Biophysics Flashcards
How to interpret DEXA scan results?
T score -1 or more normal
T score -1 to -2.5 osteopenia
T score less than -2.5 osteoporosis
What do vertical small boxes represent on ECG?
0.1 mV
What do vertical large boxes represent on ECG?
0.5 mV
TVUSS frequency?
7.5 MHz
How to determine acoustic impedance?
Density of tissue x velocity of US in that particular tissue
What is reflection in US?
Occurs at interfaces between tissues with different characteristics, determined by acoustic impedance (more AI = more reflection)
What is scatter in US?
Occurs when US interacts with structures that are similar in size or small than wavelength, increases with frequency
What is absorption in US?
Conversion of mechanical energy into heat, increases with frequency
What determines frequency in US?
Thickness of piezoelectric crystal
What is spatial resolution US?
Minimum distance between two reflectors or scattering surfaces necessary to be able to distinguish two separate echo signals
Depends on axial resolution, lateral resolution, and slice thickness
What determines axial resolution?
Pulse length, which is shorter at higher frequencies so high frequency = better axial resolution
What determines lateral resolution?
Beam width, dependant on beam focusing
What determines slice thickness?
Thickness of transducer
What factors influence penetration?
Absorption and scatter
As both increase with increasing frequency, lower frequency = better penetration (but poorer resolution)
Ideal set up for best quality image?
Fast frame rate, high line density, large field of view (but something has to be compromised)
What is Doppler frequency shift?
Difference in frequency between returning echo and transmitted ultrasound wave
Mechanism assessing blood flow on US?
Combined B-mode real-time grey-scale imaging with pulsed-wave Doppler and colour flow imaging (colour flow scanner)
What is cavitation in US?
Gas-filled cavities in tissues can oscillate or collapse under pressur eof US beam –> shear forces, high pressures/temperatures, or free radical production
Physiological ECG changes in pregnancy?
LAD, TWI and Q waves in III and aVF
