RADIOLOGY EXAM 2

vacuum insert, electron source (cathode),  target material (anode), potential difference (kVp)

components of X-ray production

electrons accelerated towards target

How are X rays produced?

Cathode

source of electrons

Anode

target material

Electrons

What is emitted from cathode of an x-ray tube?

Tungsten

What is a typical anode target material?

Excitation, bremsstrahlung radiation (braking), and characteristic radiation (ionization)

What INTERACTIONS occur in X ray production?

Excitation (heat)

incident e- interacts with TARGET VALENCE shell e-

Excitation (heating)

MOST COMMON and LEAST USEFUL interaction in X ray PRODUCTION

Bremsstrahlung radiation

incedent e- has COULOMBIC interaction with target NUCLEUS 

Bremsstrahlung radiation

PRIMARY source of X-rays, SPECTRUM of x-ray photon produce

Characteristic radiation

incident e- EJECTS target INNER shell e-, OUTER shell e- fills space creating x-ray, HAPPENS IN XRAY TUBE

Characteristic radiation

generates DISCRETE energies of x-ray photon 

Focal spot

area of the ANODE where electrons from cathode strike

Smaller

What size focal spot creates SHARPER image?

More heat buildup/overheating

What is the downside of a SMALLER FOCAL SPOT?

more penetration/higher energy (less absorbed dose) and decrease contrast

Effect of HIGHER potential difference/kVp

kVP

Changes in the VOLTAGE between anode and cathode

increased dose (more x-rays), decreased noise, low-contrast detectability, better image statistics

Effect of INCREASED mA

mA

changes in CURRENT applied to filament, related to number of photons

increased dose

Effect of INCREASED exposure time

Exposure time

DURATION of current applied to filament 

increased quality and decreased dose

Effect of INCREASED filtration

Filtration

material absorbs low-energy x-rays REDUCING patient dose

Photoelectric effect

x-ray PHOTON is completely ABSORBED by an INNER-SHELL electron in TISSUE and causes it to be EJECTED

increased contrast and increased dose

What is the effect of PHOTOELECTRIC effect?

low energy photons, dense tissues/substances (bone/metal), high atomic number of tissue (Z)

What contributes to PHOTOELECTRIC effect?

Compton scatter

An x-ray photon hits an outer-shell electron, ejects it, and scatters with reduced energy

High-energy photons and soft tissue 

What contributes to COMPTON SCATTER?

Foggy and reduced contrast (image degradation)

What is the effect of COMPTON SCATTER?

Pt dose and occupational exposure

What is the main concerns with COMPTON SCATTER?

Classical scattering (rayleigh/coherent)

Low-energy PHOTON is deflected without energy loss

Image degradation

What is the effect of CLASSICAL/RAYLEIGH SCATTERING?

Transmission/no interaction

X-ray photon passes straight through the tissue

Dark areas (radiolucent)

What is the effect of NO INTERACTION?

Deterministic

Effects where SEVERITY increases with dose, SAFE THRESHOLD below which the effect does not occur

Stochastic

Effects where PROBABILITY increases with dose, but severity does not change. There is NO SAFE THRESHOLD

cancer and hereditary effects

Examples of stochastic radiation effects

Absorbed dose

The amount of energy radiation deposits in a material (like human tissue)

Equivalent dose

Adjusts the absorbed dose based on the TYPE of RADIATION

Effective dose

Adjusts the equivalent dose based on TYPE of TISSUE where exposed and how sensitive they are

small dynamic range, one location at a time, wait time

Cons of Film-screen system

wide dynamic range, portable, no wait time,  increased dose efficiency 

Pros of Digital systems

high cost, bulky sensor, decrease quality

Cons of Digital systems

charge-coupled devices (CCD), metal oxide semiconductors (CMOS), flat panel display (FPD)

Types of digital receptors that are Solid state detectors

charge-coupled device (CCD)

Charges are shifted pixel by pixel across the chip to a corner, SLOW READ OUT

Complementary metal oxide semiconductors (CMOS)

Each pixel is isolated from its neighboring pixels and directly connected to a transistor, FASTER READ OUT than CCD

Flat panel detector (FPD)

Uses a large area panel with amorphous silicon, used in CBCT and PANO

Photostimulable phosphor

imaging plates that store x-ray energy to form LATENT IMAGE in semiconductor lattice and later release it as light when scanned by a laser

Relationship between input/output of imaging system

What does a Hurter and Driffield curve show?

More contrast

What does a STEEPER Hurter and driffield curve indicate?

film

Which type of receptor has a STEEPER Hurter and driffield curve and thus INCREASED CONTRAST?

digital

Which type of receptor has a WIDER dynamic range on Hurter and driffield curve and thus is EASIER to get USABLE IMAGE?

Spatial resolution

capacity to distinguish fine detail/ see tiny objects

detector pixel size, voxel size, focal spot size, motion, recon kernel (filter)

What affects spatial resolution?

low-Contrast resolution

ability to distinguish between tissues with SLIGHT DIFFERENCES in DENSITY or signal intensity (i.e., “low contrast” between them)

kV, noise, recon kernel (filters)

What affects low-contrast resolution?

detection of similar-looking objects (ex: white and gray matter)

what does a HIGH LOW-CONTRAST resolution indicate?

MRI

what type of imaging has the best (highest) LOW-CONTRAST resolution

detection of small objects

what does HIGH SPATIAL resolution indicate?

Higher bit depth

What creates better contrast resolution?

Bit depth

number of gray levels a pixel can show

Sharpening

removing LOW frequency noise

Smoothing

removing HIGH frequency noise

CT dose index (CTDI)

estimates the dose delivered per slice during a CT scan

Dose length product (DLP)

total radiation dose across the length of the scan

Against phantom (not patient)

How are effective doses estimated?

CT number/ hounsfield units

numerical value assigned to each voxel (3D pixel) in a CT image that reflects the DENSITY of the tissue

More dense material (bone, metal ect)

What does a LARGER CT number/ hounsfield unit indicate?

Less dense material (air, tissue ect)

What does a SMALLER/NEGATIVE CT number/ hounsfield unit indicate?

Interaction of magnetic field, hydrogen ions, and radiofrequency (RF) pulse

How do MRI machines work?

Gradients

magnetic fields that vary in strength and direction across different parts of the body, used to localize the MRI signal

T1

time it takes protons to REALIGN with B0

Tissues with short T1 (ex:fat)

On a T1 weighted image what type of tissue would appear bright?

Efficient energy transfer, less water/high fat

What causes tissue to have a SHORT T1?

T2

time it takes for protons to DEPHASE

Inefficient energy transfer, High water, low density (ex: CSF and inflammation)

What causes tissues to have a LONG T2?

Tissue with long T2 (ex: water/CSF)

On a T2 weighted image what type of tissue would appear bright?

B0 field

static magnetic field that causes protons to spin

Signal excitation

radiofrequency (RF) pulse applied at the Larmor frequency, that temporarily knocks the aligned protons out of alignment

larmor frequency

The frequency at which protons precess (spin) in a magnetic field, determined by the strength of the magnetic field and the type of nucleus being observed

Spatial localization

utilization of GRADIENT coils to understand where signal is coming from

MRI

What is the superior imaging for soft tissue?

Absorption of RF energy in protons causing their relaxation

How are MRIs created?

Protons emit RF signals that induce currents in nearby scanner

How is signal detected in MRI?

Contrast agents

gadolinium-based agents that SHORTEN T1 relaxation time, making areas (like tumors or inflamed tissues) appear brighter

Few protons and short T2 relaxation

Why is it challenging to MRI teeth?

effective dose

which radiation dose quantity is most used in expressing radiation risk?

exposure

measure of radiation field intensity in air

Kerma

describing the energy transferred from RADIATION to MATTER.

higher

what RADIATION weighting factor is MORE biologically DAMAGING when comparing different types of radiation?

more sensitive tissues (to radiation)

what does HIGHER weighting factor of TISSUES indicate

radon

what contributes the most to BACKGROUND radiation

radon

second most frequent cause of lung cancer

photoelectric and Compton scattering

ionizing interactions that x-rays have with matter

indirect actions (radiolysis of water and free radicals)

what causes most of DNA damage from ionizing radiation.

mitotic rate and degree of differentiation

what influences cell sensitivity to death by radiation

rapidly dividing cells

what kind of cells are more RADIOSENSITIVE to ionizing radiation.

postmitotic specialized cells

what kind of cells are more RADIORESISTANT to ionizing radiation

thyroid gland (followed by salivary gland)

most sensitive tissue/organ exposed during head/neck imagining