Ch. 17 Carlton

What is Attenuation?

The reduction in X-ray photons remaining in the beam after passing through a thickness of material.

What does Increased part thickness do?

Results in increased attenuation.

What is Attenuation a result of?

Photoelectric absorption and Compton scattering

What does Photoelectric absorption provide?

radiologically significant information.

What does Compton scattering provide?

No useful information, contributes to personnel exposure.

Why is the Human Body considered an Attenuator?

The patient is the radiographer's greatest variable because the composition of the human body determines its radiographic appearance.

What are the four major substances accounting for variable attenuation?

Air, Fat, Muscle, Bone

What is the Effective atomic number of Air?

7.78, greater than fat or muscle.

What is the tissue density of Air?

Low tissue density.

What is the photon absorption of Air?

Absorbs few photons.

How does Air affect the Image Receptor?

Results in increased area of exposure on the image receptor.

What type of tissue is Fat?

Soft tissue.

What is the Effective atomic number and tissue density of Fat?

Similar to water & slightly less than muscle.

What is the Tissue density of Fat compared to muscle?

Less than muscle.

What type of tissue is Muscle?

Soft tissue.

What is the Effective atomic number and tissue density of Muscle compared to fat?

Slightly higher atomic number and tissue density than fat.

What element is abundant in Bone?

Calcium is the highest atomic number of elements found in the body.

What is the Tissue density of Bone?

Greatest tissue density.

How does Bone affect photon absorption?

Absorbs many photons.

How does Bone affect the Image Receptor?

Decreased area of exposure on the image receptor.

What determines a Patient's Relationship to Image Quality?

Overall blackness (density) and differences between the blackness to greys (contrast).

How does Subject Density affect Image Receptor?

Image receptor exposure will be altered by changes in the amount or type of tissue being irradiated.

What is Subject Contrast?

Degree of differential absorption resulting from differing absorption characteristics of tissues in the body.

What is Subject Detail dependent on?

Position within the body and the body's placement in relation to the image receptor.

What is Subject Distortion?

Unless the patient is positioned specifically to demonstrate a particular structure, it may not be accurately represented on the image receptor.

Why are 'Patients radiographers greatest variables'?

Pathology and Radiation Absorption

What is Beam attenuation dependent on?

Thickness and composition of patient's tissues.

How does Pathology affect tissue density?

Can alter the thickness and composition of patient's tissue density.

How does Small, localized pathology affect technical factors?

Does not require a change in technical factors.

What is increased during Additive Conditions?

Increase tissue thickness, effective atomic number, and/or tissue density.

How do Additive Conditions affect attenuation?

Increase attenuation and are inversely related to image receptor exposure.

How do Additive Conditions affect technical factors?

Require an increase in technical factors to properly expose the image receptor.

How does a Thicker, denser part affect penetration?

Requires more penetration (higher kvp)

What is the General technique for Additive Conditions?

Increase in kVp.

What are some Multiple systems examples of Additive Conditions?

Abscess, edema, tumors

What are some Chest examples of Additive Conditions?

Atelectasis, bronchiectasis, cardiomegaly, congestive heart failure (CHF), empyema, pleural effusions, hemothorax and hydrothorax, pneumoconiosis, pneumonia (pneumonitis), pneumonectomy, pulmonary edema, tuberculosis

What are some Abdomen examples of Additive Conditions?

Aortic aneurysm, ascites, cirrhosis, calcified stones

What are some Extremities and skull examples of Additive Conditions?

Acromegaly, chronic osteomyelitis, hydrocephalus, osteoblastic metastases, osteochondroma, Paget's disease, sclerosis

What is decreased during Destructive Conditions?

Tissue thickness, effective atomic number, and/or tissue density.

How do Destructive Conditions affect attenuation?

Decrease attenuation and are directly related to image receptor exposure.

How do Destructive Conditions affect technical factors?

Require a decrease in technical factors to properly expose the image receptor.

What is the General technique for Destructive Conditions?

Decrease mAs.

What are some Multiple systems examples of Destructive Conditions?

Anorexia nervosa, atrophy, emaciation

What are some Chest examples of Destructive Conditions?

Emphysema, pneumothorax

What are some Abdomen examples of Destructive Conditions?

Aerophagia, bowel obstruction

What are some Extremities and skull examples of Destructive Conditions?

Active osteomyelitis, aseptic necrosis, carcinoma, degenerative arthritis, fibrosarcoma, gout, hyperparathyroidism, multiple myeloma, osteolytic metastases, osteomalacia, osteoporosis