poi Flashcards
where are the x ray photons generated from
a complex X-ray tube, which is a type of cathode ray tube
why are The X-rays are then collimated
directed through lead-lined shutters to stop them from fanning out) to the appropriate area of the body.
what happens when the x ray goes through the body
As the X-rays pass through the body they are attenuated (reduced in energy) by the tissues.
what are the relative attenution if air fat water bone
▪ air attenuates X-rays a little;
▪ fat attenuates X-rays more than air but less than water; and
▪ bone attenuates X-rays the most
why is bone shown white
bone appears white on the film because this region of the film has been exposed to the least amount of X-rays. Air appears dark on the film because these regions were exposed to the greatest number of X-rays.
What is barium sulphate
Contrast agents
what is commonly added to barium and how
by either ingesting “fizzy” granules or directly instilling air into the body cavity, as in a barium enema. This is known as a double-contrast (air/barium) study.
which contrast agent is intervanoulsy added to teh vien /arteries and why (2)
Iodine is chosen because it has a relatively high atomic mass and so markedly attenuates X-rays, but also, importantly, it is naturally excreted via the urinary system
Subtraction angiography
subtract structures from the image, thus allowing for an accurate depiction of the blood vessels.
Ultrasound
very high frequency sound wave
The sound waves are then interpreted by a powerful computer, and a real-time image is produced on the display panel.
what is it generated by
piezoelectric materials
The sound waves are then interpreted by a powerful computer, and a real-time image is produced on the display panel.
what does Doppler ultrasound allow
determination of flow, its direction, and its velocity within a vessel
how
Sound waves bounce off moving structures and are returned. The degree of frequency shift determines whether the object is moving away from or toward the probe and the speed at which it is traveling
Computed tomography
A CT scanner obtains a series of images of the body (slices) in the axial plane. The patient lies on a bed, an X-ray tube passes around the body
Magnetic resonance imaging what it do
determine the structure of complex molecules
what does it depend on and why is it ideal
free protons in the hydrogen nuclei in molecules of water (H 2 O). Because water is present in almost all biological tissues,
how is mri carried out
The patient is placed in a strong magnetic field, which aligns the bar magnets. When a pulse of radio waves is passed through the patient the magnets are deflected, and as they return to their aligned position they emit small radio pulses. The strength and frequency of the emitted pulses and the time it takes for the protons to return to their pre-excited state produce a signal. These signals are analyzed by a powerful computer, and an image is created
two types of imaging sequences provide differences
image contrast
Most T1-weighted images show
dark fluid and bright fat
T2-weighted images demonstrate
a bright signal from fluid and an intermediate signal from fat
