rads 301 mt 1 content

which imaging techniques do not use ionizing radiation?

MRI and ultrasound

what imaging techniques use ionizing radiation?

CT, X-Ray, PET

what two phenomena explain X-ray generation

Brehmsstrahl reaction and characteristic radiation

what two phenomena explain X-ray attenuation

compton scatter and the photoelectric effect

what is the Brehmsstrahl Reaction?

when the high speed electrons are shot at the anode, the electrons slow down as they approach the nuclei in the anode. the lost kinetic energy is converted into an X-ray photon.

what is characteristic radiation?

when the high speed electrons knock out an inner shell electron, an outer shell electron will fill the vacancy. the outer shell electron is moving into a lower energy state when becoming an inner shell electron, so the difference in energy is released as an x-ray photon.

what is the photoelectric effect

when photons hit an atom, a photoelectron is ejected. the leftover atom becomes an ion, and the photoelectron ionizes other atoms

what is compton scatter?

when the x-ray is not fully attenuated by the electron, the leftover photon energy is released at an angle and creates scatter → makes image less detailed

how does the atomic number and density of an atom affect imaging

atoms with high atomic numbers and high density will attenuate more X-rays, appearing white in the image

atoms with low density and low atomic numbers will not attenuate as many X-rays, appearing black in the image

who discovered the X-ray

Roentgen

what is the term for tissues with higher density that attenuate more x-rays

radiodense

what is the term for tissues with lower density that attenuate less x-rays

radiolucent

what makes a CT different from an X-ray scan

• takes longer

• has a rotating x-ray source

• has better detail

• higher radiation

what is the similarity between CT and X-ray scans

both create maps of tissue density using x-rays

what is the unit of a CT and how is it rated?

Hounsfield Units are based off the density of water (0). anything denser than water is >0. anything less dense than water is <0.

what is the difference between taking an anterior-posterior vs. posterior-anterior x-ray scan?

AP scan sends x-rays from front to back; creates magnification of mediastinal shadow by 20-25%

PA scan sends x-rays from back to front; creates a clearer image

how does the MRI work

a strong magnet sends different radiofrequency pulse sequences to excite protons. receiver coils read the energy released by the protons when the relax into their new energy level.

why does MRI have great soft tissue contrast compared to other imaging methods?

water and fat have lots of protons, so they react well to radiofrequency pulses compared to x-rays that are based off of density

types of MRI images

t1-weighted and t2-weighted

what happens in a t1-weighted image and what does it highlight

a short TR and TE highlights fat; good for structure detail and anatomy

what happens in a t2-weighted image and what does it highlight?

a longer TR and TE which highlights water and fluid containing spaces; good for pathology of tumors, edemas, etc.

strengths of MRI

no radiation (good for women and children), good soft tissue contrast

weaknesses of MRI

expensive, inaccessible, takes longer to generate images, strong magnet may have complication risks

what is the longitudinal axis of an MRI

the time it takes for a proton to realign with external magnetic field

what is the transverse axis of an MRI

time it takes for protons to relax to a new baseline frequency

how does an ultrasound work

high frequency sound waves travel through tissue and are reflected back to a probe to generate an image

what is a hypoechoic tissue

a tissue that reflects little/no ultrasound signals → appears black

what is a hyperechoic tissue

tissue that reflects lots of ultrasound signals → appears white

what kind of images will low frequency ultrasound create

low resolution but better depth

what kind of images will a high frequency ultrasound create

high resolution but poor depth

what is acoustic window and how does it work?

using fluid filled spaces to get a better view of deeper structures. this occurs because the sound waves travel well through the fluid, creating a better image,

applications of ultrasound

pregnancy, evaluating heart function, blood clots, muscles and tendons, and abdominal organs

what is an echocardiogram and what is it for

ultrasound of the heart that gives anatomical and functional information in real time → can show contractility, blood flow, and anatomy

what is hypertrophic cardiomyopathy and what is its etiology and prevalence?

thickening of the septum or left ventricle of the heart, causing blockage of the aorta, which can lead to sudden cardiac death.

occurs in 1/500 and is the leading cause of SCD in the young.

what is the leading cause of death in men and women

cardiovascular disease; 1/5 women

what is the most common genetic myopathy?

hypertrophic cardiomyopathy

best noninvasive test for coronary artery disease assessment

CT

acute chest pain, normal enzymes, normal/non-diagnostic ECG may indicate what?

coronary artery disease

first line of imaging for the chest

chest x-ray

uses for chest x-ray

• emergency line placement

• post surgical imaging

• pneumonia, pneumothorax

• shortness of breath

what does blunted costophrenic angles indicate

pleural effusion (fluid buildup) or thickening

pneumothorax cause

air enters the pleural cavity, disrupting surface tension and collapsing the lung

types of pneumothorax

open pneumothorax: pleural cavity pressure < atm pressure

closed pneumothorax: pleural cavity pressure = atm pressure

tension pneumothorax: pleural cavity pressure > atm pressure

strength of CT scan

• great bone and lunge anatomic detail

• good contrast and spatial resolution

• can do CT angiography, cinematic rendering

weakness of CT scan

• high radiation

• weight limit

• possible complications

ray tracing

simulation of how light rays bounce off objects when 3d rendering

global illumination

figuring out shadows, depth, and contrast in 3d rendering

what is cinematic rendering

3d rendering using cross sectional images to make them photorealistic

differences between cinematic rendering and volume rendering

lighting model

realism

detail

computation amount

advantages of cinematic rendering (CR)

• enhanced realism and clarity for visualization of anatomy

• effective communication

• chance for innovative research and accurate surgical planning

• improved diagnosis

cons of cinematic rendering

• high computational demands

• can’t be used as a standalone diagnostic tool

• potential for artifacts

what is the precentral gyrus made of

grey matter

what is the internal capsule made of

white matter

what is the function of the caudate and lentiform nuclei

tuned movements

types of ultrasound probes

linear, curvilinear, phased array

what is a linear probe for?

low imaging depth; arteries, veins, soft tissue, musculoskeletal system, breast, pleura, eyes, testes

what is a curvilinear probe for

medium imaging depth; abdominal organs, abdominal aorta, abdominal free fluid

what is a phased array probe for

deep imaging depth; heart, lungs, abdomen, pleura, inferior vena cava

ultrasound artifacts

acoustic shadowing, color doppler, comet tail, mirror image, reverberation

what is refraction and what does it cause?

when an ultrasound wave hits a surface and changes its angle of insonation; causes some edges to be brighter than others and can cause acoustic shadowing or mirror image

what is acoustic shadowing

when an ultrasound wave refracts or is completely absorbed by a high density structure, obstructing the view of structures below/behind it

what is mirror image

when an ultrasound wave bounces off a structure and strikes another mass, causing the wave to take longer to return to the probe. this creates a duplicate of the mass.

what is reverberation

when ultrasound waves bounce off the probe or off a returning surface and creates lines and reflections

what is comet tail

when an ultrasound wave bounces off a highly reflective object (ie. calcification), it may cause linear reverberation below the object

what is twinkling phenomenon

when intrinsic ultrasound waves bounce within the machine and cause alternating colors below a reflective object in color doppler mode

what is b-mode for

brightness mode is the a-mode but it scans th whole plane

what is m-mode for

motion mode is used to show movement over time (contractility over time)

what is color doppler for

shows direction and velocity of flow; blue=away from transducer, red=towards transducer

cinematic rendering process

1. collection of data

2. assigning opacity and colors to different voxels

3. path tracing (monte-carlo)

4. image generation

what is mote-carlo path tracing

a formula/equation used to calculate and integrate all the different light scattering from different directions to reduce compuation