Practice Test Geeks(ARRT) American Registry of Radiologic Technologists Computed Tomography Certification Practice Test
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7 cards from real ARRT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which statement BEST describes the relationship between CT noise and mAs?

    Answer: Noise is proportional to 1/√mAs

    CT noise follows Poisson statistics; doubling mAs quadruples photons but only reduces noise by a factor of √2, making noise proportional to 1/√mAs.

  2. Cupping artifact on a CT image of a large cylindrical phantom most likely indicates:

    Answer: Beam hardening due to preferential absorption of lower-energy photons

    Cupping artifact occurs because low-energy photons are preferentially absorbed by the periphery, hardening the beam and making the center appear falsely darker.

  3. In CT, contrast-to-noise ratio (CNR) is BEST described as:

    Answer: The difference in HU between two structures divided by image noise

    CNR = (HU_structure − HU_background) ÷ noise standard deviation, quantifying how well a structure stands out against background noise.

  4. Which reconstruction kernel (filter) choice produces the HIGHEST spatial resolution but MOST noise in CT?

    Answer: Sharp/edge-enhancing kernel

    Sharp or bone kernels enhance high-frequency data to improve edge detail but amplify noise, making them high-resolution but noisy.

  5. Automatic tube current modulation (ATCM) in CT primarily aims to:

    Answer: Maintain consistent image noise while minimizing patient dose

    ATCM adjusts mA based on patient attenuation in real time, delivering higher current through thicker/denser regions to maintain uniform noise and reducing dose elsewhere.

  6. The spatial frequency at which the MTF falls to 10% is commonly used to define:

    Answer: The limiting spatial resolution of the CT system

    MTF10% represents the highest spatial frequency the system can transfer with 10% modulation, effectively defining the limiting resolution.

  7. When performing a CT colonography, the technologist selects a 0.625 mm detector row width versus 5 mm. This change PRIMARILY improves:

    Answer: Longitudinal (z-axis) spatial resolution enabling multiplanar reformats

    Thinner detector rows provide finer z-axis sampling, enabling isotropic voxels and high-quality multiplanar reformats for polyp detection.