Digital Radiography and PACS Flashcards

In computed radiography (CR), the image is captured by a photostimulable phosphor (PSP) plate. To read the image, the PSP plate is exposed to:

Answer: A laser beam that stimulates the stored energy to emit visible light

In CR, the PSP plate stores x-ray energy as trapped electrons; a laser beam stimulates these electrons, causing photostimulated luminescence (PSL) that is detected and converted to a digital image.

Direct digital radiography (DR) flat panel detectors using amorphous selenium (a-Se) are classified as:

Answer: Direct conversion detectors (x-rays directly produce electrical charge)

Amorphous selenium flat panel detectors are direct conversion detectors — x-rays directly ionize the selenium layer, producing electron-hole pairs that are collected as an electrical signal without intermediate light production.

In digital radiography, the exposure index (EI) number primarily reflects:

Answer: The amount of radiation exposure received by the image detector

The exposure index (EI) is a standardized number that indicates the exposure reaching the image receptor — it reflects the radiation dose to the detector, not the technique factors.

PACS (Picture Archiving and Communication System) uses which standard protocol for storing, transmitting, and displaying medical images?

Answer: DICOM (Digital Imaging and Communications in Medicine)

DICOM is the universal standard for medical imaging data, defining how images are stored, formatted, transmitted, and displayed — it is the foundation of PACS interoperability.

The primary advantage of using indirect conversion flat panel detectors with cesium iodide (CsI:Tl) over gadolinium oxysulfide (GOS) screens is:

Answer: CsI:Tl has a needle-like crystal structure that channels light to the detector, reducing light spreading and improving spatial resolution

CsI:Tl's columnar needle-like crystal structure acts as a light guide, channeling emitted light perpendicular to the detector surface, which minimizes lateral light spreading and preserves spatial resolution.

Detective quantum efficiency (DQE) in digital radiography describes:

Answer: How efficiently the detector converts x-ray exposure into a useful signal relative to ideal detector performance

DQE is the ratio of output SNR² to input SNR² across spatial frequencies, measuring the efficiency with which the detector uses the incident x-ray photons to produce a noise-limited image.