Week 10: Fluoro Unit Configurations and Digital Acquisition

Question 1

Image Intensifier (II)

Answer 1

• electronic device which receives the image forming x-ray beam
• purpose is to intensify and convert into visible light image
• newer inits replaced by flat panel detector (FPD)

Question 2

Video Monitoring System (Mobile Viewing Station)

Answer 2

• flat panel monitors
• high resolution
• used for viewing images during the exam
• receives electronic signal and converts into a visible image

Question 3

Fluoro Tube/Generator

Answer 3

• very similar to gen rad tubes
• converts electrical energy into x-rays
• designed to operate for longer exposures with lower mA
• generators are high frequency and higher heat capacity than gen rad

Question 4

Tube Under Table Configuration

Answer 4

• allows operator to be close to patient during exam
• can be controlled using foot switch
• minimum source to skin distance is 38cm
• most common configuration

Question 5

Tube Over Table Configuration

Answer 5

• greater distance between the tube and the patient and II which improves image quality and reducing radiation skin dose to patient
• radiation hazards to operator because of scatter but also from the primary beam
• tech can’t be as close to patient to be of assistance, must step back during exposure

Question 6

C-Arm Configuration

Answer 6

• mobile
• can be positioned under or over the table
• commonly used in OR
• operators must always be vigilant of source to skin distance, minimum of 30cm

Question 7

Housing

Answer 7

• metal construction, lead lines to absorb off-focus radiation
• provides structural support and protection from rough handling
• protects the vacuum

Question 7

Angio Fluoroscopy Units

Answer 7

• large diameter, thick anodes because the x-ray tube must tolerate high heat loads
• high power rating for rapid sequence serial radiography
• c-arms are floor/ceiling mounted, table floats
• small (0.3mm) focal spots must be available for imaging small vessels

Question 8

Glass Envelope

Answer 8

• vacuum tube that allows free flow of electrons from the photocathode to the anode
• can experience as much a 1 coin fro the outside

Question 9

Input Phosphor Screen

Answer 9

• receives x-ray photons and emits light proportional to the absorption of the x-ray photons
• concave surface to improve spatial resolution by maintaining the distance between each point on the input screen and its corresponding location on the output screen
• coated with sodium activated cesium iodine (CsI) phosphor which emits light
• diameter 6 inches - 23 inches

Question 9

Photocathode

Answer 9

• directly connected to the input screen, made of cesium antimony
• receives light and releases electrons by photoemission (directly proportional)
• an extremely thin protective coating is applied between the input screen and the photocathode

Question 10

Electrostatic Lens

Answer 10

• series of charged electrodes inside the glass envelope
• negatively charged to accelerant, converge and focus electrons to the centre off the ring shaped anode
• elections are focused to a point called the focal point (reverses image)

Question 11

Anode

Answer 11

• circular plate with. hole in the middle for electrons to pass though
• accelerates the electrons from the photocathode to the output phosphor/screen
• positively charged and located inside the envelope immediately in front of the output screen
• voltage difference between cathode and anode of 25-35 kV

Question 12

Output Phosphor Screen

Answer 12

• made of thin layer of zinc cadmium sulphide, 1 inch in diameter
• converts electrons into light
• image at this point is much brighter due to smaller size and additional energy through acceleration process
• an opaque filter of aluminum is placed along the inside of the output screen to prevent light from returning to input screen

Question 13

Charged Coupled Device (CCD)

Answer 13

Light sensitive semiconducting device that generates an electrical charge when stimulated by light and stores this charge in a capacitor, Reads out line by line, quantified and plotted on the matrix.

Question 13

CCD Advantages

Answer 13

• more durable
• more sensitive to light (higher DQE)
• requires less radiation
• higher spacial resolution
• fast discharge time = good for high speed imaging like cardiovascular studies

Question 14

Flat Panel Detector

Answer 14

• replacing the II
• utilizes indirect capture detector or direct capture detector (like gen rad)

Question 15

Advantages of FPD

Answer 15

• streamlined assembly (reduced size and weight)
• large FOV
• multiple operational modes
• not effected by distortion
• less radiation is mag mode
• broader TFT dynamic range and low contrast detectability

Question 16

Last Image Hold

Answer 16

• dose reduction technique during acquisition
• eliminates the need for an additional exposure
• last image from the exposure is help on the screen even though there is no active fluoro happening

Question 17

Frame Averaging

Answer 17

• dose reduction technique during acquisition
• combining multiple frames to reduce noise, requires less mA to minimize QM
• objects must be moving slow or lag will be noticeable

Question 18

Pulsed Fluoroscopy

Answer 18

• reduces dose to patients and healthcare providers while maintaining high quality images
• uses higher mA so there will be less QM resulting in better image sharpness
• the dose is pulsed so even though the mA is higher, the radiation is not being emitted constantly which reduces overall exposure

Question 19

Interrogation Time

Answer 19

The time required for the tube to switch on and to get to selected mA and kV

Question 20

Extinction Time

Answer 20

The time required for the x-ray tube to be switched off

Question 21

Duty Cycle

Answer 21

The time the tube is energized. Ex: tube is energized for 100ms every second = 10% duty cycle. Decreased number of pulses per second = lower dose to patient and staff.

Question 22

Digital Subtraction Angiography (DSA)

Answer 22

Removing or subtracting background structures from an image so that only contrast media-filled structures remain.

Question 23

Temporal Mask Subtraction

Answer 23

1. initial mask image of still structures is taken 2. contrast is injected 3. as dynamic contrast flows through the static mask image is able to be subtracted by the computer 4. vessels can be seen unobstructed by bone motion between images (mask image and CM image) = mis registration

Question 23

Dual Energy Subtraction

Answer 23

- based on attenuation difference between tissues and attenuation of contrast medium 1. during the procedure dual kVs are used 2. the difference in PE absorption fro the two kVs can be evaluated 3. the computer can remove bone or soft tissue because it can recognize the k-edge absorption of contrast media

Question 24

Hybrid Subtraction

Answer 24

- combines temporal and energy subtraction - soft tissue subtracted by energy subtractions, bone by temporal

Question 25

Road Mapping

Answer 25

- permits real-time catheter guidance/navigation for endovascuar procedures with a contrast background - superimposes live fluoro over previously subtracted image so previously subtracted image acts like a map to follow - can see black guide wire or catheter and white vessel

Question 26

Remasking (DSA Only)

Answer 26

Selecting another ask image in order to obtain the best subtracted image of the anatomy of interest. This is helpful in removing any motion that may be present after the initial mask.

Question 27

Pixel Shifting (DSA Only)

Answer 27

Used when the patient moves slightly from the mask image to the injection image. It allows the user to move the mask image to correspond to the patient movement. Corrects misregistration artifacts.

Question 28

View Tracing

Answer 28

Combines the numerous frames into one image to demonstrate a completely filled contrast structure.