simulation review handout

the filtered back projection is a reconstruction process in

CT

what receives attenuated radiation when using CT

diodes

Magnetic and radiofrequency waves to generate images.

MRI

Body consists of 67% of ______

hydrogen

the odd number of protons and neutrons in the nucleus causes these atoms to act like little

magnets

The _______ contains piezoelectric material produce sound waves that move through the body and during their travel they are reflected or refracted back as echoes.

transducer

Takes advantage of the body’s metabolism like amount or rate of amino acids, molecular O2 and glucose.

PET

most commonly used PET radiopharmaceutical

FDG

FDG is a _______ emitter and when emitted it pairs up with an electron causing an annihilation reaction with release of 2 protons

positron

The process of designing a precise mock-up of the patient’s treatment

treatment planning simulation

A double check prior to treatment delivery

verification simulation

A CT image-based process that uses 2D and 3D reconstructions of the patient

virtual simulation

The process of defining the geometrical position and extent of the tumor or anatomic structures in reference of surface marks that can be used for treatment setup purposes

localization

A line perpendicular to the cross section of the simulation or treatment field

central axis

The only imaginary line emanating from the source (focal spot) of radiation that is NOT divergent

central axis

Transverse axis that extends right to left in the patient

x

Longitudinal axis extending head to foot

y

Axis extending upward from the tabletop

z

Treatment fields determined 1st , target volume 2nd, & field shaping 3 rd

conventional sim

Target volume defined 1st, then fields are shaped to conform to defined volume.

CT sim

Defined as combining 2 or more sets of image data

image fusion

the process of estimating an optimal transformation between two images

image registration

image registration based on bony anatomy

rigid body

image registration that is much more complex but effective process

deformable

Process of obtaining image data regarding tumor and organ motion

4D

Provides a model of breathing motion to be used in planning and treatment delivery

4D

_______ is one of the weakest link in treatment planning and delivery

immobilization

Treatment target must be irradiated uniformly to + or – ___% for adequate tumor contro

5

Also known as high contrast resolution

spatial resolution

Describes the degree of blurring in an image. Ability to distinguish between two adjacent high contrast structures

spatial resolution

_______ slice thickness, pixel size, detector size, field of view will help improve spatial resolution

Decrease

Also known as low contrast resolution

contrast resolution

Ability to distinguish between similar tissues

contrast resolution

_______ matrix size will improve contrast resolution

decrease

_________ field of view, slice thickness, pixel size, mAs will improve contrast resolution

increase

Occurs due to an insufficient number of photons reaching the detectors, equipment limitations, or due to reconstruction filters (CT image grainy or speckled)

noise

_______ display FOV, slice thickness, pixel size, kVp & mAs will help improve noise

increase

______ of matrix size will improve noise

decrease

Common slice thickness of non-IMRT planning is

5mm

Common slice thickness for IMRT planning is

2-3mm

Common slice thickness of SBRT or SRS may require _____ or less

2mm

Determines the area, within the gantry, from which raw data is acquired

scan field of view

Also called the reconstructed field of view or RFOV

display field of view

Determines how much of the collected data is used to create the CT image

display field of view

Window _____ determines the QUANTITY of HU represented by shades of gray

width

________ width (50-500HU) improves image contrast and is better for similar tissues

Narrower

Determines image contrast

window width

Window ____ determines the RANGE of HU units that are displayed

level

Determines image brightness

window level

_____ window level = Bright Image

low

An increase in kVp results in an increase in the energy of the x-ray beam and a harder beam. Attenuation is determined by both the amount and density of tissue the beam penetrates, and various areas of the body attenuate the beam differently because the human body is not uniform

beam hardening artifacts

These occurs when similar tissue types share the same voxel, and therefore, the tissues are averaged as one Hounsfield unit

partial volume averaging artifacts

These often appear as ghosting on the image. The image has fuzzy edges that do not define the anatomical borders correctly. This artifact diminishes the ability of the radiologist to accurately interpret the CT exam. Patient motion artifacts are caused by both voluntary and involuntary movement

motion artifacts

When impurities are present in the CT x-ray tube, a short circuit can occur causing tube arcing

equipment artifacts

Ring artifacts

faulty detector

Artifacts, which can be high or low frequency, arise from insufficient projection samples. Low-frequency artifacts appear as shadowing on the image and usually are corrected by using interpolation

cone beam artifacts

Caused by the abrupt longitudinal changes of the body. These types of artifacts are more difficult to address and are usually corrected by using specific algorithms. Characterized by streaks

high-frequency artifacts

Appear as streaks that originate from body structures that vary in tissue density

edge gradient artifacts

Ghosting, shading or blurring

motion artifact

Star or streak

metal artifact

Tube arcing

equipment artifact

Streaks

edge gradient

Ring

faulty detector

Broad Streaks

beam hardening