Chapters 1,2,4,5 - Carter book

Latent image

Captured the image but it has not be developed or digitized.

-Always sent to PACS

-formed by CR or PSP systems, when xrays interact with the PSP, they are captured and released in the reader

PSP

Photostimulable phosphor Plate

1. In CR you have a cassette → inside it is the PSP plate

2. Xrays hit the phosphor on the plate and store the image as trapped electrons

3. Then the plate goes into the CR reader, laser scans it, releases stored energy as blue light

4. Light gets turned into digital image

-Phospher is stimulated by light (ony in CR systems): uses storage phosphor plates to produce projection images

-Always sent to PACS

IP layers and purpose

IP - Imaging plate

1. Protective → protects phospher

2. Phosphor/active → PSP barium fluorohalide

3. Reflective → Sends light forward

4. Conductive→Absorbs/reduces static electricity

5. Color/light shielding→ Absorbs stimulating light

6. Support→Protects back of cassette

7. Backing→Protects back of cassette

8. Barcode→ Match image with patient

LABEL

1. Protective layer

2. Light reflective layer

3. Support layer

4. Backing layer

5. Phosphor layer

6. Conductive layer

7. Light shielding layer

Squence CR

1. IR placed in reader

2. Laser scans PSP, releasing the xrays captures by light

3. Photomultiplier amplies the light

4. Light is converted to digital signl via ADC

5. IP is erased by flooding it with light

ADC

Analog (light or electric) to digital converted (numbers)

TRANSLATOR

Photoconductors

Absorb xrays and convert to an electrical charge

-Direct system

Scintillators

Phosphors that produce light when absorbing xrays

-Indirect system

Direct Capture

Immediately converted into an electrical signal

-Photoconductor or radition conversion material = Amorphous selenium (aSE)

-Xrays converted to electrons and stored in TFT detectors

-TFT photosensitive array made up of DEL (detector elements or pixels), each pixel(DEL) contains a photodiode that absorbs electrons + generates an electric charge

-The FET (field effect transitor) sends the charge to image processor

Indirect capture

Two step process

-Uses a scintillator Gd202S or CSI that converts xrays to light

-Sent to a (Photodetector) photosensitive array made up of small pixels (Amphous silicon) to convert light to electrons

-TFT photosensitive array made up of DEL (detector elements or pixels), the DEL absorbs electrons + generates an electric charge

-The FET (field effect transitor) sends the charge to image processor

BLUE= same as direct capture

Gd202S (Turbid)

-Unstructed

-Allows light to escape

-Very rugged so good for portables

-Scintillator

CSI

-More popular

-Structured, thin needles

-Greater detection

-Once very delicate but improvements have been made

-Scintillator

Analog capture

Exposure latitude is based on characteristic response of film which is NONLINEAR

Digital capture on a graph?

Linear capture (straight line)

DQE

Detective Quantity Effeciency - MAs

• How efficiently a system converts the X-ray input signal into a useful output image

• DQE is a measurement of the percentage of X-rays that is absorbed when they hit the detector.

• The takeaway - is the phosphors used in any system (film/PSP systems/Cassettless DR systems) and the way they interact and release x-ray energy impacts DQE

Direct - Highest

Indirect

CR - Lowest

Pixel

the smallest element in a digital image

Pixel bit depth

-the number of bits within a pixel

-Each pixel contains pieces of information

Matrix

square arrangement of numbers in columns or rows, numbers correspond to discrete pixel values

Field of view (FOV)

the amount of body part included on the image

-Larger FOV = more area is imaged

-Change FOV = no change is matrix size

Relationship = Spatial resolution and pixel size

Increase spatial resolution = Decreased pixel size

Relationship = matrix and pixel size

increased matrix size= decreased pixel = increase spatial resolution

Relationship = matrix and number of pixels

increased matrix size = increase number of pixels

Relationship = matrix and spatial resolution

Increase matrix size = Increased spatial resolution

Kstd - air kerma or gray

Standard radiation exposure

measurement of the beam afer it is filtered

K_ind radiation

What strikes the IR or the detector

-Measurement of the radiation that was the incident exposure on the IR for the exposure

KTGT 

Target exposure Index

target values established by the equipment system vendor- what is supposed to hit the detector

Deviation Index

kind/KTGT

To determine if an image is overexposed or underexposed

want it to be 0

Spatial resolution is affected by what?

SID

OID

Tube angle

Focal spot size

DICOM

Digital imaging and communications in medicine : PACS can accept any image that is DICOM

Standard to make sure: images can open at any hospital, patient info stays attached, PACS systems know how to store images, and different machines all communicate the same way - Using the same format for all

CR - Konica system

Indirect system

Range 100-300