ABR Part 2

How many bytes are in a bit?

0, there are 8 bits in a byte however

What is generally considered to be the limiting MTF value for which an object can be visualized ? 1 0.5 0.2 0.1

0.1

Approximately how much dose is delivered during a planar MV image? 1 R 100 mR 10 R 20 mR

1 R

Modern MRI scanners typically operate in which of the following Magnetic Field strength ranges? 50-200 mT 3-5 T 5-7 T 1-3 T

1-3 T

As per AAPM's code of ethics, promotional items, educational items, or gifts from a business less than what monetary value are acceptable?

100$ monetary value but no gifts in the from of cash or entertainment tickets are ever acceptable.

Which of the following best represent a gigabyte, there may be more than one correct answer 1028 Mb 2^30 bytes 1028 MB 2^20 bytes 2^30 bits 1024 MB 1024 Mb

1024 megabytes (MB) or 2^30 bytes

How much time does a typical CT scan require. Not prep, just the scan itself? 60-70 seconds 90-120 seconds 15-20 seconds

15-20 seconds

When considering an imaging system, which would be preferable for the ADC 16 bit 10 bit 8 bit 12 bit

16 bit, Analog to digital converter would take the greatest bit conversion for finer contrast gradiations which allows better post processing

when representing binary with hexadecimal "digits" make up a byte 4 2 8 16 a hexadecimal digit is larger than a byte

2

The average energy (MeV) of an electron beam can be related to R50 by? 2.33* R50 3*R50 2.50*R50 2*R50

2.33 * R50

Which of the following is a reasonable thorax CT scan dose for an adult? .01 cGy 3 Gy .01 mR 3 cGy

3 cGy or 30 mGy is common

What is an approximate HVL in tissue for the beam provided by a typical diagnostic x-ray tube? 3 cm 15 cm .5 cm 10 cm

3 cm

What's the appropriate value for the gyromagnetic ratio which is used in calculating the Larmor frequency?

42.58 MHz/T for protons

What would be a typical total dose for a pair of photon tangents used for treating breast cancer? 4000 cGy 5000 cGy 6000 cGy 3000 cGy

5000 Cgy

What would be an appropriate total dose for a typical conventionally fractionated lung cancer treatment? 5000 cGy 4000 cGy 3000 cGy 6600 cGy

6600 cGy

Convert the following binary string into hexadecimal 10000101010100000. 8ABF F1A3 EABF 8AA0 D1F4

8AA0, 0000 --> the last four digits are 0 in decimal and hexadecimal form

What % isodose lines is the therapeutic range of electrons?

90-80%

If a film has a high latitude then.. The required time for processing is relatively shorter The film speed is relatively fast A wide Range of input exposures creates a useable range of OD A narrow range of input exposures creates a wide range of OD

A wide range of input exposures creates a useable range of optic densities

Which of the following would be a practical method to increase the QDE of your imaging system? Increasing the mAs Decreasing the image magnification Adding a phosphor screen in front of the imaging device Increasing the kVp

Adding a phosphor screen in front of the imaging device. A phosphor screen would increase counting efficiency and therefore the QDE

What could cause the rise in an MTF curve after it reaches zero? Statistically fluctuation due to low number of photons Aliasing Bug in the analysis software Improper sampling of the phantom

Aliasing, can give the impression that there is a pattern showing when in fact there is not

In hexadecimal which of the following would be equal to 11 11 B F A D

B 1-9 numerals stay the same but 10-15 are represented by letters A-F

How do model-based dose calculation algorithm approaches, such as point kernal approaches, take into account inhomogeneities within a dose calculation volume? By scaling individual kernals with density They don't By activating Monte Carlo techniques when inhomogeneities arise By scaling the calculation volume with effective depths

By scaling individual kernals with density

Which of the following would be most useful for visualizing a patient's prostate? MV planar imaging CBCT MVCT kV planar imaging

CBCT

An Acuros dose calculation can be broken down into four discrete steps which of the following is not one of them? Calculate bremsstrahlung fluence created in patient Transport the fluence from the source model to the patient Perform the dose calculation Calculate the scattered electron fluence in the patient Calculate the scattered photon fluence in the patient

Calculate the bremsstrahlung fluence created in the patient

With reference to your electronic portal imager, which of the following terms is best defined by the following generic description: Signal divided by the mean signal in an image? Quantum Efficiency Quantum Noise Contrast, C Magnification Factor, M

Contrast, it describes how much an object stands out from its surroundings and can be defined, generically, as a signal divided by a mean signal.

What is the difference between Convolution and Superposition?

Convolution can be thought of as the degree of overlap between two functions. Such as between TERMA and the Kernal. Superposition on the other hand, uses density corrections to scale the kernal prior to convolving the TERMA and the density corrected kernal.

When using Monte Carlo in order to increase accuracy and reduce noise, one should increase the number of simulated particle histories. When working with Acuros in order to increase the accuracy one should? Decrease the energy threshold for beginning the CSDA Increase the number of simulated particles Decrease the amount of discretization Increase the calculation grid size

Decrease amount of discretization,

Increasing the kVP of a planar radiograph will lead to what?

Decreased contrast in images.

Why do MV portal images taken on a linac display less contrast than kV images? Increased Pair Production Decreased Photoelectric interactions Need to reduce the patient dose Decreased Compton Scattering

Decreased photoelectric effect

Increasing the gradient in the slice selection direction during an MRI sequence will have the result of? Increasing or decreasing slice thickness?

Decreasing, as gradient is increased for a fixed RF bandwidth the distance the RF frequency range is capable of exciting decreases.

For superficial lesion being treated with electron beams, the collimator size or dimensions of cerrobend blocking should be chosen to match the widest dimension of the lesion. True or False?

False, Isodose levels for low electron beams bulge outward, high isodose lines bulge inward, meaning geometric field edge will not necessarily match Rx isodose curve.

Using a correction factor based on effective depth works just as well as with TPR values as they would with PDD values? True or False?

False, PDD contains an inverse square correction as well as attenuation. Thus this simple effective depth correction will not work with PDD

The distinguishing characteristic between KERMA and TERMA is that KERMA includes the addition of energy released in radiative process such as bremsstrahlung. True or False?

False, TERMA is more inclusive term as it is the TOTAL energy released in matter but both KERMA and TERMA include losses due to radiative processes.

When reviewing a plan calculated with Monte Carlo, one should remember that the absolute error in low dose regions is likely higher than accompanying high dose regions. True or False?

False, absolute error is likely highest in high dose regions of the dose calc. However Relative error in high dose regions will be smaller

In Monte Carlo in order to increase accuracy one simply simulates more histories, but when using Acuros one increases the discretization of the algorithm. True or False?

False, in order to increase accuracy with acuros, one should DECREASE discretization

The repetition time (TR) is the time between an excitation pulse and the 180 degree pulse. True or False?

False, TR is the time between the start of a pulse sequence and its repetition

A chemical shift artifact occurs in an MRI image when the magnetic fields chemically separate charged ions in water regions of the body leading to false contrast in the final image. True or False?

False, chemical shift occurs when protons in different chemical environments excite at different enough frequencies to spatially place them in the wrong voxel. Such as the border of fat and water.

While Cone Beam CT scans may have lower image quality, their scan time is much less than a tradition CT scanner. True or False

False, image quality is reduced and scan time is longer. The Linac gantry spins much slower than a fast x-ray tube in CT.

The Collapsed Cone Convolution dose calculation algorithm speeds up calculation time by ignoring multiple scattering events. the consequence of this is a significant loss in dose calculation accuracy. True or False?

False, it effectively collapses the calculation cone and the algorithm is not affected greatly.

The Anisotropic Analytical Algorithm (AAA) uses Fast Fourier Transform (FFT) to speed up the calculation time. True or False?

False, it uses an Analytical method, which is why analytical is in its name.

During an MRI scan, the loud noises heard are caused by the high levels of RF power moving components of the machine around. True or False?

False, its the gradient coils

Pencil beam dose calculation algorithms for electron beams are particularly accurate at modeling tissue interfaces. True or False?

False, they conceptually are challenged in heterogeneous environments and even more so at material interfaces and oblique incidence.

When writing a journal article, it is appropriate for a graduate student to place their advisor on their paper if the advisor reviews the paper for accuracy after completion and offers feedback. True or False?

False, they must make substantial contributions to the work including data acquisition and interpretation.

Due to the complexities of a modern day treatment, it is expected that small discrepancies in a HU to electron density curve could yield large dosimetric differences in calculated plans. True or False?

False, while very complex, dose distributions vary slowly with HU values

As you increase the number of views in a simple backprojection, eventually a sharp representation of the object will form. true or false?

False, you would need to filter it and do a correction kernal for a sharp image

Which term below belongs to this definition regarding flat panel portal imagers: This term is the ratio of the collecting (sensitive) area to the electronics. Pixel Density Quantum detection Portal efficiency Fill Factor

Fill Factor --> represents the amount of the flat panel detector that is sensitive to incident radiation

The health law enacted in 1996 governing the protection and distribution of private health information was termed what?

HIPAA Health Insurance Portability and Accountability Act

In order to speed up Monte Carlo algorithms Variance Reduction Techniques are employed. Which of the following is not a Variance Reduction Technique used? Range Rejection Russian Roulette Condensed Histories History Rejection Splitting

History Rejection

Which of the following options would have the potential to reduce the slice thickness of a spin-echo sequence? Increase MR gradient Decrease slice select RF bandwidth Decrease MR gradient Increase slice select RF bandwidth

Increase MR gradient and Decrease slice select RF bandwidth

The mathematical equation describing the macroscopic behavior of radiation traveling through matter that is utilized by Monte Carlo and Acuros calculation algorithm is termed the __________?

Linear Boltzmann transport equation

In order to maintain a state of superconductivity inside an MRI unit, the coils are cooled using what? Liquid Helium Liquid Hydrogen Liquid Oxygen Liquid Nitrogen

Liquid Helium which liquifies around 3 Kelvin and easily maintains a state of superconductivity

Which of the following TE and TR values would you use to produce a proton density weighted image? Long TR Long TE Short TE Short TR

Long TR and Short TE will suppress both T1 and T2 differences

If the reconstructed slice thickness of a CT unit were to be increased from 1.25 mm to 5 mm, what would be the consequence to image quality? Low contrast resolution would improve The time for scanning will increase High contrast resolution would improve Image noise will increase

Low contrast resolution would improve

Which type of media is commonly used for cheap long term storage that does not need frequent access? Solid state disk magnetic tape microfiche magnetic disk optical disk

Magnetic Tape, frequently used as cheap long term storage option but due to its slow speed cannot practically be used for data thats typically needed, so it's used as backup media.

what portion of an H&D curve would you expect to obtain significant contrast between different tissue types?? Shoulder, Toe, or Middle

Middle

Which of the following options of dose calculation algorithm types would best be able to account for curved MLC leaf ends? Correction Based Model Based

Model-Based Dose Computation, correction based allow for corrections for such characteristics as tissue heterogeneities, surface contours, and beam modifiers while model based take accuracy one step further and allow for corrections to curved leaf ends, tongue and groove effect, leaf transmission, electron contamination, tissue heterogeneities etc.

Which treatment planning system ha a greater stochastic error and which has a greater deterministic error? Monte Carlo and AcurosXB

Monte Carlo has greater Stochastic error Acuros has greater Deterministic error

In consideration of treatment planning with electrons, which of the following options would provide the most reliable method for dose calculation? Pencil Beam algorithms Algorithms based on measured beam date Monte Carlo

Monte Carlo, measured beam data loses a great deal of accuracy outside of the water phantom and pencil beam is adequate enough to indicate effects.

On an H&D curve, where would you expect the highest speed films to be?

Near the left side, where optic density increases at a higher slope

Will a calculation algorithm utilizing correction factors based on effective depths tend to overestimate or underestimate the dose in lung at 6 MV?

Overestimate, this can be attributed to this correction factor not accurately taking account scattered radiation which contributes with primary radiation to the dose at a point within the inhomogeneous medium.

Which of the following is not recommended as daily quality assurance of a portal imager in the AAPM's Tast Group 58 on the clinical use of electronic portal imaging? Verify Image Quality Verify Data Capacity Test Collision interlock Perform Mechanical Inspection

Perform Mechanical Inspection

Which of the following setups would yield the lowest imaging dose to the patient while still maintaining an acceptable image? A phosphor screen in front of the film A bare film with no phosphor screen A phosphor screen behind the film Phosphor screens in front of and behind the film

Phosphor screens in front of and behind the film

You perform a measurement using your brand new CT simulator and find that, at 100 kVp, that measured HU of hard bone is 25% higher than the HU of the same material scanned at 140 kVp. What represents the most likely culprit? Photoelectric effect mA Scatter The timing resolution of the scan

Photoelectric effect

Based on your knowledge of kernals, which of the following options, conceptually is more accurate? Point Kernal Pencil Beam Kernal

Point Kernal, pencil kernal is idealized in that we consider the interactions emanating from a so-called pencil beam whereas point kernals break this down one step further by defining each kernal as a single photon interaction at a point.

In an MRI image, if everything is bright except for bone, what MRI sequence would you expect it to be? T1 T2 FLAIR Proton Density Weighted

Proton Density Weighted

through what mechanism does the grid placed in front of an image detector improve the x-ray image quality? Removes beam divergence Provides buildup for x-ray beam Increases effective energy of the beam Removes scattered component

Removes scattered component

Low contrast object detection using portal imaging with megavoltage photons is due mostly to : Scatter SNR Photon source size Active Imager dimensions

SNR --> maximizing the SNR is key to discerning low contrast objects

Select which of the following TE and TR values you would use for a T1 weighted image Long TE Long TR Short TR Short TE

Short TE and Short TR as short TR enhances T1 differences while short TE suppresses T2 differences

When increasing the number of simulated histories on a particle in a Monte Carlo based dose calculation approach, which of the following options best describes how the isodose lines will change? The isodose lines will shrink The isodose lines will appear smoother The isodose lines will increase in magnitude The isodose lines will appear more jagged

Smoother, the reason for this qualitative change is because you are effectively increasing the statistical nature of the calculation

Which of the following represents the greatest advantage received from performing an FFT in place of a brute force convolution? Speed Dosimetric Accuracy Wider Kernals Spatial Accuracy

Speed, the fast fourier transform provides a great advantage in making computational heft of the convolution a bit less bulky

A Monte Carlo calculation yielding the deposition of energy in an absorbing medium for an individual photon is an example of: A deterministic process A stochastic process Cannot be determined

Stochastic process, an interaction of an individual photon is random in nature and, therefore, fits the definition of stochastic

The term Anisotropy refers to? A large degree of symmetry being present Symmetry not being present Atoms that are not isotopes A method for computers to discretize continuous functions

Symmetry not being present, It represents inhomogeneity

T1 or T2 relaxation occurs when protons re-align with the magnetic field causing a regrowth of the bulk magnetization vector?

T1

Imperfections in the magnetic environment causing a decay of magnetization is represented by T2 decay T1 decay Proton Density decay Spin Echo

T1 decay

T2 or T1 relaxation is caused by a dephasing of the transverse components of proton dipoles ?

T2

Perhaps the most important concept for calculating dose on a computer system is Dose = ____________ x (convolution) Kernal fill in the blank.

TERMA

Whats the proper equation for calculating specificity of a diagnostic test?

TN/(TN+FP) --> specificity relates to how accurately you can predict negative test results

Which of the following options is information that can be derived from a standard H&D curve? Processing time required to produce a film How thick a film's phosphor screen is The Amount of Optic Density that is due to base plus fog How energetic the X-rays used to make the film are

The amount of OD that is due to base plus fog

Directly solving the Botlzmann Transport Equation requires that Acuros discretize some parameters. Which of the following is not a parameter Acuros discretizes? Space Energy Time Angle

Time

A CT uses ionizing radiation. True or False?

True

A unique feature of MRI imagers is that they can reconstruct a series of slices in any arbitrary plane (not just axial, sagittal, and coronal planes). True or False

True

Electron Monte Carlo requires much tighter modelling of the LINAC head than photon Monte Carlo. True or False?

True

For best image quality, an MRI scan requires the patient to don a receiver coil specific to the site being imaged? True or False?

True

In the absolute limit of their respective accuracies, both Monte Carlo and Acuros should yield the same answer. True or False?

True

The Linear Boltzmann Transport Equation used in both Monte Carlo and Acuros assumes that there are no external magnetic fields present and that particles do not interact with each other. True or False?

True

The exact HU value of an object may vary substantially depending on the kVp a CT scan is obtained with. True or False?

True

the Nyquist frequency is the minimum sampling frequency required for visualization of an object. True or False?

True

the location of an object within a phantom will have an effect on the measured HU value. True or False?

True because the effective energy of the beam changes with location in the phantom

As opposed to many other algorithms, which utilize electron density calibration curves to calculate dose, both Monte Carlo and Acuros requires mass density for dose calculation. True or False?

True, first step of both is taking HU values from planning CT and assigning them with mass density

Which of the following options would be the best way to reduce noise in a CT scan? Decrease the kV Decrease the slice thicknes Increase the pitch Use a smoothing reconstruction algorithm

Use a smoothing reconstruction algorithm

A patient with solitary lung metastases is referred for surgery by a medical oncologist. During the consult, the patient is given risks and rationale for surgery who then signs a consent. After undergoing surgery, they find out they were eligible for stereotactic radiosurgery and could have avoided the surgery. Can the surgeon get sued?

Yes, the patient has a right to INFORMED consent. They were not apprised of all treatment options.

Which items will appear darker in a CT than an object that has a CT number of -10 air, lung, spongy bone, striated muscle, water

air and lung

When considering Monte Carlo, a single incident particle and all its descendants is termed a _______?

history

The number of scattered photons that are recorded by an x-ray film can be decreased by... decreasing the beam filtration decreasing the source to object distance decreasing the object to detector distance increasing the grid ratio

increasing the grid ratio

What does a FLAIR sequence do in MRI

it removes all signal from fluids

Which imaging modality listed would have the largest scatter fraction ( the fraction of the total fluence reaching the image receptor that is due to scattered x-rays)? Assume scatter grids are not used. kV x-ray imaging mV portal imaging

kV imaging has a greater scatter fraction vs MV, TG 58 cites that the scatter fraction decreases from .9 at 100 keV to less than .6 at 6MV

In a Planar radiography, what does a larger focal spot typically mean?

lower effective resolution due to geometric blurring. Also means you may have higher mA, as mA is increased, often it requires a larger focal spot

Partial Volume artifacts for CT images can be reduced by decreasing ________ image matrix, kVp, section thickness, or acquisition time ?

section thickness

How can you identify a T2 weighted MRI?

water substance will show bright, such as CSF but bone and white matter will look dark. Easy to look at the eyes, they should be a bright white

In a Catphan, what color would the insert be if it were representing bone?

white