Ch. 16 Bushong Challange Questions - Digital Radiolgraphy

Charge-coupled device

A charge-coupled device is solid state system that converts light into an electrical signal with very high spatial resolution.

Spatial Resolution

Ability to render very small, high-density objects visible on the image.

Amorphous

Amorphous = lacking form. Not crystalline in form, but like a paint of crystals.

Describe the role of an AMA-TFT assembly.

An active matrix array thin-film transistor (AMA-TFT) assembly is an image receptor for digital radography.

Fan x-ray beam

An x-ray beam collimated to appear as a cooling fan. Used in CT and SPR.

What are the capture, couple, and collection stages for a-Se-based DR?

Capture=selenium, coupling=selenium, collection = thin film transistor

What are the two principal phosphors used in DR?

Cesium Iodine (CSI) and Gadolinium Oxysulfide (GdOS).

What are the respective atomic numbers for the x-ray capture elements of the various DR systems?

Cesium-55, iodine-53, gadolinium-64, oxygen-8, sulfur-16, selenium-34.

By what four methods can a digital radiograph be produced?

Charge-coupled device, Cesium Iodide married to Amorphous Silicon, Gadolinium Oxysulfide married to Amorphous Silicon, and Amorphous Selenium.

How does DMT show promise for improved breast cancer detection?

DMT shows promis for improved breast cancer detection with superior contrast resolution.

DMIST

Digital Mammography Imaging Study Trial; an ACRIN (American College of Radiology Imaging Network) trial to see if digital mammography is equal to screen-film mammography.

Describe some applications for use of a CCD in addition to medical imaging.

Digital cameras and astrological observations

What properties make GdOS a good DR image receptor?

GdOS has higher detective quantum efficiency (DQE).

Why is fill factor important?

In DR, the smaller the pixel size, the less the fill factor. Lower fill factor requires increased patient dose, so it's a tradeoff.

Two conductiong leads are present for each digital pixel. What are they, and what do they do?

One lead is the address driver; it identifies individual pixels and causes them to release their electric charge. The other lead is the data line which conducts the signal to the data acquisition system (DAS).

What is the principal advantage of SPR over tiled CCDs for use in DR?

SPR does not require that static images be fitted together.

SPR

Scanned Projection Radiography (SPR) The use of a fan x-ray beam and linear detector array to form a projection radiograph.

Scintillation phosphor

Scintillation phosphor, such as NaI, CsI, and other similarly behaving crystals that emit light in response to an x-ray interaction.

What is the meaning of "sensitivity" in DR?

Sensitivity in DR is how low an x-ray intensity can be detected for imaging.

Spatial Frequency

Specification of object size in inverse size. Measured in line pair per millimeter.

What was the result of the DMIST investigation?

That digital mammography is equal to screen-film mammography in all patients except younger patients or those with dense breasts; there, digital mammography is superior.

How does pixel size in CCD DR compare with that in other forms of DR?

The CCD has smaller pixels.

Tomosynthesis

The acquisition of several projection radiographs from different angles in digital form that are then reconstructed into layered images.

What are the consequences of producing flat panel digital image receptors with smaller pixels?

The consequences of producing flat panel digital image receptors with small pixels are noisy images.

Dynamic Range

The number of gray levels that can be rendered on the image. Sometimes termed "bit scale" for the number of bits available in the image. (example, 12bits contain 4096 shades of gray.)

How is the tiled CCD mosaic made to appear as a single image?

The tiled CCD mosaic is made to appear as a single seamless image at the edge of each CCD by interpolation of pixel values at each tile interface.

How does the image line spread function change for the four types of DR?

This is still very much under investigation. The use of amorphous selenium should provide best spatial resolution, but the problems with digital element size and fill factor restrict this.

Why is interest in digital mammography tomosynthesis on going?

Tomosynthesis is a tomography imaging system which results in increased contrast resolution, as do all tomography systems.

What is meant by "limited spatial resolution?"

most vendors identify the spatial frequency associated with the 0.1 MTF as the limiting spatial resolution expressed in lp/mm.