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MEDICAL BIOPHYSICS > IMAGING METHODS > Flashcards

IMAGING METHODS Flashcards

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USMLE® Step 1 flashcards
1
Q

WHAT IS THE WAVELENGTH OF THE VISIBLE SPECTRUM?

A

390-750nm

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2
Q

VISIBLE SPECTRUM BASED IMAGING METHODS

A

-optical methods to display a structure in the visible spectrum
-large wavelength means maximum resolution and magnification
-unable to visualize structures inside the body
-used in pathology and biopsies

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3
Q

ULTRASOUND

A

-use non-audible mechanical waves
-1 to 20 MHz
-reflected waves processed to produce an image
-used for baby

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4
Q

X-RAY

A

-xrays of different energy
-detectors record xray and produced an image
-2D or 3
-electromagnetic radiation in wavelength range of 0.01-10nm and energies of 100eV to 100keV
-formed from high velocity electrons colliding with a metal target, the anode usually tungsten
-only 1% of energy becomes an xray and the rest is lost as heat
-lungs, trapped gases and bone show up well in radiographs

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5
Q

ULTRASONOGRAPHY / SONO

A

-sound waves of compression and decompression of the transmitting medium traveling at a fixed velocity
-longitudinal or transverse waves
-audible sound frequencies are below 15,000 - 20,000MHz
-low frequencies bend around a corner, higher frequencies travel in straight lines
-generated by piezoelectric crystals
-emitted pulses reflected and sampled at multiple time intervals corresponding to multiple depths
-reflecting structures usually termed scatters

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6
Q

ACOUSTIC IMPEDANCE

A

speed of sound in material X density

Z = c x D

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7
Q

REFLECTION COEFFICIENT

A

ratio of the amplitude of the reflected pulse and the incident
-dependent on acoustic impedance

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8
Q

TRANSMISSION COEFFICIENT

A

ratio of the amplitude of the incident pulse and the transmitted pulse
-dependent on acoustic impedance

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9
Q

TIME LAG

A

time it takes for the sound to travel to the scatterer and back

r = c(pie) / 2

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10
Q

REFLECTED SIGNAL OF ULTRASOUND

A MODE

A

-amplitude mode
-simplest type of ultrasound
-signal transducer scans a line through the body with the echoes plotted on a screen as a function of depth
-specific tumors

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11
Q

REFLECTED SIGNAL OF ULTRASOUND

B MODE

A

-2D mode / brightness mode
-linear array of transducers simultaneously scans a plane through the body that can be viewed as 2D images on a screen

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12
Q

REFLECTED SIGNAL OF ULTRASOUND

M MODE

A

-motion model ultrasound
-pules emitted in quick succession
-A or B image taken each time
-records a video
-used to determine velocity of organs

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13
Q

ATTENUATION

A

-gradual loss of intensity
-ultrasound waves attenuated due to reflection and scattering
-10% of total energy loss
-attenuated mainly due to absorption in the tissue which generates heat
-minor amounts attenuated due to diffusion

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14
Q

WHAT IS ABSORPTION THE LIMITING FACTOR FOR?

A

the depth of the penetration of the beam

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15
Q

WHAT IS ABSORPTION DEPENDENT ON?

A

-density of tissue (higher density higher absorption)
-frequency of beam (higher the frequency the more absorption)

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16
Q

WHAT IS A WAY IN WHICH ATTENUATION CAN BE BYPASSED?

A

harmonic signaling
-> beam is transmitted at a certain frequency and the received signal is analyzed at twice that frequency
-> this increases the signal-noise ratio of the reflected signal without a loss of resolution

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17
Q

PENETRATION FOR GOOD IMAGING

A

10-20cm at 3.5MHz
5-10cm at 5MHz
2-5cm at 7.5MHz
1-4cm at 10MHz

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18
Q

HOW CAN THE VELOCITY OF BLOOD OR TISSUE BE MEASURED?

A

the doppler shift of the reflected ultrasound

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19
Q

WHAT IS THE POINT OF AN XRAY FILTER?

A

-placed over window of xray tube, absorbing the low energy part in the spectrum
-this is called hardening the beam, as it shifts the center of the spectrum towards the higher energy xrays
-low energy beams are not wanted as they are fully absorbed by tissue

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20
Q

WHICH TISSUES HAVE THE HIGHEST ABSORPTION OF ULTRA SOUND?

A

-muscle, fibrous tissue, calcifications and bone have the highest

-fluid and fat have the lowest

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21
Q

COMPUTED TOMOGRAPHY (CT)

A

-utilizes computer processed xrays to produce tomographic images or slices of specific areas of the body
-cross sectional images
-xray with detector and rotator
-mathematical modeling produces 3D image

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22
Q

SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT)

A

-tomographic imaging technique using a source of gamma rays which are projected into and through the body
-2D but produces true 3D images due to mathematical process
-cross sectional slices through the patient
-produce gamma rays via radionuclide active material which is injected into the body
EG: Tc 99m or I 123
-scintillators are devices which are able to acquire xray or gamma photons for next processing
-consist of a scintillation crystal and photomultiplier tube PMT which detect the photons
-functional cardiac or brain investigations

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23
Q

POSITRON EMISSION TOMOGRAPHY PET

A

-nuclear medicine imaging that produces 3D images of functional processes in the body
-positron emitting radionuclide is introduced into the body and used to detect pairs of gamma rays
-used heavily in oncology
-shortly lived and radioactive isotope tracers are usually incorpated in bodily compounds such as glucose water or ammonia
-as radioisotope undergoes positron emission decay it emits a positron and this can be traced to pinpoint location

24
Q

MAGNETIC RESONANCE IMAGING MRI

A

-used to visualize internal organs
-uses a large magnetic field and electromagnetic waves with high frequency
-no radiation load in comparison to CT so no risk
-body has a large amount of water, hence protons which get aligned in a large magnetic field (SIGNAL PRODUCED BY HYDROGEN NUCLEI IN WATER)
-electric magnetic field has a resonance frequency (perfect frequency) used to flip the spin of the protons in the magnetic field so that they are all aligned
-when electromagnetic field turned off, spins of protons return to equilibrium

25
Q

HOW DOES RADIATION THERAPY KILL CANCER CELLS?

A

-ionizing radiation damages the DNA of exposed tissue leading to cell death either by formation of free radicals (photon therapy) or direct ionization (charged particles)
-double stranded breaks is the most efficient strategy as cells have mechanisms to repair single stranded damage
-can also drain lymph nodes involved in the cancer
-to spare healthy tissues the beams are aimed from several angles to intersect the tumor only, providing a much larger absorbed dose than the healthy tissue itself

26
Q

WHAT IS TOTAL BODY IRRADIATION?

A

-therapy technique used to prepare the body for receiving a bone marrow transplant

27
Q

WHAT IS BRACHYTHERAPY?

A
  • a radiation source is placed inside or adjacent to the area requiring treatment in order to minimize exposure of healthy tissue during procedures to treat cancers of breast, prostate and other organs
28
Q

WHAT IS THE MAIN PHYSICAL FACTOR INFLUENCING THE EXTENT OF BIOLOGICAL EFFECTS OF RADIATION?

A

the absorbed dose (Gy)

29
Q

ULTRASOUND

A

-use non-audible mechanical waves
-1 to 20 MHz
-waves higher than 20,000Hz
-reflected waves processed to produce an image
-used for baby

30
Q

GALVANIC CURRENT

A

-electrotherapy
-current on constant intensity
-DC
-used for iontophoresis or trophic stimulation
-big risk is chemical damage under electrodes, HCL under anode, SODA LYE under cathode
-cant be used on patients with metallic implants
-substituted by galvanic intermittent current

31
Q

PULSE DIRECT CURRENT

A

-variable intensity, one polarity
-basic pulse shape may vary
-diadynamics, rectangular, triangular and exponential pulses of one polarity
-it can have stimulatory, trophic and analgesic effects

32
Q

ALTERNATING CURRENT

A

-safer and better tolerated by patients
-basic pulse shape may vary
-rectangular, triangular, harmonic sinusoidal, exponential or combined
-DC is zero which prevents damage
-patients with metal implants can undergo this
-much lower stress on tissue under cathode
-TENS, 4-pole interference, 2-pole interference, Isoplanar interference, Dipole vector field

33
Q

ANALGESIC EFFECTS

A

-pain is is based on the existence of a specific sensory system in which pain (nociceptors) respond to a signal and transmit it to the CNS

-gate system theory in which the posterior medullary horns lets through it only a limited amount of nerve impulses from the PNS, it can modulate its opening and closing based on different stimulations and can therefore decrease or increase the transfer of nociceptive information

-neuromodulation theory in which analgesic effect of some substances belong to a group of neuromodulators such as endorphins and encephalins produced in the CNS

34
Q

ANALGESIC

A
  • a drug which reacts to relieve pain
35
Q

WHICH ANALGESIC METHOD IS EFFECTIVE FOR ACUTE AND SEGMENTALLY LOCALIZED PAIN?

A

-low frequency currents of 50-150Hz
-intensity at or above threshold sensitivity
-stimulation of thick myelinated type A beta and delta nerve fibers

36
Q

WHICH ANALGESIC METHOD IS EFFECTIVE FOR CHRONIC PAINFUL SYNDROMES?

A

-low frequencies of 2-8Hz
-intensity at the highest tolerable level
-stimulation of thin C type nerve fibers
-leads to synthesis of endorphins

37
Q

WHAT IS A COMBINATION OF THICK AND THIN FIBERS?

A

-burst modulation
-carrier frequency of 100Hz
-burst frequency of 10Hz
-frequencies lower than 1Hz can be used

38
Q

WHICH PROCEDURES CAUSE A MYORELAXANT EFFECT?

A

therapeutic ultrasound, 2-pole interference with contour frequency 100-200Hz, 4-pole interference with high voltage therapy within the same frequency band

-> increased blood circulation improves washing away of acidic metabolites, increased LDH activity and efflux of Ca ions from muscles, in areas exposed to magnetic field

39
Q

WHAT CAN BE USED TO RELAX SMALL SUPERFICIAL MUSCLES?

A

paraffin

40
Q

DOES THE HYPERTROPHIC EFFECT OCCUR IN ALL THERAPY?

A

all but cyrotherapy

41
Q

WHAT CAUSES THE TROPHIC EFFECT?

A

hyperemia
-magnetic field accelerates healing of skeleton and soft tissues
-caused by better blood circulation in the exposed area and by irritation of the cytoplasmic membrane
-metabolism changes cAMP/cGMP ratio

42
Q

WHAT IS THE SOLUTION TO THE TROPHIC EFFECT?

A

galvanization can be recommended. Especially longitudinal (capillary hyperemia, vessel eutonization), low-frequency currents of the frequency 30 - 60 Hz and the intensity at or above the threshold motor activity level (muscle micro-pump) or ultrasound, laser, polarized specified achromatic light, vacuum-overpressure therapy
-also anti-edematous = antiphlogisitc effect of magnet and acceleration of healing and improved blood circulation

43
Q

CHRONAXIE

A

the minimum time an electric current that is twice the strength of the absolute minimum is able to depolarize a cell

NORMAL VALUE = LESS THAN 1MS, USUALLY 0.1MS OR LESS

FULLY DENERVATED MUSCLE = 30-50MS

44
Q

MOTORIC POINT

A

small area overlying a muscle where a slight visible contraction is most easily elicited with a minimal amplitude electrical stimulus
-> usually located near the proximal portion of the belly muscle

45
Q

AT WHAT FREQUENCIES DO MUSCLES GET CONSTANT CONTRACTIONS?

A

frequencies above 20Hz

46
Q

WHAT DOES THE STRENGTH-DURATION CURVE SHOW?

A

the interdependence between stimulus strength and the time required in activating muscles

47
Q

WHAT DOES NORMAL INNERVATED MUSCLE RESPOND TO?

A

-brisk twitch to a short duration pulse 1ms and to longer durations will respond with sustained or tetanic contraction

48
Q

HOW DOES A MUSCLE WHICH HAS LOST ITS PERIPHERAL INNERVATION RESPOND TO A STIMULUS?

A

-will not respond to a stimulus duration of 1ms or shorter but will respond to a longer stimulus duration in a sluggish manner

49
Q

RHEOBASE

A

-the minimal strength of an electrical stimulus of indefinite duration that is able to cause excitation of a tissue

50
Q

ACCOMODATION QUOTIENT

A

ratio of intensity of triangular and rectangular pulse which produce twitching with the same pulse length

NORMAL VALUE = 3
LIGHT LESIONS = 2.5 - 2.7

51
Q

VASODILATION EFFECT

A

caused by efflux of calcium ions which causes relaxation of muscles

52
Q

ANALGESIC

A
  • a drug which reacts to relieve pain
    -increased secretion of endogenous opioids caused my myorelaxation, antiphlogistic effects, antiedematous effects and presynaptic inhibition of nociceptive signals at the level of the medullary horns
53
Q

WHAT HAPPENS AT INCREASING FREQUENCY LEVELS OF ULTRASOUND?

A

-increase in tissue absorption
-decreasing discernment

54
Q

WHAT DETERMINES THE SPEED OF ULTRASOUND SPREAD IN THE TISSUE?

A

-elasticity and density of the tissue

55
Q

WHAT DOES 1 SMALL SQUARE OF ECG GRAPH MEAN?

A

0.1mV
0.04 sec

56
Q

WHAT ARE UNIPOLAR LIMB LEADS ALSO CALLED?

A

goldberger

57
Q

WHAT ARE UNIPOLAR PRECORDIAL LEADS ALSO CALLED?

A

wilsons

MEDICAL BIOPHYSICS (9 decks)

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