Imaging diagnostics physics Flashcards
Radiation classification (8)
Name types of radiation.
Waves (electromagnetic)
Radio waves
Microwaves
Infrared radiation
Visible light
Ultraviolet
X-rays
Gamma-rays
Corpuscular radiation types (3)
α-particles
β-particles
neutrons
The higher the radiation frequency, the smaller the
wavelength and vice versa.
X-rays originate from
the electron shells of atoms.
Gamma rays are emitted by
radioactive decay of atomic nuclei.
The atom consists of:
a positively charged nucleus that contains protons and neutrons.
A cloud of negatively charged electrons surrounds the nucleus.
The number of electrons in the
outer electron shell determines
the chemical properties of the
element.
Electron orbitals in the Bohr`s atomic model: the electrons move around the
atomic nucleus- electron shells.
The electron shells are labeled by
the closest to the nucleus K, L, M,
..
Each orbital electron has its specific energy level (binding energy), which is expressed as
a negative value.
The orbits closer to the nucleus have lower energy levels because
they interact more with the nucleus, and vice versa.
Ionizing radiation must be able to transfer enough energy to
an electron to liberate it from the atom.
(exam question!)
Ionization is…?
the emission of electrons from neutral atoms or molecules, which results in the formation of positive ions and free electrons.
“the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons”
Photon energy is usually expressed in
electron volts (eV).
Is MRI ionizing radiation?
Is ultrasound ionizing radiation?
(exam questions!)
MRI does not use ionizing radiation.
Ultrasound is based on non-ionizing radiation.
Ionizing radiation (X-rays, gamma radiation), is radiation that
carries enough energy to liberate electrons from atoms.
Ions are formed. The ion affects chemical bonds in molecules. The ion directly or indirectly affects biomolecule.
The radiation’s ability to ionize a substance makes radiation protection necessary.
Non-ionizing radiation is lower energy radiation such as
visible light, radio waves etc.
When the ionizing radiation (x-ray) absorbs, the substance does not become..
radioactive!
(e.g. neutron radiation does this)
The basic components of X-ray machine (4)
X-ray tube (vacuum) - containing an electron source (cathode) and target (anode).
Protective case and cooling oil between tube and casing.
Collimator- collimating beam shape.
High-tension generator - energy for accelerating electrons, possibility to adjust tube voltage, current and exposure time.
Describe X-ray tube construction/parts (min. 4)
The x-ray tube consists of a glass tube in which two electrodes are located:
Negative electrode- cathode
Positive electrode- anode (modern devices use rotating anode)
There is vacuum in the X-ray tube, so that electrons would not loose their energy.
Describe Production of X-rays
The heating filaments are heated and
thermionic emission leads to the release
of electrons from the cathode.
In the vacuum tube, the high voltage
power (20-150 kV) accelerates electrons
from the cathode to the anode (the
target).
The electrons move towards the anode
with positive potential, hit the anode disk
and lose their kinetic energy.
- 1 to 5% of this energy goes to X-rays, 95 to 99% of heat.
X-rays consist mostly of what type of radiation?
braking (Bremsstrahlung) radiation. (75%)
About 1/4 is characteristic radiation.
X-ray radiation energies vary.
Describe Braking (Bremsstrahlung) radiation
A small amount of the electrons reach the area near the anode atomic nucleus.
When an electron passes near the nucleus it is slowed (braking) and its path is deflected. Energy lost is emitted as a (bremsstrahlung)
X-ray photon (radiation).
Low energy braking energy is undesirable and gives poor quality radiographs.
Describe characteristic radiation.
Characteristic radiation is the electromagnetic radiation emitted when an electron from an outer shell of an atom transitions to fill an inner-shell vacancy.
When a high energy electron (1)
collides with an inner shell electron (2)
both are ejected from the anode atom
leaving a “hole“ in the inner layer.
This is filled by an outer shell electron (3)
with a loss of energy emitted as an X-ray photon (4).
Characteristic radiation is the most desirable type as it yields good images.
The collimator adjusts
the size and shape of the radiation field.
The field of light matches the radiation field.
The size of the radiation field is changed by removable tin plates.
To reduce patient exposure and scatter radiation, as well as to improve contrast, patient exposure area is collimated how?
as small as possible.
In addition, there is a filter/filters between the collimator and the X-ray tube that remove low-energy radiation components, thereby improving the quality of X-rays.
kV =
X-ray tube voltage or kilovolt (kV) =
the X-ray’s (photon) energy in other words penetration ability =
contrast of the radiograph
contrast of the radiograph can be adjusted using what parameter?
kV aka kilovolt aka tube voltage/penetration ability
mA =
milliamperage
X-ray tube current (mA) =
intensity of X-rays (photons) or in other words =
amount of X-rays (photons) =
image brightness aka exposure.
“the higher the mA, the more xrays you are sending to the anode plate”
image brightness of the radiograph can be adjusted using what parameter?
mA
milliamperage aka image brightness aka amount of individual xrays
“the higher the mA, the more xrays you are sending to the anode plate”
ms =
Exposure time (ms, millisecond) =
the time it takes to make an X-ray
the time it takes to make an X-ray is denoted..?
ms/milliseconds aka exposure time
The choice of exposure parameters
depends on (3)
the size of the patient, on study
region and (breed).
describe the image and what parameter you might adjust for a better quality image
underexposed image
If the radiograph is too light/bright (the X-ray density is too small), you must increase the amount of radiation (mAs).
describe the image and what parameter you might adjust for a better quality image
overexposed image
Decrease the mAs to reduce the number of X-rays emitted, thus reducing exposure.
describe the image and what parameter you might adjust for a better quality image
increased contrast so kV is low
Increase the kV to reduce the contrast and make the image appear less black-and-white, adding more shades of gray to reveal finer details.
describe the image and what parameter you might adjust for a better quality image
decreased contrast so kV is high
Lowering the kV increases image contrast by reducing the penetration of the X-rays.
This enhances the differences between tissues, creating a more distinct black-and-white image making the image less gray and improving the differentiation between different tissue densities.
Describe the Exposure parameters of this image.
overexposed so mAs is high
Describe the Exposure parameters of this image.
underexposed so mAs is too low
Describe the Exposure parameters of this image.
exposure, mAs, is normal/good
Radiation emerged from the anode passes
collimator and
spreads through the air to the patient.
X-rays path in the patient’s body: (3)
transmission (passing),
absorption,
scattering
describe xray
transmission (passing),
absorption,
scattering
Transmission: Part of the radiation passes
unchanged through the patient and moves forward to the detector (phosphor plate).
Absorption: Part of the radiation is absorbed in the patient. Radiation absorption is different in tissues of different sizes and densities. This part of the radiation is harmful to the
patient.
Scattering: Part of the radiation scatters in the patient, changes direction. In addition, the scatter radiation also radiates the surrounding staff.
Transmission and absorption are required for diagnostic information and making of the image.
Describe compton scattering.
involving the scattering of a photon by a loosely bound or free electron. This process results in the photon losing energy and changing direction, while the electron gains some of the photon’s energy and is ejected from the atom.
Compton scattering contributes to image degradation in X-ray imaging, creating a “fog” by introducing scatter radiation, which reduces image contrast.
Describe scatter radiation.
rays that have been deflected from their original path after interacting with matter, such as tissues in the body, air, or other materials.
Unlike the primary radiation beam, scatter radiation spreads out in various directions, contributing to unwanted radiation exposure and reducing image quality.
anti scatter grid in finnish
hila
the anti scatter grid is used when you have..?
and is unnecessary in..?
When you have bigger patients or bigger target areas.
Unnecessary in patients, which
weigh less than ~2 kg.
Why do you not use the anti scatter grid with small targets/patients?
Since the area is already so small, we don’t get much scatter radiation so using the anti scatter grid is useless.
An antiscatter grid absorbs a portion of both scatter radiation and primary radiation before it reaches the image receptor, reducing the overall exposure.
This results in a clearer, higher-contrast image (kV) by minimizing the “fog” created by scatter, but it also reduces the intensity of the X-ray beam that forms the image.
You would need to consider raising your xray power to compensate (mAs, milliampere-seconds).
This ensures that enough X-ray photons reach the image receptor to produce an adequately exposed image, maintaining the proper brightness (mAs) and detail.
kVp can also be slightly increased in some cases, but mAs is the primary adjustment.
Both mostly you can’t see any difference in smaller targets - only in larger targets.
Describe Shape distortion in xray images.
The greater the distance between the object being imaged and the image receptor, the more magnification occurs. This happens because the diverging X-ray beams spread out as they travel, enlarging the projection of the object onto the receptor.
An X-ray is a shadow image so angle and distance affect their size.
Keep the object as close to the image receptor as possible to reduce magnification. This helps minimize size distortion and ensures that the image reflects the true size of the object.
Black image depicts same target xrayed from different distances resulting in different size recorded.
Describe X-ray tissue densities
Different density and composition tissues have different radiation absorption.
The denser the tissue, the more radiation it absorbs. Bones absorb a large amount of
radiation.
Soft tissues - like muscles, fat and
internal organs allow more X-rays to pass
through them.
X-ray densities:
▪ Metal (and contrast media) – bright white
▪ Bone/calcification - white
▪ Soft tissue/liquid - light gray
▪ Fat - dark gray
▪ Gas - black
The CR (computed radiography) system captures radiographs on a
phosphor plate.
CR serves as an intermediate step between conventional film-based X-ray systems and fully digital radiography (DR).
CR systems utilize photostimulable phosphor (PSP) plates to capture and store X-ray images, which are later processed into digital form.
The MRI scanner uses what to capture images?
magnetic field, radio waves, field gradients and a computer to obtain images from the patient’s internal organs on different planes.
The measured MRI signal (electromagnetic) comes from target object.
MRI works in radio frequency spectrum.
In MRI, hydrogen nuclei are displayed.
Computed tomography uses what to capture images?
X rays, so ionizing radiation.
A 360 ° full rotation around the area of
interest is required to obtain the
image.
On imaging, the patient is in a donut-like gantry.
The device operator controls the
operation of the device using gantry
control panels and a separate operator
console computer, which is in an other
room.
Describe How ultrasonography works.
A transducer creates sound waves.
The transmitted sound waves pass
through the layer of skin, reflects off
of fluids, tissues and internal organs.
A reflection occurs at the boundary
between two materials if a certain
property of the materials is different.
The transducer receives reflected waves,
converts them into electric signals
and sends them into the computer.
The computer performs calculations
using the speed of sound and the
time taken by the echo to reach the
probe to create a real-time image of
the patient.
SPECT stands for
Single-photon emission computed tomography (SPECT).
Uses gamma camera
Possible to get 3D images
Is a type of nuclear medicine/ nuclear imaging modality.
PET stands for
Positron emission tomography (PET)
- Uses gamma camera
- Possible to get 3D images
Is a type of nuclear medicine/ nuclear imaging modality.
Radiation therapy uses ionizing radiation in order to..?
damage the DNA of cancer cells and
destroys their ability to reproduce.
When the damaged cancer cells are
destroyed by radiation, the body naturally
eliminates them.
Normal cells are affected by radiation, but they are able to repair themselves.
Radiation therapy can be a monotreatment or combined with chemotherapy and surgery.
Veterinary patient is placed into a specially made mold. This mold allows his body (and the cancer, marked with a blue cross) to be in the same position every day of treatment.
kV affects what
mAs affacts what
kV vs mAs
Memorize:
kV = contrast
increased kV = reduced contrast
decreased kV = increased contrast
mAs = exposure
increased mAs = overexposed
decreased mAs = underexposed
Memorize:
kV = contrast
increased kV = reduced contrast
decreased kV = increased contrast
mAs = exposure
increased mAs = overexposed
decreased mAs = underexposed
