BME 311 Exam 1

what is anatomy

study of the structure/morphology of living things

what is physiology

study of the functions of living organisms

what are the four levels of body organization

cell → tissue → organ → system

what does superior/cranial mean

toward the head

what does inferior/caudal mean

away from the head/lower

what does anterior/ventral mean

toward the front

what does posterior/dorsal mean

toward the back

what does medial mean

toward the body’s midline

what does lateral mean

away from the midline

proximal vs distal

proximal = closer to origin/trunk

distal = farther away

what does a coronal plane divide

anterior and posterior

what does a sagittal plane divide

right and left

what does an axial/transverse plane divide

upper and lower

what is a pixel

smallest represented 2D image area

what is a voxel

smallest represented 3D image volume

what is FOV

physical space represented by the whole image

what is a phantom

object with known characteristics used to test/calibrate an imaging system

what is an artifact

image feature that doesn’t represent actual anatomy/physiology

noise vs background

noise = random variation

background = systematic bias/offset

what is spatial resolution

ability to distinguish small objects/details

does a smaller spatial-resolution number mean better or worse resolution

better

what does PSF stand for

point spread function

does decreasing pixel size through resampling necessarily improve true resolution

no

what is partial-volume effect

one voxel contains multiple tissue/signal types and therefore gets an intermediate value

what is temporal resolution

how quickly an image/change can be acquired or detected

which has better temporal resolution: fMRI or EEg

EEG; milliseconds vs seconds

analog vs digital

analog = continuous

digital = discrete

how many values can N bits represent

2^N

how many values can 8 bits represent

256

how many values can 12 bits represent

4096

how many values can 16 bits represent

65,536

what does ADC stand for

analog-to-digital converter

what is sampling

measuring a continuous signal at discrete points

what is quantization

converting sampled amplitudes into finite digital levels

state the nyquist theorem

sample at least twice the highest signal frequency

a 100-Hz signal requires at least what sampling rate

200 Hz

sampling at 500 Hz gives what Nyquist frequence

250 Hz

what does smoothing do to noise

decreases it

what does smoothing do to spatial resolution

worsens it

what is coregistration

aligning two images in the same body region

what is windowing

mapping a selected range of image values across the display range to enhance contrast

equation relating wavelength and frequency

c=λν

approximate speed of light

3×10⁸ m/s

photon energy equation

E=hν=hc/λ

increasing frequency does what to photon energy

increases it

increasing wavelength does what to photon energy

decreases it

do photons have rest mass

no

1 keV equals how many eV

1000 eV

approximate size of atom

10^-10 m

approximate size of neutron

10^-14 m

maximum electrons in shell n

2n²

maximum K-shell electrons

2

maximum L-shell electrons

8

what is binding energy

energy required to remove an electron completely from an atom

excitation vs ionization

excitation moves electron to higher bound level; ionization removes it

approximate atomic ionization-energy scale

around 10 eV, depending on material

what happens during de-excitation

electrons fall into lower vacancies and release energy

two products of an electron cascade

characteristic x-rays or auger electrons

why are characteristic x-rays “characteristic”

their energies reflect fixed energy-level differences unique to the element

is rayleigh scattering elastic or inelastic

elastic

does rayleigh change photon energy

no

what does rayleigh change

photon direction

what energy range is rayleigh most relevant at

few keV/low x-ray energies

compton elastic or inelastic

inelastic

which electron does compton typically interact with

outer-shelll electron

does compton ionize the atom

yes

does the scattered compton photon lose energy

yes

approximate energy above which compton dominates in soft tissue

~30 keV

what does compton scatter do to image contrast

reduces it

what happens to the photon during photoelectric absorption

it completely disappears/is absorbed

which electron does photoelectric absorption eject

inner-shell electron

what follows photoelectric absorption

electron cascade → characteristic x-rays/auger electrons

photoelectron kinetic energy equation

photon energy - binding energy

approximate pair-production threshold

1022 keV = 1.02 MeV

what does pair production create

electron + positron

is pair production relevant to ordinary diagnostic x-ray imaging

no

what is attenuation

removal of photons from a beam by absorption and scattering

attenuation equation

N_out​=N_in​e^-μx

unit of linear attenuation coefficient μ

cm^-1

typical μ order for soft tissue

tenths of cm^-1 (~0.1-0.3 cm^-1)

what is HVL

thickness reducing beam intensity to half

HVL equation

HVL = 0.693/μ

how much remains after 3 HVL’s

1/8 = 12.5%

what is mean free path

average distance a photon travels before an interaction

MFP equation

1/μ

define photon fluence

number of photons per area

fluence units

photons/cm²

energy-fluence units

energy/area e.g. keV/cm²

absorbed dose equation

D=ΔE/Δm

absorbed-dose unit

gray (Gy)

what is 1 Gy

1 J/kg

equivalent-dose equation

H=Dw_R

equivalent-dose unit

sievert (Sv)

what does equivalent dose account for

biological effectiveness of different radiation types

effective-dose equation

E=∑w_T​H_T

what does effective dose account for

tissue sensitivity and whole-body risk

typical radiology procedure effective dose

roughly 1-10 mSv

dose occupational annual maximum

about 50 mSv/year

two primary components of an x-ray tube

cathode and anode inside a vacuum tube

what does the x-ray cathode do

produces electrons through thermionic emission