Initial Certification for Medical Physics

New Question Types: Parts 1 and 2

Last verified on August 21, 2017
New question types for the medical physics Part 1 and Part 2 exams are expected to add flexibility to assessing the knowledge of candidates seeking and maintaining certification. Beginning with the 2017 exams, new question types will appear incrementally, and they will be evaluated by psychometric analysis to validate appropriate performance and other important exam criteria. To ensure a fair and equitable exam process, adjustments and fine-tuning of exam parameters (e.g., time allotted for different question types) will be ongoing.
The majority of all exam content will continue to be the multiple-choice question with a single best answer, with a small fraction of each new question type being present in future exams.

Explanation and Examples of New Questions Types

Case-based questions, which are targeted to eventually replace the complex question type, consist of two or more (typically three) sequentially related questions on a single topic. Each question in a case-based group is a single-answer, multiple-choice question and makes up a single scorable unit. The questions are linked in a one-way direction that does not allow going back to change an answer after moving to the next question. Often, the correct answer to the previous question will be part of the next question, giving an opportunity for testing knowledge with more granularity.
Therefore, instead of the possibility of only zero or three scorable units for a complex question, candidates will have an opportunity to receive credit for zero, one, two, or three scorable units in a case-based group. Case-based questions will be clearly identified for the examinee, with instructions and warnings stating that after the first question is answered, each subsequent question must be completed, and that there are no opportunities to change a response once recorded. The implementation plan is to gradually replace the 25 complex questions now in the Part I general and Part 2 discipline-specific certification exams with case-based questions having a similar number of scorable units.
Example of a complex question changed to a case-based question group
MRI resonance frequency and chemical shift concepts, complex question (3 scorable units):
An MR image is acquired with a gradient strength of 2.5 mT/m over a field of view of 25 cm and 128 frequency-encoding samples. If fat and water are shifted in an MR image by exactly 1 pixel, what is the main magnetic field strength? (Assume that the chemical shift of fat to water is 3 ppm.)
  1. 0.8 T
  2. 1.0 T
  3. 1.3 T
  4. 1.6 T
  5. 3.0 T
Answer: D (Follow the case-based questions below to arrive at the answer.)
Case-based question group revised from the complex question
MRI resonance frequency and chemical shift concepts (3 parts, single scorable unit per question):
Part 1. An MR image is acquired with a gradient strength of 2.5 mT/m over a field of view of 25 cm during the Frequency Encode Gradient readout. What is the bandwidth of the echo?
  1. 62.5 kHz
  2. 48.8 kHz
  3. 31.3 kHz
  4. 26.6 kHz
  5. 14.7 kHz
Answer: D
2.5 mT/m*0.25m = 0.625 mT BW = 0.625 mT/1000 mT/T * 42.58 MHz/T = 0.0266 MHz = 26.6 kHz
BLOCK
Part 2. If the 26.6 kHz bandwidth echo is acquired with 128 samples in the frequency-encoding direction of the k-space matrix, what is the bandwidth across each pixel?
  1. 208 Hz
  2. 230 Hz
  3. 381 Hz
  4. 416 Hz
  5. 652 Hz
Answer: A
BW across each pixel is 26.6 kHz / 128 samples = 208 Hz
BLOCK
Part 3. If fat and water are shifted in the MR image by exactly 1 pixel, what is the main magnetic field strength? (Assume the chemical shift of fat to water is 3 ppm.)
  1. 1.0 T
  2. 1.2 T
  3. 1.4 T
  4. 1.6 T
  5. 1.8 T
Answer: D
Chemical shift = 208 Hz, which is 3 ppm of the resonance frequency of the main magnet. Use this information to get the estimated field strength: 208 Hz / 3 × 10-6 = 69.3 MHz Magnet strength = 69.3 MHz / 42.58 MHz/T = 1.62 T
All subsequent interactions with these questions are blocked within the exam.
Multiple-select question types are a variant of multiple-choice questions with a single best answer. They have multiple correct answers (typically two or three) and multiple incorrect answers (distractors) for a single scorable unit. These questions specifically state the exact number of responses required to identify the correct answers. To receive credit for a single scorable unit for the question, an exact match of the responses with the correct answers is necessary. Choosing an incorrect answer will result in no credit.
In addition, failure to provide the exact number of required correct responses results in no credit for the question. Multiple-select questions add flexibility to assess knowledge when there is more than one good answer and can largely replace questions that use negative stems (e.g., “Which of the following is NOT,” “All of the following are correct outcomes EXCEPT”), which are less desirable from an exam psychometrics perspective.
Non-physics example of a multiple-select question
Which three of the following cities are state capitals? (Please select 3 options.)
  1. Columbus
  2. Lexington
  3. Minneapolis
  4. New York City
  5. Sacramento
  6. St. Louis
  7. Tallahassee
Answer: A, E, and G; to receive credit, all three of these options must be selected.
Diagnostic medical physics example of a multiple-select question
During a fluoroscopy procedure with automatic exposure rate control (AERC), an additional 0.1-mm Cu filter is added to the inherent filtration. Select the three changes that occur to the kV, mA, and patient air-kerma rate when the AERC stabilizes. (Please select 3 options.)
  1. kV increases
  2. kV decreases
  3. mA increases
  4. mA decreases
  5. Air kerma rate increases
  6. Air kerma rate decreases
Answer: A, C, and F; to receive credit, all three of these options must be selected. In this question, note that there are three separate comparisons (kV, mA, and air kerma rate).
Nuclear medical physics example of a multiple-select question
Which three of the following affect parallel-hole collimator resolution? (Please select 3 options.)
  1. Hole length
  2. Hole diameter
  3. Field of view
  4. Source distance
  5. Focal length
  6. Pinhole diameter
Answer: A, B, and D; to receive credit, all three of these options must be selected.
Therapeutic medical physics example of a multiple-select question
For an electron beam, as the field size decreases, which three of the following occur? (Please select three options.)
  1. The depth of Dmax decreases.
  2. The depth of Dmax increases.
  3. Surface dose increases.
  4. Average energy increases.
  5. Practical range decreases.
  6. For field size > Rp, the PDD remains unchanged.
Answer: A, C, and F; to receive credit, all three of these options must be selected.
Fill-in-the-blank question types require the candidate to answer a quantitative problem within a prescribed range of values that are deemed to be within acceptable limits for the calculation. This type of question is a single scorable unit.
Example of a fill-in-the-blank question
A PMMA phantom, 20 cm thick, is exposed to an x-ray beam with an effective linear attenuation coefficient of 0.19 cm-1. The fraction of the beam attenuated is _______.
(Enter a fractional number between 0 and 1, with three significant digits.)
Answer: 1 – e-(20*.19) = 0.978. Accepted values are 0.975 to 0.981.
Point-and-click question types require the candidate to identify the region in an image, illustration, or figure that matches the requested information by using the computer mouse to point and click on the area. The last click recorded is the one submitted for evaluation, and when the click is within the predetermined acceptable area, one scorable unit is earned.
Example of a point-and-click question
In the image below, identify the region where slice thickness accuracy can be evaluated. Use the mouse pointer and click with the left mouse button.
Answer: The red oval (image on right) indicates the acceptable area for the candidate to identify to earn 1 scorable unit.

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