green app wrong Flashcards
TR: 500 TE: 10
T1 sequence. short short. (short TR <500 ms and short TE < 20 ms)
TR = 2000 TE = 70
T2 sequence. long long. TR > 2000, TE > 70
TR long, TE short
PD sequence
to correct for aliasing in Doppler what can you adjust
increase PRF, increase the scale, lower frequency transducer, gate closer to the transducer, doppler angle CLOSER to 90
what is the effect on chemical shift artifact if the receiver bandwidth is increased in MRI
DECREASE. TE, SNR, and mismapping artifacts all Decrease.
decreasing the doppler angle has what affect on aliasing?
it improves aliasing
how does using a lower frequency probe affect aliasing?
improves aliasing. size of the doppler shift is proportional to the fundamental imaging frequency. Using a lower f probe will result in a relatively smaller doppler shift –> decreased aliasing
common artifact encountered with a fluoroscopy system using flat panel detectors
persistence (ghosting) artifact.
reduction of image artifacts caused by eddy currents is achieved by using
actively shielded magnetic field gradient coils
which subatomic particle determines an atom’s chemical properties?
electron
what happens to contrast as latitude is increased
decrease
conventional radiographic film is exposed by what?
visible light
In CT, decreasing the FOV while keeping the matrix size constant will result in what?
decreased contrast resolution. Pixel size = FOV/matrix. Decreasing FOV –> decreased pixel size –> fewer photons per pixel –> increased noise –> decreased contrast resolution
what happens to beam intensity when mA is doubled?
beam intensity will double
decreasing the anode angle has what affect on focal spots?
actual focal spot size of the target NEVER changes. The EFFECTIVE focal spot size decreases –> decreased geometric blur.
Inherent filtration refers to attenuation of the xray beam by:
target material and xray tube window
when does max mA increase?
when the anode target rotational speed is increased. more heat is able to dissipate and the xray tube rating is increased.
how is the E of characteristic xrays produced by an xray tube compared to the k-shell binding E of the tungesten target?
characteristic xray E < k-shell binding E
if the wavelength of a photon is doubled, the E of the photon will…
decrease by a factor of 2. the E of a photon is directly proportion to its frequency and INDIRECTLY proportional to its wavelength.
applying Al filtration to the xray beam will do what to the image contrast
reduce. lower E photons filtered out –> increased average E (keV) –> decreased contrast.
100 samples per horizontal row that is 100 mm long. What is the limiting spatial resolution?
0.5 lp/mm. samples/row length (100/100 mm = 1 sample/mm). The limiting spatial resolution is 1/2 of the sampling frequency, or 0.5 lp/mm
