Final Flashcards
Current Scanners
No longer single slice
Data collected as a continuous data stream
Single breath hold for the patient
Entire body can be done in less than a minute
1st generation took 5 minutes for a single slice
Spiral scanners are acquiring 900 slices in under a minute
Resolution
Is the ability to image two separate objects and visually distinguish one from the other.
Spatial resolution is the ability to image small objects that have high subject contrast. Ex: bone-soft tissue interface, breast calcifications, calcified lung nodule
Conventional radiography has excellent spatial resolution
How does a CT scanner work?
X-rays are generated in an x-ray tube in the same way x-rays are generated for a radiograph
High voltage(120-150kV for CT) is used to drive electrons across the tube striking the target
Higher voltage results in higher energy photons which mean fewer photons are absorbed in tissue
This is important because photons that are absorbed create deficits at the detectors which result in artifacts
Photons are detected by a detector(s) and quantified
The detectors are essentially DR plates
The data is then processed into an image
CT Imaging System
Operating console—two or more monitors Patient data annotation Management of imaging technique, gantry movement, contrast injection, image reconstruction Computer Microprocessor Primary memory Gantry X-ray tube Detector array HV generator Table
Pixel and Voxel
Field of view (FOV) = diameter of image reconstruction
Pixel size = FOV/matrix size
Voxel = pixel area × slice thickness
CT Image Quality:
Digital Image Quality
Spatial resolution
The ability of an imaging system to RESOLVE and render on the image a HIGH CONTRAST object (shades of gray differences in close objects to one another)
Contrast resolution
The ability of the imaging modality to distinguish between differences in image intensity. Remember, the more densities you can visualize the more anatomy you can see.
Advantages of spiral v. conventional CT
Faster image acquisition Contrast can be followed better Reduced patient dose at pitches > 1 Physiologic imaging Improved 3d and reconstructions Less partial volume Fewer motion artifacts No misregistration Increased throughput Real time biopsy
Hybrid PET/CT
CT/MRI provides anatomic detail
Diagnosing, staging and restaging cancer
Obvious structural disruptions, necrotic, scar tissue, inflammatory changes. Lymph nodes that are enlarged, malignant or benign?
Nuclear Medicine
Developed molecular imaging, physiology of cells
Positron Emission Tomography
PET provides functional information
CT provides structural information
Key factor: Radiotracer fluorine-18 fluorodeoxyglucose (FDG)
Hybrid PET/CT
PET and CT can be done separately, the most complete diagnosis comes with a combination of modalities
Aligning images acquired on two different scanners is a complex problem
PET
Essential tool in the management of cancer patients
Diagnosis and accurate staging
Staging determines the extent and distribution of disease influencing choice of treatments
How Does PET Work?
FDG-PET – radiation is given off when positrons (antimatter electrons) encounter electrons in the body
Radiopharmaceutical emits positrons that encounter electrons in the body
They annihilate each other, producing high-energy photons that can be detected by the imaging device
The pharmaceutical portion of FDG is glucose that allows localization that favor glycolysis
Increased glucose uptake is associated with malignancies, more glucose uptake more aggressive malignancy
PET can create images of blood flow and metabolism
PET can detect functional changes before structural changes (CT and MR)
Glucose metabolism is a normal physiologic function of brain, muscles, salivary glands, etc
Timing of the patient’s last meal, insulin injection, and level of hydration can affect PET results
Patients are NPO 4 to 6 hours before a PET exam.
Determining Protocol
PET Exam
CT Exam degree of quality
CT images for attenuation correction and localization only or more detailed anatomic images. IV and/or PO contrast, etc.
Using CT for Radiation Treatment Planning
Radiation treatment planning team, oncologists, radiation therapist, medical physicists and medical dosimetrists plan the appropriate external beam radiotherapy or internal brachytherapy treatment for cancer.
Imaging
Typically CT is the primary set of images
MRI can be used for soft tissue contouring
PET is less commonly used.
Radiobiology
The study of the effects of ionizing radiation on biologic tissue
Most radiobiology research is designed to develop dose-response relationships to determine the effect of planned doses or accidents
X-rays are harmful, low energy photons can cause skin burns, cancer, leukemia
Early measurement of Radiation
Skin dryness and erythemia Ulcers formed Late Effects: Cataracts Cancers
ALARA
As Low As Reasonably Achievable
Natural Radiation
Natural radiation accounts for approximately 3 mSv (300 millirem, mrem)
3 sources of environmental radiation: cosmic rays, terrestrial radiation and internally deposited radionuclides. The largest source of natural radiation is radon.
Deterministic (non stochastic) vs. Stochastic
Even though radiation can be of great benefit, too much exposure can be dangerous. There are two types of radiation effects:
- Effects that will occur given enough exposure (or threshold effects)
- Effects that have a higher chance of occurring as you receive higher amounts of exposure (or chance effects)
Acute Radiation Syndromes
Radiation Exposure Accidents Chernobyl (30 deaths due to ARS) Three Mile Island (0 deaths) Fukushima (0 deaths) 3 separate syndromes Hematologic death Gastrointestinal (GI) death Central nervous system (CNS) death
Response Stages Following
Lethal Level of Radiation Exposure
Prodromal Period
Begins minutes to hours after exposure
Lasts hours to days
Nausea, vomiting, diarrhea, leucopenia
Latent Period
Symptoms recede
Lasts hours to weeks
Manifest Illness
LD50/60 for Various Species
50% of the irradiated subjects to die w/in 60 days
Local Tissue Damage
deterministic radiation response
minimum necessary to cause a change
threshold-type dose-response
severity of the response increases with increasing dose in a nonlinear fashion
Skin erythema
5000 mGy
annual occupational dose limit 50 mGy
Hemopoietic System
Bone marrow, circulating blood, and lymphoid tissue
deterministic radiation response
minimum necessary to cause a change
threshold-type dose-response
severity of the response increases with increasing dose in a nonlinear fashion
Hemopoietic Depression
Cells renew over time
Effects on the Gonads
Doses as low as 100 mGy
Stochastic Effects
Chance effects
Results when low doses are delivered over a long period
More associated with the type of exposure associated with medical imaging .
Malignancy and genetic effects
Life span shortening and effects on local tissue
Risk Estimates
Relative risk Observed cases/Expected cases Excess risk Observed cases/Expected cases Absolute risk Number of cases/106 persons/rad/yr
Radiation-Induced Leukemia
Latent period = 4–7 years
At-risk period = 20 years
Radiation-Induced Cancers
Observed in Irradiated Populations
Thyroid cancer Thymus irradiation Rongelap Atoll nuclear test Bone cancer Radium watch dial painters Radium salt treatment Skin cancer Orthovoltage radiation therapy
Breast cancer Tb treatment A-bomb survivors Lung cancer Uranium miners Liver and spleen cancer Thorotrast
Fertility and Pregnancy Risks
Low doses of radiation have no effect on fertility. Effects in fertility is a deterministic effect.
Exposure during pregnancy can present some increased risk to the fetus.
Two at risk populations
Patients and Technologists
Pregnancy and Radiation
Since their cells are reproducing more often, developing embryos, fetuses, and children are typically more sensitive to radiation than adults.
When the abdomen of a pregnant woman is exposed to radiation, a fraction of that exposure is also received by the embryo or fetus.
Effects of radiation in utero are time and dose related
Effects include:
Prenatal death, neonatal death, congenital abnormalities, malignancy inductions, general impairments of growth, genetic effects, and mental retardation.
Pregnancy Risks
Within 2 weeks of fertilization with a very high dose the outcome is spontaneous abortion.
First 2 weeks all-or-nothing risk.
Estimates conclude that a high dose during the first 2 week of pregnancy will increase the rate of spontaneous abortion by 0.1%
Normal incidence of spontaneous abortions are 25 – 50%
Deterministic Effects (non stochastic) = threshold, nonlinear
Hematologic depression, erythema, epilation
Stochastic (chance) = nonthreshold, linear
Malignancy, genetic effects, life span shortening
Radiation Protection Features of a Radiographic Imaging System
Source-to-Image Receptor Distance Indicator Collimation Positive-Beam Limitation Beam Alignment Filtration Reproducibility Linearity Operator Shield
Fluoroscopic Protection Features
Source-to-Skin Distance Primary Protective Barrier Filtration Collimation Exposure Control Bucky Slot Cover Protective Curtain Cumulative Timer Dose Area Product
Occupational Monitoring
Required when someone may receive more than 10% of the recommended dose limit.
5 Rem/yr
Monitoring is not protection, it is awareness
Location of the Monitor
Ideally, at the collar outside on the lead apron.
Extremities
At the waist
Typically during pregnancy
Monitoring Report
Must include
Current exposure
Annual exposure
When leaving employment or school exposure should move with you
Protective Apparel
Aprons
Gloves
Thyroid shields
Glasses
All of these are required to have a minimum lead thickness of 0.25 mm
They are designed to stop scatter radiation NOT PRIMARY
Technologist Position
In the room you should always be as far as possible from the patient and beam You should never hold patients Image receptor May be controllable, most likely not Patient positioning Correct positioning minimizes repeats AP versus PA may reduce dose Shielding Blocks the beam Reduces dose
Reduction of Patient Dose
Unnecessary exams Typically, you cannot control this Repeat exams This you can control and are expected to control Radiographic technique Totally within your control Using proper SOD, source object distance
Atoms and molecules are the fundamental building blocks of
Matter
The formula e=mc2 represents
Nuclear power
Ionizing radiation is capable of removing
electrons
Biggest source of man made radiation
Diagnostic x-rays
Exposure is measured in
Grays
Today Radiology is considered
A very safe operation
ALARA means
As low as reasonably achievable
Filtration is used to absorb
low energy x-rays
Photons with the highest frequencies have the
Shortest wavelength
Which scientist discovered x-rays
William roentgen
Crookes
Smallest particle all the properties of an element
Atom
Positively charged nucleus surrounded by negatively charged electrons is
Bohr Model
Atom in normal state is..
Electrical charge is 0
Binding energies is represented by
Shells
Atom same number proton but different number neutrons is called
Isotope
Atoms combines form is called
Molecules
Atom looses or gains electrons
Ion
Innermost electron shell is
K
A chemical compound is any quantity of
one type of molecule
during beta atom releases
electrons
the only difference between gamma and x-ray is their
origin
smallest electromagnetic radiation
photon
rise and fall of sin wave is
frequency
wavelength beam of electromagnetic radiation is increases by factor of 2 then frequency is
decreased by half
the reduction of radiation intensity due to scattering and absorption is called
attenuation
the lowest energy range of electromagnetic spectrum is
radio waves
photons tend to interact with matter
equal in size with their wavelengths
smallest unit of charge is
the electron
like charges repel unlike charges
attract
on the surface of an electrified object the charges concentrate on
the sharpest curvature
a battery is a source of
direct current
Ohms law
I=V/R
Rubber and glass are
insulators
the magnetic intensity of an electromagnet is greatly increased by the addition of an
iron core
an alternating ac current is represented by
a sinusoidal line
us alternating current goes through a complete cycle every
1/60 seconds
is defined as the ability to image two separate objects and visually detect one from the other
resolution
Higher speed image receptors generally produce images with
increased noise
In general radiography, the useful optical densities lie between _____ and _____.
0.25, 2.5
The best way to minimize magnification is to use a
long SID, small OID
Distortion can be reduced by
placing the object plane perpendicular to the image plane
The bit represents
zero or one.
In computer language, 2 bytes is a
“word.”
Projectile electrons travel from
cathode to anode
During an exposure, most of the kinetic energy of the projectile electrons is
converted to ________.
heat
The efficiency of x-ray production is not affected by
the tube current.
Electron interactions at the inner-shell of the target atoms produce
characteristic radiation
Characteristic x-rays are produced by __________________.
released binding energy
The quantity of bremsstrahlung radiation increases proportionately with
increased _____.
mAs
The quality of an x-ray beam is higher when the peak of the emission
spectrum is further to the___________.
right
The number of x-rays in the useful beam defines x-ray ________.
quantity
X-ray quantity increases in direct proportion to increases in __________.
mAs
the distance from the source to the image (SID) is reduced by half, how is the
x-ray intensity at the image affected?
It is increased 4 times.
Beam quality is affected by ______________.
kVp and filtration
X-ray beam quality is improved by ____________.
increasing filtration
The two primary forms of x-ray interaction in the diagnostic range are
________________.
Compton scattering and photoelectric absorption
An incident x-ray interacts with an atom without ionization during
______________.
coherent scattering
Which x-ray interaction involves the ejection of the K-shell electron?
Photoelectric absorption
Compton scatter is directed at _____ angle from the incident beam.
any
In ________________, there is complete absorption of the incident x-ray photon.
photoelectric interaction
___________ occurs only at the very high energies used in radiation therapy and
in nuclear medicine P.E.T. imaging.
Pair production
K-shell binding energy increases with increasing ____________.
atomic number
Which has the greatest mass density?
Bone
Barium is a good contrast agent because of its __________________.
high atomic number
Computed radiography screens respond to radiation with
______________________.
photostimulable luminescence
The computed radiography cassette is called a(n) ______________ plate.
imaging
The principal source of noise in computed radiography is
____________________.
scatter radiation
The digital imaging plate can sit for some time after the erase cycle.
False
Digital imaging techniques are always applied to ___________________.
computed tomography, ultrasound, magnetic resonance imaging.
In digital radiography, the brightness of the image is determined by
_______________.
pixel values
In digital radiography, spatial resolution is improved with increased
_____________.
matrix size
The dynamic range determines the degree of __________________ in the
image.
contrast resolution
Spatial resolution is determined by the ratio of ________________ to
____________.
field of view, matrix size
Conventional x-ray tubes and cassettes are used with ________ radiography
systems.
computed
Radiographic image quality is improved when the __________ is increased.
source image distance
If 5% of an incident beam is transmitted through a body part, then 95% of that
beam was ______________.
attenuated
A charge-coupled device used in digital fluoroscopy provides high _________________.
spatial resolution signal-to-noise ratio detective quantum efficiency
Digital fluoroscopy with a charge-coupled device has lower patient dose and higher
light sensitivity than
conventional fluoroscopy.
A principal advantage of digital fluoroscopy is the ______________.
image subtraction
The combination of temporal and energy subtraction techniques is called _________.
hybrid subtraction
Hybrid imaging can produce the highest-quality digital fluoroscopy images only if
_________________.
patient motion is controlled
Digital fluoroscopic dose rate is lower than that for continuous analog fluoroscopy.
True
When doing soft tissue radiography, the differential absorption between ________ and ______ must
be enhanced.
muscle, fat
The breast tissue tends to be increasingly _________ in older women.
fatty
About 50% of breast cancer occurs in the __________ quadrant .
upper outer
It is recommended that women obtain their first baseline mammogram before the age of _____.
40
A dedicated mammography unit should have an automatic adjustable _____________
compression device.
A target of molybdenum or rhodium is preferable in mammography because it reduces the
_____________.
scatter
Breast compression has the advantage of lowering _________________.
patient dose motion blur superimpositions
Breast compression is used to lower patient dose and ________
reduce focal spot blur.
Distance and attenuation are
directly related
Higher frequencies have/has more attenuation while lower frequencies have____________
less attenuation
Of the following what contributes to attenuation.
reflection scattering absorption
As sound strikes the boundary layer between tissue interfaces, some of the sound is reflected back to
its source
true
Scattering results in____ of sound
random redirection
The half value layer thickness is the distance sound must travel in a medium that reduces the
intensity of sound to ½ its original value (intensity)!
true
during ultrasound imaging higher frequencies result in ________
higher quality images.
Most of the energy in ultrasonic imaging is converted to ______ during absorption
heat
Spatial frequency is used to describe the quality of spatial resolution in terms of _____________.
line pairs
In digital imaging, spatial resolution is ultimately limited by ___________________.
pixel size
The human visual system can distinguish ________ shades of gray.
30
The number of gray shades that an imaging system can reproduce is called its ________________.
dynamic range
The bit capacity of each pixel identifies the ___________ of a digital imaging system.
dynamic range
As mAs is increased the signal-to-noise ratio is ____________.
increased
Image detail is also called _______________________.
spatial resolution
With digital imaging, patient dose can be reduced by using higher ______ techniques.
kVp
In MRI imaging the typical matrix size is _____
256 x 192
of the following which has the lowest spatial resolution?
MRI
Most MRI images are acquired after two minutes with some sequences taking _______
more time.
MRI is a safe imaging procedure that can be utilized for any patient with limitations. These limitations
may include:
patients with a pacemaker
MRI provides _________contrast resolution which allows for the visualization of structures_______
on conventional radiographs.
improved, unseen
in between patient imagingthe magnet is
still on and personnel are restricted from entering the room
what is sentinel node imaging used for?
imaging a suspected primary metastatic lymph node
What is Nuclear Medicinefusion imaging
combines the functional imaging of nuclear medicine with the anatomic imaging of CT
What is the most common cancer nuclear medicine is us used to treat
Thyroid
now do the nuclear medicine technologist protect themselves radiationduring their daily routine
transport the material in shielded containers
wearing gloves while aspirating and injection radioactive material
placing the radioactive syringe in a special syringe shield
what is the importance of the inverse square law in nuclear medicine?
protects the technologist from the radioactive patient
during PET imaging photons are detected on/by the detector ringby a process called ______ imaging
coincident event
