PARP 2022 Flashcards
What is the most widely used anode material in diagnostic radiography due to its high melting point and atomic number? (Bushberg, et al., p. 180)
Tungsten
Chapter 6.2
Diagnostic radiology: Tungsten (better resistance if with rhenium)
Mammography: Mo, Rh
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Cobalt’s relevance
COBALT
Principally used as a uniform flood field source for scintillation camera quality control in nuclear medicine
Which of the following refers to the measure of the average amount of energy deposited locally (near the incident particle track) in the absorber per unit path length? (Bushberg, et al., p. 36)
Linear energy transfer
Chapter 3.1
Unit: keV or eV per μm
The LET of a charged particle is proportional to the square of the charge and inversely proportional to the particle’s kinetic energy
In general, for a given absorbed dose, the dense ionization tracks of “high LET” radiations (alpha particles, protons, etc.) deposit their energy over a much shorter range and are much more damaging to cells than the spare ionization pattern associated with “low LET” radiations.
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Exposure
-The amount of electrical charge (Q) produced by ionizing electromagnetic radiation per mass (m) of air is called exposure (X)
-Historical unit: roentgen (abbreviated R)
-The output intensity of an x-ray machine can be measured and expressed as an exposure (R) per unit of current times exposure duration (milliampere second or mAs) under specified operating conditions (e.g., 5 mR/mAs at 70 kV for a source-image distance of 100 cm, and with an x-ray beam filtration equivalent to 2 mm Al)
Imparted energy
-The total amount of energy deposited in matter, called the imparted energy, is the product of the dose and the mass over which the energy is imparted. The unit of imparted energy is the joule
Absorbed dose
-The quantity absorbed dose (D) is defined as the energy (E) imparted by ionizing radiation per unit mass of irradiated material (m)
-Absorbed dose is defined for all types of ionizing radiation (i.e., directly and indirectly ionizing).
-The SI unit of absorbed dose and kerma: Gy
-Older unit: Rad (an acronym for radiation absorbed dose)
1 rad = 10 Gy
-If the energy imparted to charged particles is deposited locally and the bremsstrahl- ung produced by the energetic electrons is negligible, the absorbed dose will be equal to the kerma.
What refers to the reduction in x-ray beam intensity towards the anode side of the x-ray field? (Bushberg, et al., p. 184)
Heel effect
Chapter 6.2
The heel effect is less prominent with a longer source-to-image distance (SID)
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Inherent filtration effect
-Filtration is the removal of x-rays as the beam passes through a layer of material
-Includes: inherent filtration of the x-ray tube vs added filtration
-Inherent filtration includes the thickness (1 to 2 mm) of the glass or metal insert at the x-ray tube port.
Glass (primarily silicon dioxide, SiO2) and aluminum have similar attenuation properties (ZSi = 14 and ZAl = 13) and effectively attenuate all x-rays in the spectrum below about 15 keV. Dedicated mammography tubes, on the other hand, require beryllium (Z = 4) to permit the transmission of low- energy x-rays. Inherent filtration includes attenuation by housing oil and the field light mirror in the collimator assembly.
Added filter:
-Al: most common
Bremsstrahlung effect
-The radiation emission accompanying electron deceleration is called bremsstrahl- ung, a German word meaning “braking radiation”. The deceleration of the high-speed electrons in an x-ray tube produces the bremsstrahlung x-rays used in diagnostic imaging.
Nyquist effect
-Nyquist frequency sets the upper bound on the spatial frequency that can be detected for a digital detector system with detector pitch delta
-If a sinusoidal signal greater than the Nyquist frequency were to be incident upon the detector system, its true frequency would not be recorded, but rather it would be aliased. Aliasing occurs when frequencies higher than the Nyquist frequency are imaged. The frequency that is recorded is lower than the incident frequency, and indeed the recorded frequency wraps around the Nyquist frequency.
Which of the following is a GOOD RECOMMENDATION to maximize x-ray tube life? (Bushberg, et al., p. 189):
a. Use higher tube current with shorter exposure times to achieve the desired mAs
b. Always do extended or repeated operation of the x-ray tube with high technique factors
c. Maximize filament boost “prep” time
d. Limit rotor start and stop operations
d. Limit rotor start and stop operations
Chapter 6.2
a. Use LOWER tube current with LONGER exposure time to achieve the desired mAs
b. AVOID extended or repeated operation of the x-ray tube with high technique (kV and mAs) factors because, even though the x-ray generator has logic to prohibit single exposure settings that could damage the x-ray tube, multiple exposures could etch the focal track, resulting in less radiation output; transmit excessive heat to the bearings; and cause outgassing of the anode structure that will cause the tube to become unstable
c. Minimize filament boost “prep” time (the first detent of two on the x-ray exposure switch) especially when high mA is used. If applied for too long, filament life will be shortened, unstable operation will occur, and evaporated tungsten will be deposited on the glass envelope
d. True
X-ray quality refers to the penetrability of an x-ray beam and depends on the following factors, EXCEPT: (Bushberg, et al., pp. 202-206)
a. kV
b. mAs
c. Tube filtration
d. Generator waveform
b. mAs
Chapter 6.5
Quality describes the penetrability of an x-ray beam, with higher energy x-ray photons having a larger half-value layer (HVL) and higher “quality.”
Quantity refers to the number of photons comprising the beam.
Exposure is nearly proportional to the energy fluence of the x-ray beam.
**Tube voltage (kV) ** determines the maximum energy in the bremsstrahlung spectrum and affects the quality of the output spectrum. In addition, the efficiency of x-ray production is directly related to tube voltage. Exposure is approximately proportional to the square of the kV in the diagnostic energy range.
An increase in kV increases the efficiency of x-ray production and the quantity and quality of the x-ray beam.
Changes in the kV must be compensated by corresponding changes in mAs to maintain the same exposure.
Tube current (mA) is proportional to the number of electrons flowing from the cathode to the anode per unit time. The exposure of the beam for a given kV and filtration is proportional to the tube current. Also the exposure time is the duration of x-ray production. The quantity of x-rays is directly proportional to the product of tube current and exposure time (mAs)
Generator waveform affects the quality of the emitted x-ray spectrum. Both the quality and quantity of the x-ray spectrum are affected
Beam filtration modifies the quantity and quality of the x-ray beam by preferentially removing the low-energy photons in the spectrum. This reduces the number of photons (quantity) and increases the average energy, also increasing the quality.
In screen film radiography, what refers to the protrusion of the positive charge that reaches the surface of the silver halide crystal, caused by lattice defects in AgS? (Bushberg, et al., p. 211)
Sensitivity speck
Chapter 7.2
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Developer p211
The gelatin layer is permeable to aqueous solutions, which is necessary for the aqueous developing chemicals to come into contact with the silver crystals. When the film is developed in an aqueous chemical bath containing a reducing agent, called the developer, the metallic Ag atoms at the latent image centers act as a catalyst, causing the remaining silver ions in that grain to be reduced. A grain of reduced metallic silver atoms appears as a black speck on the film.
Latent image center
When a silver halide grain is exposed to visible light, a small number of Ag ions are reduced (gain electrons) and are converted into metallic Ag (Ag e → Ag). If 5 Ag ions are reduced, which depends on the incident light intensity, a stable latent image center is formed.
Fixer
After the film has passed through the developer, it passes through a bath of an aque- ous oxidizing solution called fixer that dissolves the remaining (inactivated) silver halide from the emulsion layer areas that were not exposed (or were underexposed) to light. The film is then rinsed with water to remove residual developer and fixer, and is dried.
What is the predominant interaction of x-ray and gamma ray photons in the diagnostic energy range? (Bushberg, et al., p. 38)
Compton scattering
Chapter 3.2
**Rayleigh scattering = Rayleigh is classic and coherent
**
-Photon interacting with the whole atom
-Occurs mainly with very low energy x-rays, such as those used in mammography (15 to 30 keV)
-Ionization DOES not occur
-In medical imaging, detection of the scattered x-ray will have a deleterious effect on image quality.
-In general, the average scattering angle decreases as the x-ray energy increases
**Compton scattering = Inelastic and nonclassical
**
-Most likely to occur between photons and outer (“valence”)-shell electrons
-Ionization OCCURS
-In x-ray transmission imaging and nuclear emission imaging, the detec- tion of scattered photons by the image receptors results in a degradation of image contrast and an increase in random noise
-The relative probability of a Compton interaction increases, compared to Rayleigh scattering or photoelectric absorption, as the incident photon energy increases.
-The probability of Compton interaction also depends on the electron density (number of electrons/g 3 density).
With the exception of hydrogen, the total number of electrons/g is fairly constant in tissue; thus, the probability of Compton scattering per unit mass is nearly independent of Z, and the probability of Compton scattering per unit volume is approximately proportional to the density of the material.
Average glandular dose
The glandular tissue is the site of carcinogenesis, and thus the preferred dose index is the average glandular dose.
Average glandular dose per cranio-caudal projections:
1 mGy (without grid)
3 mGy (with grid)
Midbreast dose
The midbreast dose, the dose delivered to the plane of tissue in the middle of the breast, was the radiation dosimetry benchmark until the late 1970s. The midbreast dose is typically lower than the average glandular dose and does not account for variation in breast tissue composition.
Luis-senpai, being the stellar senior that he is, was teaching the rotators, Aimah and Mac, how to perform a double-contrast barium enema. After telling our awesome radtech Ma’am Susan to “fluoro off po”, Aimah noted that the last acquired image is displayed in the monitor instead of a blank screen. Mac asked Luis-senpai why the monitor is showing that image, for which Luis-senpai confidently replied, “Ah, hihi, ganyan talaga ‘yan, for dose reduction kasi ‘yan, at ang tawag sa ganyan ay: ____” (Bushberg, et al., p. 297)
Last-frame-hold
Chapter 9.5
Road mapping
Road mapping is a software- and video-enhanced variant of the last-frame-hold feature and is useful for angiography procedures. Two different approaches to road mapping can be found on fluoroscopic systems. Some systems employ side-by-side video monitors, and allow the fluoroscopist to capture an image (usually with a small volume of injected contrast media), which is then shown on the monitor next to the live fluoroscopy monitor. In this way, the path of the vessel can be seen on one monitor, while the angiographer advances the catheter viewing in real-time on the other monitor. Another approach to road mapping is to capture a contrast injec- tion image or subtracted image, and use this as an overlay onto the live fluoroscopy monitor. In this way, the angiographer has the vascular “road map” superimposed on the fluoroscopy image and can orient the guidewire or catheter tip to negotiate the patient’s vascular anatomy. Road mapping is useful for advancing catheters through tortuous vessels.
Frame averaging
Fluoroscopy systems provide excellent temporal resolution, a feature that is the basis of their clinical utility. However, fluoroscopy images are also relatively noisy, and under certain circumstances it is appropriate and beneficial to (reduce) temporal resolution for lower quantum noise. This can be accomplished by averaging a series of images, as shown in Figure 9-11. Appreciable frame averaging can cause noticeable image lag with reduced temporal resolution. Aggressive use of frame averaging can provide lower dose imaging in many circumstances.
Which of the following refers to the product of the absorbed dose and radiation weighting factor? (Bushberg, et al., p. 56)
Equivalent dose
Chapter 3.3
Equivalent dose
-Not all types of ionizing radiation cause the same biological damage per unit absorbed dose. To modify the dose to reflect the relative effectiveness of the type of radiation in producing biologic damage, a radiation weighting factor (wR) was established by the ICRP as part of an overall system for radiation protection
-The product of the absorbed dose (D) and the radiation weighing factor is the equivalent dose (H).
-The SI unit for equivalent dose is joule per kilogram with the special name of the sievert (Sv), where 1 Sv 5 1 J kg21.
Dose equivalent
It is the product of the absorbed dose and the quality factor (Q) (Equation 3-24). The quality factor is similar to wR.
The traditional unit for both the dose equivalent and the equivalent dose is the rem. A sievert is equal to 100 rem, and 1 rem is equal to 10 mSv.
Effective dose
-A measure of equivalent dose, weighted for the bio- logical sensitivity of the exposed tissues and organs (relative to whole body exposure) to stochastic health effects in humans
-The sum of the products of the equivalent dose to each organ or tissue irradiated (HT) and the corresponding weighting factor (wT) for that organ or tissue is called the effective dose (E).
Kerma
Kinetic energy transferred to charged particles per unit mass
The component of the ultrasound transducer that converts electrical energy to mechanical energy is the: ____. (Bushberg, et al., p. 513)
Piezoelectric material
