Everything Flashcards
(31 cards)
At what kV does compton scatter predominant?
70 kVp
Photon energy of common radiophaemaceuticals
Tc99m - 140keV
Iodine 131 - 364 gamma keV
Fluorine18 - 511keV gamma
Gallium68 - 511keV gamma
Half life of common radiopharmaeuticals
Tc99m - 6 hours
Iodine 131 - 6 days
Fluorine18 - 2 hours
Gallium68 - 1 hour
What is the equation that relates dose to radius in fluoroscopy
dose = r^2 (therefore also diameter squared)
Noise (propotional) equation
Noise = 1/root(photons)
SNR equation
SNR = N/root(N)
CNR equation
CNR = (pixel value of lesion - pixel value background)/root(N)
US: equation relating speed of sound (C) to wavelength and frequency
How does speed of sound related to bulk modulus and density?
c = wavelength x frequency
c = root (B/p) - the stiffer the medium (higher B), the faster. The lower the density, the faster
US: how is pressure (wave amplitude) related to power (W)?
Power (W) is proportional to pressure^2
US: how do we calculate intensity?
Intensity is proportional to power(W)/area(cm2)
US: what is dB?
Relative intensity
dB = 10log Intensity2/Intensity1
Change in 3 of dB is half/double
Change in 10 of dB is a tenfold change eg. 10dB 1/100, 20dB 1/1000
US: how do we calculate how much is reflected back?
R=([Z2-Z1]/[Z2+Z1])^2
Reflection = difference between acoustic impedance / sum of acoustic impendence
US: what is specular reflection?
what is refraction and how does the angle change with speed of sound changes?
incidence angle = reflection angle (on smooth surfaces)
refraction occurs when the sound beam penetrates the interface
- slowing of speed = decrease in transmittance angle
- increasing of speed = increase in transmittance angle
US: what is the soft tissue attenuation coefficient?
Soft tissue attenuation coefficient ~0.5(dB/cm)/MHz
therefore Soft tissue attenuation = frequency x 0.5(dB/cm)/MHz
US: what is the formula and SI unit of acoustic impedance (Z)?
Z = density (p) x speed of sound (c)
SI unit = kg/m2.s or rayls
US: what is the Q factor? How does it relate to dampening blocks?
Q factor describes purity/quality of beam
Higher Q - narrow bandwidth, longer spatial pulse frequency (SPF), less dampening
Lower Q - wide bandwidth, shorter SPF, more dampening
US: how does diameter and frequency affect the distance of near field and divergence of far field in the US beam?
Increased frequency and increased transducer diameter results in:
- increase of near field distance
- decrease of divergence angle
what is the equation linking acoustic impedance (Z), speed of sound (c) and density (p)?
Z = c x p
How would you define MTF?
MTF (mean transfer function) is an imaging systems ability to transfer an input signal to an output signal at a given spatial frequency. It is used to measure spatial resolution, with 1 or 100% meaning perfect signal transfer and 0 meaning complete loss of information
What is bright and dark in T1?
Fat - bright (short T1)
Water, bone - dark (long T1)
What is the definition of T1
The time at which longitudinal magnetization is 63% of its final value
What is the definition of T2
12 representing the time at which the signal has decayed to 37% of its original value of transverse magnetization (63% of it has decayed)
How do you define T2*
T2* = tissue spin interactions + field inhomogeneity
(random interactions + fixed cause)
What is the rough duration of TR, TE for T1w images in SES?
Medium TR - 400-600ms to catch the middle of the Mz regrow
Short TE - 3-10ms to minimise effects of Mxy
