*****Medical / Digital Image Descriptors (Test 2)

Radiographic Quality

What refers to the faithfulness and exactness with which the structure is imaged on a radiograph?

Spatial resolution, contrast resolution, noise, artifacts

What affects radiographic quality?

Resolution

What is the ability to image two separate objects and visually detect one from another?

Spatial Resolution

What refers to the ability to image small objects that have high subject contrast, like breast calcifications or the sharpness of detail?

Focal spot size/filament length, SID, SOD, OID, pixel size, matrix size, motion

What all affects spatial resolution?

Pixel Size

In digital imaging, what is spatial resolution limited by?

Decrease pixel size

To increase spatial resolution, what needs to happen to the pixel size?

Decrease focal spot size and decrease filament length

To increase spatial resolution, what happens to the focal spot size and filament length?

Contrast Resolution

What refers to the ability to distinguish anatomic structures of similar subject contrast, like the liver and spleen?

high / low

Contrast resolution incldues _________ contrast and ________ contrast

Visibility of detail

What refers to the ability to visualize recorded details on an image?

IR exposure and contrast resolution

To have a good visibility of detail on an image, what two things need to be optimized in the middle?

Radiographic Noise

What refers to the fluctuation of the IR exposure of an image or the fluctuation of x-ray interactions with the IR?

Anything undesirable on a radiograph

What is another definition of radiographic noise?

Electronic noise, quantum mottle, scatter radiation, and artifacts

What are the different types of noise?

Electronic Noise

What type of noise is inherent in the image receptor?

Quantum Mottle

What type of noise is caused by insufficient mAs and is controlled by the technologist?

Quantum Mottle

Which type of noise is the main contributor to noise on a radiograph?

mAs decreased resulting in quantum mottle; mAs was increased and kVp was decreased

With faster speed systems, as the speed increased, what happened to mAs, and what did it result in? What was done to prevent this result?

12 inches

How many inches are in 1 foot?

3 feet

How many feet are in 1 yard?

- 6 feet

- 2 yards

- At how many feet is a chest X-ray performed?

- At how many yards is a chest X-ray performed?

2.5 cm

Approximately, how many centimeters are in 1 inch?

- 180 cm

- 100 cm

- 90 cm

- How many centimeters are in 72 inches?

- How many centimeters are in 40 inches?

- How many centimeters are in 36 inches?

Size distortion

What type of distortion occurs when the image is larger than the object?

Increase SID or Long SID

For minimum magnification, what needs to happen to the SID?

Increase SOD or Long SOD

For minimum magnification, what needs to happen to the SOD?

Decrease OID or Short OID

For minimum magnification, what needs to happen to the OID?

MF = SID / SOD

What is the magnification formula?

SID - OID = SOD

What formula is used to find the SOD?

Image size / MF = Object Size

What formula is used to get the object size in an image?

Object size x MF = Image size

What formula is used to get the image size?

14.5 cm (object size)

If the SID is 44 inches, the OID is 4 inches, and the image size is 16 cm, what is the true size of the object?

16 cm (image size)

If the SID is 44 inches, the OID is 4 inches, and the object size is 14.5 cm, what is the size of the image?

Shape Distortion

What type of distortion refers to the unequal magnification of an object or the image not being the same shape as the object?

Elongation

What type of shape distortion is where the image is longer than the object?

Foreshortening

What type of shape distortion is where the image is shorter than the object?

If the divergent ray is parallel to the body part

What causes foreshortening?

If the divergent beam is perpendicular to the body part

What causes elongation?

- Parts that lie away from CR

- Improper tube/part/IR alignment

- Angulation

- Part shape

- Part thickness

What 5 things can increase distortion?

Thick body parts

Between thick and thin body parts, which is more distorted?

Spherical/cuboidal body parts

Between spherical/cuboidal parts and flat/tubular parts, which is more distorted?

Distortion increases

If an object is lying at an angle in the body, what happens to the distortion?

- Star will be towards the feet

- Triangle will be in thr middle

- Square will be towards the head

On an AP Axial Townes view, how will the objects be positioned on the IR?

Focal-Spot Blur

What refers to the un-sharpness due to the effective focal spot not being a precise point?

Increase SID or Long SID

To increase spatial resolution, what needs to happen to the SID?

Decrease OID or Short OID

To increase spatial resolution, what needs to happen to the OID?

Anode side of tube

What side of the X-ray tube gives you increased spatial resolution?

image / subject

__________ contrast x ___________ contrast = radiographic contrast

Post-processing and bit depth

In digital imaging, what is image receptor contrast a factor of?

Subject Contrast

What refers to the differential absorption of the radiation within adjacent body parts?

- Patient thickness

- Tissue physical density

- Atomic number

- Shape of object

What factors affect subject contrast?

- Fast or short exposure time

- Communicating with the patient (hold breathe/don't move)

- Restrain patient

How is motion reduced?

- Increased or long SID

- Decreased OID or short OID

How is the focal spot blur reduced?

- Short or decreased OID

- Body part parallel to IR

- CR on center of body part

- Immobilize patient

What are the 4 ways that proper positioning can improve radiographic quality?

- Shortest exposure time possible

- Use three phase/high frequency generator

- Optimum mA and kVp for optimum IR exposure and contrast

What are the 3 ways that technique factors can improve radiographic quality?

Intensity and x-ray beam energy increase

As kvp increases, what happens to both the intensity and x-ray beam energy?

More radiation penetrates all the way through the patient to reach the IR

As kVp increases, what happens to the penetration of radiation?

Subject contrast decreases

As kVp increases and there is more penetration, what happens to subject contrast due to less differential absorption?

Compton scatter increases

As the KVP increases, what happens to Compton scatter?

Image contrast decreases

As the kVp increases and more Compton scatter occurs, what happens to image contrast?

No

Are the effects of digital imaging more noticeable with increased kVp?

Patient absorbed dose decreases

As the kvp increases, what happens to the patient's absorbed dose?

Patient ESE stays the same

If kVp is increased and mAs is decreased to compensate, what happens to the patient's entrance skin exposure?