Fluoro: Image Recording Systems

Each spot film may be equal to more than ____ minute(s) of fluoroscopic time.

1

When viewing cine film as a movie (if projector shows each frame once), framing at _____ frames/sec will show flicker.

30

Difference between 16mm & 35mm format in cinefluorography

35mm requires an increased dose compared to 16 mm 35 mm will also produce a higher quality image

Eyes can perceive flicker up to ____ frames/sec

50

Framing frequency (rates) are derivatives of _____ Hz.

60

When viewing cine film as a movie (if projector shows each frame once), framing at _____ frames/sec will be perceived as continuous motion without flicker.

60

What is a CCD?

A semiconducting device capable of storing a charge from light photons striking a photosensitive surface.

How is synchronization driven?

By synchronous motors controlled by the frequency of line voltage (60 Hz).

How are video disc frame frequency rates determined?

By the physiological motion of organ being imaged.

What causes the single highest dose rate of all fluoro recording mediums?

Cassette spot filming

How cinefluorography works

Cine cameras operate by recording a series of static images at high speed. When images are projected at the same high speed, the eye becomes incapable of differentiating the separate images and perceives them as a single image in motion (i.e. a movie)

Total Over Framing

Diameter of circular image from optical system is equal to diagonal measurement of rectangular aperture (30 mm) All of the film is used but 39% of the image is wasted

Over Framing

Diameter of circular image from optical system is larger than shortest dimension of film Part of the image is lost

Exact Framing

Diameter of intensifier image at the output phosphor and the smallest dimension of the frame (18mm) are the same. No part of the image is lost but only 58% of the film is used

What is the f-number of an optical system dependent on?

Diameter of the lens & optical focal length (distance between the lens & image plane or film surface)

Relationship between framing frequency & patient dose. Why?

Directly Proportional Due to dose accumulation.

Relationship between the diameter of the lens and the amount of light being transmitted through.

Directly Proportional Larger Diameter = More Light

Relationship between f-number & patient exposure.

Directly Proportional Lower f-number = Less Exposure Required

Relationship between focal spot length & magnification.

Directly Proportional Shorter (less) Focal Length = Less Magnification

Advantage of cinefluorography

Dramatically increased resolution

2 methods of recording the fluoroscopic image

Dynamic & Static

How does the CCD linear response curve effect patient dose & contrast?

Enables imaging with low light levels (less dose) possible with retained contrast resolution.

How does photospot work?

Film in a roll is positioned in the aperture prior to exposure. Once the shutter opens & the film is exposed & the shutters close again. The film changer advances the roll into a receiver magazine for transport & wet processing.

How does the grid being powered on or off effect electron flow and radiation through the tube? & why?

Grid on = no electron flow to anode = no radiation even though tube is held at peak Kilovoltage. Because it is a negatively charged grid (screen) across the cathode focusing cup

Photospot is a ___________ dose than simple fluoroscopy, & a ___________ dose than cassette spot filming.

Higher Lower

Increased motion requires __________ framing frequency.

Increased

Relationship between focal spot length & light concentration at the image plane.

Indirectly Proportional Shorter (less) Focal Length = Increased light concentration at the image plane (film surface)

Relationship between f-number & light.

Indirectly Proportional The lower the f-number = more light

Relationship between f-number & lens speed.

Indirectly proportional; The lower the f-number = faster lens

How does the CCD work?

Light strikes the crystalline silicone Electrons are released proportionally to the intensity of the incident light The video signal is emitted in a raster scanning pattern where they are discharged in to a conductor CCD can then be sampled pixel by pixel (in a raster format)

CCD has a ________ response curve as compared to other image receptors which have __________ shaped curves

Linear Sigmoid

Iris (or diaphragm) Location & Function

Located between the camera lens and shutter. Restricts the divergence of light from the lens. Controls amount of light reaching the film.

Under Framing

Maximum size of Fluoro image is smaller than smallest dimension of the frame. Should be avoided.

Where do the photospot film cameras photograph the image?

On the output phosphor of the image intensifier.

Where is the CCD located?

Output phosphor of the image intensifier.

Disadvantage of cinefluorography

Patient exposure is significantly greater

How is spatial resolution of a CCD determined?

Physical size & pixel count

What does the grid biased tube control?

Radiation pulse rate

Static image recording includes...

Radiographic Cassette Photospot Camera Charged-Coupled Device

How does video tape recording work?

Recording and playback heads magnetically arrange and read a pattern of ferrous particles on the surface of a tape, which produces a video signal.

Video disc recorders are used to record...

Single field Single frame Short sequence

How is photospot different from cine?

Slower Use larger film sizes (better quality, more dose)

Advantage of video recording

Storing images for later review, photographing and printing as a permanent record.

Interrogation Time

The length of time required for the generator to come on and achieve the necessary kVp and mAs levels.

Extinction Time

The length of time required to shut the generator down in preparation for the next pulse.

Cine-Synchronization

The operation of the camera shutters at the same frequency as x-ray pulses. Exposure only made when film is not moving.

Electronic Radiography

The term used when a video disc recorder is interfaced with the fluoroscope.

Define Framing

The use of the available film area used for image capture.

True or False: Cine film can be viewed as both a movie or in stop- action.

True

Dynamic image recording includes...

Video Tape Recording Cinefluorography Digital Video

How does digital image capture work?

Video signal must be converted from analog to digital (ADC). Data is then stored & can be manipulated. When reviewing the image, it must be converted back to analog by the DAC.

When are stat images necessary?

When a permanent record of the fluoroscopic examination is required.

Advantages of video tape recording

• Available for instant replay w/o any intermediate processing • Patient exposure is not increased • Can be viewed in slow motion or stop frame

Disadvantages of video tape recording

• Lower resolution than cinefluorography • Fixed framing rate at 30 frames/sec