Mixed Review Deck 4 Flashcards by Jessica Vigorito

The annual occupational dose limit is valid for what radiations?

Beta, x and gamma

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Why are alpha particles practically harmless as an external source of radiation?

They can only travel a few centimeters in air

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Who can determine if a patient needs oxygen?

Only a physician bc it is considered a drug.

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What is the unit for spatial frequency?

Lp/mm

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When determining lp/mm with a given pixel size, how wide is the smallest line on the image? How many pixels make a line pair?

Line is 1 pixel wide
2 pixels make a line pair

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Device that monitors the luminance response and uniformity of monitors used in digital imaging?

Photometer. There are 2 types, near-range and telescopic.

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In amorphous selenium FPDs, the term amorphous means…

A crystalline material lacking its typical crystalline structure

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A capacitor discharge mobile unit is a/k/a…

A condenser discharge unit

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What is the major advantage and the major disadvantage of a capacitor discharge mobile unit?

Advantage is its light weight due to carrying no batteries so it needs no motor to drive or brake.

Disadvantage is as capacitor discharges its charge, kV decreases throughout exposure, so it must be charged between exposures.

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Capacitor discharge units use capacitors to power the…

Xray tube only (no motor needed to drive it)

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To compensate for variations in gain across a digital receptor, what maintenance steps should be taken?

Conduct a calibration correction for image nonuniformity.

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A test pattern, such as the TG 18-CT test pattern, is used to qualitatively evaluate

The luminance response of a digital display monitor

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A spinning top test should show ___ dots for every _____ in the generator’s waveform.

1 dot per pulse. So if the generator should be producing a waveform with 60 pulses per second, in 1 second the test should show 60 dots.

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Give the number of pulses pet second produced by a ..

Single phase generator, half wave rectified
Single phase, full wave rectified
3 phase, half wave rectified
3 phase, full wave rectified

Single phase, half wave rectified: 60 pps
Single phase, full wave rectified, 120 pps

3 phase, half wave rectified: 180 pps
3 phase, full wave rectified: 360 pps

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Which projection should be performed and evaluated before performing a Settegast projection for trauma?

Lateral patella to rule out a transverse fracture

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The xray unit of exposure defines…

Air kerma

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SI unit describing dose to biologic material

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A fractional focus tube will have a focal spot size of ___ or smaller and is used in ______ radiography to maintain ______.

0.3 mm, magnification, image sharpness

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What is the effect of a deeper focusing cup on actual focal spot size?

Keep electron cloud confined more effectively (smaller actual focal spot)

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Dysplasia refers to

Abnormal development of tissue

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Roadmapping in fluoro …

Keeps most recent fluoroscopic imsge on screen
Aids in placement of guidewires and catheters
Reduces need for continuous xray exposure to the patient

All 3

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A 4 diode rectifier in diamond shape produces _____ rectification.

Full wave

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An inverter is part of what type of xray generator?

High frequency

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Define a sentinel event

A fluoroscopic skin dose of greater than 15 Gy. This must be reported to the Center for Devices and Radiological Health (CDRH)

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Leakage radiation (per NCRP 102) must not exceed...

1 mGy(air) per hour at 1 m from the tube

As the anode target angle increases... Effective focal spot size _____ Spatial resolution ____ Anode heat capacity _____

Effective FSS increases Spatial resolution decreases Anode heat capacity is unchanged bc actual FSS is unchanged

For a scapula y lateral shoulder, the humeral head should sit...

Superimposed over the y junction formed by the acromion and coracoid process

3 essential criteria for xray production

Source of electrons Means to accelerate electrons Target material capable of causing the electrons to decelerate

A tube placed into a cavity to introduce or withdraw material

Cannula

Adult orthoentgenography is radiographic measurement of... And requires how many exposures?

Measurement of long bones of lower extremity 3 exposures: hip, knee and ankle

In the CR reader, some of the laser light is redirected to a reference detector by way of... In order to...

A beam splitter To monitor laser beam intensity to adjust for any fluctuations

Define each, and which are most and least radiosensitive? Myelocyte Myocyte Erythroblast Megakaryocyte

Myelocyte is a wbc precursor Myocyte is a mature muscle cell Erythroblast is a rbc precursor Megakaryocyte is a platelet precursor Least radiosensitive: myocyte Most radiosensitive: erythroblast

How long is each portion of the small intestine?

Ileum, 6 to 12 feet Jejunum, 3 to 6 ft Duodenum, about 10 inches

Acute abdomen series includes

AP erect (or L lateral decubitus) AP recumbent PA chest (erect)

What's in a 3 way abdomen study

AP recumbent AP erect L lateral decubitus

Best position to see anterior and posterior aspects of stomach and retrogastric space?

Lateral recumbent (usually R lateral)

Peristaltic activity is greatest in this position, so it's best to demonstrate the stomach's emptying mechanism.

RAO (prone)

Best position/projection of sigmoid colon

PA axial; prone; CR 35 degrees caudal to midline at ASIS level

Best position for opening the ascending colon and hepatic flexure

RAO (or LPO)

Kidneys lie at what vertebral levels

T 12 to L3

Ureteral filling of contrast is best viewed in what position and projection?

PA/prone

Define free radical

Atom with unpaired electrons, short lived but highly reactive, can travel from its source and break chemical bonds in order to pair with another electron

Dynamic range

Range of exposures that can be captured by a detector

Current flowing thru a coil of wire? What's it called if you add a ferromagnetic core?

Solenoid Electromagnet

Voltage ripple associated with a 3 phase 12 pulse rectified generator in pulses per half cycle

3 pulses per half cycle

If 1 rectifier were malfunctioning, the resulting mAs would be...

Half that expected

Switching from single phase to 3 phase equipment, how to adjust kVp?

Reduce by 12%

Radiologic imaging uses ___ ___ computer processing

Real time

Principle reason for image integration in digital fluoroscopy

Improves contrast resolution

Most common cause of x-ray tube failure

Vaporized tungsten on glass envelope

Minimum acceptable TV SNR in digital fluoroscopy

1000:1

The mask image in subtraction imaging is usually the...

Image just preceding contrast injection

Interrogation time

In digital imaging, time it takes to switch on the xray tube

If an xray produced using AEC is overexposed bc required exposure is shorter than the minimum response time you should...

Decrease mA

Flux gain measures increase in ___ due to conversion efficiency of the ____

Light photons Output screen/phosphor (due to increased kinetic energy of the electrons)

Define minification gain and it's formula

Increase in brightness or intensity due to number of electrons at the input screen being compressed to a small output screen INPUT DIAMETER^2 / OUTPUT DIAMETER ^ 2

Part of II tube responsible for the liberation of electrons which are then accelerated toward the anode disc

Photocathode

Name for the process of converting xray and light energies into electrons from a photocathode surface

Photoemission

What's the voltage difference (potential difference) between the photocathode and anode in most image intensifiers?

25,000 to 30,000 V

The input phosphor is composed of

Cesium iodide

The photocathode is made of

A cesium antimony compound

The output phosphor is made of

Zinc cadmium sulfide

Formula for total brightness gain

Flux gain X minification gain

Formula for Flux gain

# of light photons at output / # of xrays at input

The photocathode converts..

Visible light to electrons

To maintain brightness gain, a decrease in Flux gain would require...

An increase in minification gain

Why are the II input phosphor and the photocathode both concave in shape?

Reduce distortion (travel distance between photocathode and output phosphor is exactly equal for electrons)

The photocathode and input phosphor are ___ in shape

Concave

Continuous fluoro exposes at a rate of ___ frames per second

In mag mode... A. Why is minification gain decreased? 2. What compensates for the loss in brightness gain?

A. Less photoemission from the photocathode due to less input diameter B. Increase Flux gain by increasing kV or mA

Magnification with multifield image intensification is accomplished by shifting the electron stream focal point forward... how?

Place a stronger negative charge on the electrostatic focusing lenses

Annual effective dose per person FROM NATURAL BACKGROUND radiation is approx...

3.0 mSv

An acute dose of ____ is required to produce cataracts (Or an occupational/fractionated dose of ___ Gy)

2 Gy acute 10 Gy fractionated

Threshold dose for lymphocyte depletion

0.25 Gy

Positive beam limitation must be accurate within ___ % of SID for a single side and within ____ % of SID for all sides

3% and 4%

Threshold doses for each of the 3 forms of ARS

Hematopoietic: .7 to 10 Gy GI: 10 to 100 Gy CV or CNS 50 Gy

What is SED(50) for humans

*dose required to produce erythema in 50% of population Humans: 5 Gy

How is oxygen enhancement ratio of cells or tissue determined

Dose required to cause effect without oxygen / dose required to cause that effect with oxygen

When during the cell cycle are cells most radiosensitive?

Gap 2 of interphase and mitosis (M)

Divisions of interphase and when are cells least radiosensitive?

Gap 1, S (synthesis) and Gap 2 Synthesis (DNA replication), least radiosensitive

Give radiation weighting factors for... X and gamma rays Protons Slow neutrons Fast neutrons Alpha particles

X/gamma rays 1 Protons 2 Slow neutrons 10 Fast neutrons 20 Alpha 20

1 angstrom is

10 ^ -10 m

Wavelength of diagnostic xrays

10^-8 to 10^-12 m

All electromagnetic radiations travel at what speed

Speed of light, 3 x 10^8 meters/sec Or 186,000 miles/s

Length of latent period of ARS is inversely related to ...

Amount of exposure received

Annual US background radiation exposure 1 CXR dose Whole body CT dose

6 mSv 0.10 mSv 10 mSv

Dose response curve that predicts deterministic effects

Nonlinear threshold

Effects whose probability but not severity is dose dependent

Stochastic