of x-ray imaging
o Less radiation exposure than CT
o Fast and efficient
o Only 2D
o Some inability to accurately distinguish between different densities of some tissues, making it difficult to visualise anatomy
o Exposure to radiation
Describe the basic principles of barium studies and what they're still used for.
A radio-opaque contrast agent is used for outlining the gastro-intestinal tract. The high atomic number of barium absorbs more x-ray photons than surrounding tissues, giving a brighter image. Rarely used now, though are useful for:
• Swallow and meal - oesophagus, stomach and duodenum
• Small bowel study - small bowel
• Enema - large bowel
Describe the possible complications of barium use
• Bowel disturbance (very common)
• Colonic perforation at enema
– Very rare (<1:25,000)
– More common if underlying abnormality (e.g. severe inflammation in IBD)
• Possibility of leak
• Barium peritonitis occurs 50% within 7 days of full thickness biopsy
Name the three radiation types and describe their levels of penetration
• There are three types of nuclear radiation: alpha, beta and gamma. Alpha is the least penetrating, while gamma is the most penetrating
What is the units used to describe the absorption of radiation by the human body?
Define ionising radiation and its risk
A particle or a wave with sufficient energy to ionise a neutral atom or molecule and leave them with a charge. Process of ionisation can lead to the disruption of chemical bonds within living tissue, damaging tissues and possibly resulting in the development of cancer