Computed Tomography Test Computed Tomography Science 5

Question 1

Which type of CT detector converts X-ray photons directly into electrical charge using amorphous selenium?

Accepted Answer

Direct-conversion flat-panel detector

Answer

Direct-conversion detectors (e.g., amorphous selenium) convert X-rays directly to electrical charge without an intermediate light step, potentially improving spatial resolution.

Question 2

Spectral CT using photon-counting detectors differs from energy-integrating detectors mainly because it:

Accepted Answer

Counts individual photons and records their energy levels

Answer

Photon-counting detectors register each photon individually and bin them by energy, enabling true spectral decomposition without energy overlap between bins.

Question 3

In CT, the concept of 'noise power spectrum' (NPS) provides information about:

Accepted Answer

The frequency-dependent distribution of image noise

Answer

The NPS (or Wiener spectrum) describes how noise energy is distributed across spatial frequencies, capturing the texture and magnitude of noise in CT images.

Question 4

Which reconstruction algorithm uses a statistical model of the imaging process to minimize a cost function iteratively, achieving better noise properties than FBP?

Accepted Answer

Maximum-likelihood expectation maximization (MLEM)

Answer

MLEM iteratively updates the image estimate to maximize the likelihood that the projection data would be observed given the current image, reducing noise and artifacts.

Question 5

In helical CT, the 'pitch factor' is defined as table advancement per rotation divided by:

Accepted Answer

Total detector width (beam collimation)

Answer

Pitch = table feed per 360° rotation / total beam collimation width; a pitch of 1 means table advance equals the beam width with no overlap or gap.

Computed Tomography Test Practice Test

Computed Tomography Test Practice Test

Computed Tomography Test Computed Tomography Science 5