Final Flashcards by Pirin Pootong

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

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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

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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

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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

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Pixel and Voxel

Field of view (FOV) = diameter of image reconstruction

Pixel size = FOV/matrix size

Voxel = pixel area × slice thickness

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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.

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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

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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

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Positron Emission Tomography

PET provides functional information
CT provides structural information

Key factor: Radiotracer fluorine-18 fluorodeoxyglucose (FDG)

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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

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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

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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.

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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.

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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.

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Imaging

Typically CT is the primary set of images
MRI can be used for soft tissue contouring
PET is less commonly used.

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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

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Early measurement of Radiation

Skin dryness and erythemia
Ulcers formed
Late Effects:
Cataracts
Cancers

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ALARA

As Low As Reasonably Achievable

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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.

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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)

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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

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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

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LD50/60 for Various Species

50% of the irradiated subjects to die w/in 60 days

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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

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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

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 _____.

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.

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 imaging the 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 Medicine fusion 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 radiation during 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 ring by a process called ______ imaging

coincident event