212 Lesson 1: Digital detectors & imaging characteristics

Modulation transfer function (MTF)

Measure of imaging system’s contrast and spatial resolution capabilities, MTF of 1.00 is perfect

Bit depth

Maximum range of pixel values a hardware can store

Detector element (del)

Individual hardware cell in DR IR capable of a single electronic readout

Amorphous silicon (a-Si)

Indirect DR process that converts X-rays to light and then electric signal

Voxel

3D cube of tissue sampled by imaging machine to build digital image

Quantum noise/mottle

Grainy/speckled appearance, more apparent at low exposure levels

Signal to noise ratio (SNR)

Percentage of useful signal to destructive noise within acquired image data

Matrix

Collective rows and columns of pixels/dexels that make up area of IR

Nyquist frequency

Minimum required sampling frequency to keep image free of aliasing artifact; = double highest frequency recorded; limits spatial res.

Amorphous selenium (a-Se)

Direct DR process by which X-rays are converted to electronic signal

Indirect conversion DR

DR unit whose IR converts X-rays to light (phosphor layer) and then electric charge

Direct conversion DR

DR unit whose IR converts X-rays directly into electrical charge

CMOS

Complimentary metal oxide semi-conductor; camera device that converts light to electrons

CCD

Charged coupled device; converts light to electrons

Dynamic range

Range of signal intensity/gray levels a software system can detect and display

Detective quantum efficiency (DQE)

Ability of del to absorb Xray/light; its sensitivity to photons

Pixel

2D picture element/cell in image, capable of producing entire range of gray levels for the system

Fill factor

Percentage of del’s area dedicated to photon absorption