Chapter 17 Notes Flashcards
attenuation
reduction in the total number of x-ray photons remaining in the beam after passing through a given thickness of material
attenuation is the result of
x-rays interacting with matter and being absorbed or scattered
amount of attenuation is determined by
amount and type of irradiated material
four major substances account for most of the variations in x-ray absorption
air, fat, muscle, and bone
if a disease causes the affected body tissue to increase in thickness, effective atomic number, and/or tissue density
disease will result in a greater attenuation of the x-ray beam (additive conditions)
if a disease causes the affected body tissue to decrease in thickness, effective atomic number, and/or tissue density
disease will result in less attenuation of the x-ray beam (destructive conditions)
additive conditions require
increasing technique
destructive conditions require
decreasing technique
photoelectric absorption does what to the image
provides radiologic significant information
Compton scattering does what to the image
provides no useful information and contributes to personnel exposure
attenuation is what type of process
exponential
human body is essentially composed of _____ Z# elements
low
on images, what is considered a fifth radiographic density
metal
Z# of air
7.78
characteristics of air
low tissue density; absorbs few photons
characteristics of fat
soft tissue; tissue density similar to water
characteristics of muscle
soft tissue; slightly higher Z# than fat; considered essentially a water density
characteristics of bone
composed of calcium and phosphorous salts; greatest tissue density; high absorption of photons; radiopaque
subject contrast
degree of differential absorption resulting from differing absorption characteristics of tissues
subject density
IR exposure will be altered by changes in amount or types of tissue being irradiated
subject contrast is dependent on
tissue composition as a body part
examples of low subject contrast body part
breast and abdomen
examples of high subject contrast body part
skull, spine, and knee
subject detail is dependent upon
anatomical location within body; body’s placement in relationship to IR; increased distance of anatomical structures from receptor yields less detail of anatomy
subject distortion
misrepresentation of the size and shape of anatomy due to its orientation to path of x-ray beam
size distortion
magnification
shape distortion
foreshortening/elongation
additive conditions
increase attenuation
how are additive conditions related to IR exposure
inversely
what change in technical factors will generally be adequate for most additive conditions
5-15 increase in kVp
destructive conditions
decrease beam attenuation
how are destructive conditions related to IR exposure
directly
what change in technique must occur with destructive conditions
decrease mAs
denisty
quantity of matter per unit of volume measured in kilograms per cubic meter
Z# of fat
6.46
Z# of water
7.51
Z# of muscle
7.64
Z# of bone
12.31
at the atomic level, the body consists primarily of
hydrogen, nitrogen, calcium, carbon, and oxygen
Z# of calcium
20
air is naturally present in
lungs, sinuses, and gastrointestinal tract (small amounts)
little difference in image
low subject contrast
greater difference in image
high subject contrast
larger patients result in
greater distance and less sharpness
thinner patients result in
closer distance and greater sharpness
magnification occurs because
various anatomical structures sit and varying levels
fluid will absorb more radiation than
air
AEC system that adjust for pathological changes automatically results in
increased mAs rather than increased kVp
additive conditions affecting multiple systems
abscess, edema, and tumor
abscess
an encapsulated infection increases tissue thickness and may alter composition, particularly in lungs
edema
swelling causes an increase in tissue thickness and may alter composition, if it occurs in the lungs
tumor
an abnormal new growth in tissue results in an increase in tissue thickness and may alter composition, particularly in the lungs or bones, or when calcification results
additive conditions of the chest
atelectasis, bronchiectasis, cardiomegaly, congestive heart failure, empyema, pleural effusions, pneumoconiosis, pneumonectomy, pneumonia, pulmonary edema, and tuberculosis
atelectasis
a collapse of the lung results in airlessness of all or part of the lung tissue; causes lung tissue density to increase
bronchiectasis
chronic dilation of all the bronchi can result in peribronchial thickening and small areas of atelectasis; causes an increase in lung tissue density
cardiomegaly
an enlargement of the heart causes an increase in thickness of the part
congestive heart failure
when heart is in failure, the cardiac output is diminished; results in backward failure, or increased venous congestion in the lungs; lung tissue density is increased and the heart is enlarged as well
empyema
pus in the thoracic cavity causes an increase in tissue density
pleural effusions (hemothorax, hydrothorax)
when pleural cavity fills with either blood or serous fluid, it displaces normal lung tissue; results in an increased tissue density within thoracic cavity
pneumoconiosis
inhalation of dust particles can cause fibrotic (scarring) changes; when healthy lung tissues become fibrotic, then density of the tissue increases
pneumonectomy
removal of a lung will cause the affected side to demonstrate an increase in IR exposure because normal air-filled lung tissue is removed
pneumonia (pneumonitis)
inflammation of the lung tissues causes fluid to fill in the alveolar spaces; fluid has much greater tissue density than the air normally present
pulmonary edema
when fluid fills the interstitial lung tissues and the alveoli, the tissue density increases; a typical complication of congestive heart failure
tuberculosis (advanced and miliary)
an infection by a mycobacteria causes the inflammatory response, which results in an increase in fluid in the lungs; if inhaled, generally begins as a localized lesion (usually upper lobes) and can spread to a more advanced stage; if reached lungs by bloodstream, it has a more diffuse spread (miliary TB); increased tissue density results in both advanced and miliary TB
additive conditions of the abdomen
aortic aneurysm, ascites, calcified stones, and cirrhosis
pathological conditions of the abdomen will usually cause
abdomen to distend
aortic aneurysm
a large dilation of the aorta will result in increased thickness of the affected part
ascites
fluid accumulation within the peritoneal cavity causes an increase in tissue thickness; free fluid has a unique “ground glass” appearance radiographically
calcified stones
most commonly found throughout the abdomen in such organs as the gallbladder and kidney; calcium may be deposited, which causes an increase in effective atomic number of tissue
cirrhosis
fibrotic changes in the liver cause the liver to enlarge and ascites can result; result is an increase in thickness of the liver and the entire abdomen
additive conditions of the extremities and skull
osteoblastic, acromegaly, chronic osteomyelitis, hydrocephalus, osteoblastic metastases, Paget’s disease, sclerosis
osteoblastic
conditions that result in new bone growth
acromegaly
an overgrowth of hands, feet, face, and jaw as a result of hypersecretion of growth hormones in the adult will result in an increase in bone mass
chronic osteomyelitis
a chronic bone infection results in new bone growth at the infection site
hydrocephalus
a dilation of the fluid-filled cerebral ventricles causes an enlargement of the head, resulting in an increased thickness
osteoblastic metastases
spread of cancer to bone can result in uncontrolled new bone growth
osteochondroma
a tumor arising in the bones and cartilage will result in an increased thickness of bone
Paget’s disease (osteitis deformans)
an increase occurs in bone cell activity, which leads to new bone growth; result is increased bone thickness, with pelvis, spine and skull most often affected
sclerosis
an increase in hardening as a result of a chronic inflammation of bone; increases density of bone tissue
a decrease in what percent of mAs will compensate for most destructive pathological conditions
25%-50%
destructive conditions affecting multiple sites
anorexia nervosa, atrophy, and emanciation
anorexia nervosa
a psychological eating disorder that results in an extreme weight loss; overall body thickness is reduced
atrophy
a wasting away of body tissue with diminished cell proliferation, resulting in reduced thickness of a specific part or the entire body
emanciation
a generalized wasting away of body tissue, resulting in reduced thickness of the body
destructive conditions of the chest
emphysema and pneumothorax
emphysema
overdistention of the lung tissues by air will result in a decrease in lung tissue density
pneumothorax
free air in the pleural cavity displaces normal lung tissue and results in decreased density within the thoracic cavity
destructive conditions of the abdomen
aerophagia and bowel obstruction
aerophagia
a psychological disorder resulting in abdominal swallowing of air; stomach becomes dilated from air and overall tissue density decrease
bowel obstruction
an obstruction in the bowel results in abnormal accumulation of air and fluid; if large amount of air is trapped in the bowel, the overall density of tissues is decreased
destructive conditions of the extremities and skull
osteolytic, active osteomyelitis, aseptic necrosis, carcinoma, degenerative arthritis, fibrosarcoma, gout, hyperparathyroidism, multiple myeloma, osteolytic metastases, osteomalacia, osteoporosis
osteolytic
conditions that result in destruction of bone tissue
what percentage of bone substance must be lost before changes can be seen radiographically
50%
active osteomyelitis
with a bone infection, there is initially a loss of bone tissue (containing calcium), resulting in a decrease in the thickness and composition of the part
aseptic necrosis
death of bone tissue results in a decrease in the thickness and composition of the part
carcinoma
malignancies in bone can cause an osteolytic process, resulting in decreased thickness and composition of the part
degenerative arthritis
inflammation of the joints results in a destruction of adjoining bone tissue, which decreases the composition of the part
fibrosarcoma
malignant tumor of the metaphysis of bone causes an osteolytic lesion with a “moth-eaten” appearance; result is reduced bone composition
gout
during the chronic stages of this metabolic disease, areas of bone destruction result in punched-out lesions that reduce the bone composition
hyperparathyroidism
oversecretion of the parathyroid hormone causes calcium to leave bone and enter the bloodstream; bone becomes demineralized and composition is decreased
multiple myeloma
malignant tumor arises from plasma cells of bone marrow and causes punched-out osteolytic areas on the bone; often many sites are affected and reduced bone tissue composition results
osteolytic metastases
when some malignancies spread to bone they produce destruction of the bone, resulting in reduced composition
osteomalacia
a defect in bone mineralization results in decreased composition of the affected bone
osteoporosis
a defect in bone production due to the failure of osteoblasts to lay down bone matrix results in decreased composition of affected bone
