Exam 3: DR Technology, Quality Control, PACS, & Fluoro

What material is used in direct conversion? What are the steps?

Involves a PHOTO-CONDUCTOR called amorphous selenium!!

Steps: Takes x-rays and converts them over to an electrical signal which is then stored in a DEL.

Which conversion has TFT arrays?

BOTH!!!

What item(s) control the line read out?

Address/line driver (circuit): controls the circuits (opens & closes the switches) and the line by line readout!! Puts a small potential difference to get electrons to flow whenever the switch is DOWN (so current can flow!)

What material is used in indirect conversion? What are the steps?

Involves a SCINTILLATOR, either cesium iodine or Gadolinium Oxysulphide.

Photo-detector is amorphous silicone.

Steps: X-rays come in and are converted to visible light by the scintillator and then is converted over to the electrical signal by the photo-detector amorphous silicone

What are the differences in the two scintillator's?

Gadolinium Oxysulphide: older & unstructured, powder looking items. The x-ray will come in and the phosphor will be spread over a larger area which will have a loss in detail, spatial resolution!

Cesium Iodide: newer & structured, has a crystal structure. Less light spread on this one so it creates better spatial resolution (detail)

What does a field-effect transistor (also known as TFT) do?

Controls the opening and closing of the switches. If switch is open, electrical signal cannot leave!

What is gain calibration?

"flat-fielding"; this is a process for removal of unwanted densities that interfere with diagnostic image information, corrects the flaws in the detector

What is a dead pixel?

A pixel that does not display any color due to the fact it is broken and the TFT array is not working

How are the flat panel array designs read out? Is it line by line? What about control line voltage?

They are read out line by line! One side is the integrated circuits or address driver that controls the line read out (aka. opens/closes the switches). The other side of the TFT array collects the signal and amplifies it!!

Does the read out for the flat panel array allow for it to be returned to it's original state and used again for another x-ray?

Yes!! It resets so it can be used again!

What is quality control?

Deals with instrument and equipment

Ex: equipment checks

What is quality assurance?

Deals with people

Ex: number of repeat

What is HVL? What does it measure?

half-value layer

The thickness of absorbing material needed to reduce the x-ray intensity (quantity) to half its original value. AKA: quality of the beam AKA penetrating ability

What is exposure linearity?

Consistency in output intensity at selected kVp settings when settings are changed from one mA + sec combination to another, have to have a consistent radiation adjacent.

--> Must be within 10% for adjacent mA stations!!

What is exposure reproducibility?

consistency in output in radiation intensity for identical generator settings from one individual exposure to subsequent exposures. AKA: total amount of radiation coming out of the x-ray tube. kVp and mAs together!!

--> Must be within + or - 5%

What is minimum amount of filtration in the x-ray tube?

2.5 mm of aluminum

What is the distance indicator?

SID must be what you set it at! If it is set at 40 in, it needs to be at 40 in.

--> + or - 2%

What are the steps of the image intensifier?

1. Input phosphor (Cesium Iodide) takes x-rays and converts them into visible light

2. Photo-cathode converts the visible light into electrons

3. Electrostatic focusing lenses accelerates the electrons across the image intensifier to hit the

4. Output phosphor (zinc cadmium) which will the convert the electrons back to visible light

What is brightness gain?

Overall ability to brighten up the image (Flux gain & minification gain together)

What is flux gain?

The acceleration of electrons between the input and output phosphor.

What is the minification gain?

Concentration the electrons into a small one inch area.

Ex: big input phosphor --> small output phosphor

What is the brightness gain formula?

Flux gain x minification gain

What is the flux gain formula?

output/input

What is the minification gain formula?

input ^ 2/output ^ 2

What is automatic brightness control?

Automatically changes the kVp and mA to maintain image brightness

How does mag mode (magnification) affect patient dose and the visibility of small objects?

Increased patient dose, increased visibility

Where is the x-ray tube and image intensifier located on the fluoro system?

Tube: under the table

Intensifier: above the patient

What is the SSD for fixed and mobile fluoro units?

Fixed: 15 in

Mobile: 12 in

What is the maximum exposure rate at table top?

100 mGy/min

What is the total amount of filtration needed in a fluoro unit?

2.5 mm of aluminum

What is the required thickness of lead required in a bucky slot cover and protective curtain? Lead aprons and thyroid covers?

Bucky & curtain:.25 mm

Apron & thyroid: .5 mm