Pathology and Radiation Absorption in Medical Imaging

1. Chapter 17 The Pathology Problem

2. Pathology and Radiation Absorption • As radiation passes through the patient it undergoes attenuation or absorption of the x-ray photons. • Pathological conditions can affect the overall thickness and composition of the patient’s tissues.

3. Pathology • The medical science that is concerned with all aspects of disease, including the structural and functional changes caused by a disease process. • Certain diseases can increase or decrease tissue thickness or alter tissue composition (change the effective atomic number or density). • The disease will affect the degree of radiation absorption for that specific body tissue. • Example: fluid will absorb more radiation than air.

4. Technical Factor Adjustments • To produce a visible difference requires a minimal change of 25-50 percent in the overall exposure to the image receptor for film/screen radiography. • It is the technologist’s responsibility to keep the patient dose for a given exam as low as possible without compromising image quality.

5. Automatic Exposure Control • AEC systems will compensate for most pathological changes by adjusting the exposure automatically. • The compensation will be the result of increased mAs rather than increased kVp.

6. Additive Conditions • A disease that causes the affected body tissue to increase in thickness, effective atomic number, and/or density. There will be a greater attenuation of the x-ray beam. • More photons are absorbed, fewer will be available to reach the image receptor. • Requires increasing technical factors to achieve the proper image receptor exposure. • Image receptor exposure will decrease as the extent of the disease increases- inverse relationship

7. Additive Conditions • Additive conditions will require an increase in kilovoltage to adequately penetrate the thicker, more opaque body parts. • An increase of 15 percent will approximately double the exposure to the image receptor. • An increase of 5-15 percent in kilovoltage will compensate for most additive pathologic conditions.

8. Conditions affecting Multiple Systems • Abscess: an encapsulated infection increases tissue thickness and may alter composition, particularly in the 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.

9. Conditions of the Chest • Atelectasis: a collapse of the lung results in airlessness of all or part of the lung tissue. This causes lung tissue density to increase. • Bronchiectasis: the chronic dilation of the bronchi can result in peribronchial thickening and small areas of atelectasis. This 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 the heart is in failure, the cardiac output is diminished. This results in backward failure, or increases venous congestion in the lungs. Lung tissue density is increased and the heart is enlarged as well.

10. Conditions of the Chest • Empyema: pus in the thoracic cavity causes an increase in tissue density. • Pleural Effusions (Hemothorax, Hydrothorax): when the pleural cavity fills with either blood or serous fluid, it displaces normal lung tissue, this results in an increased tissue density within the thoracic cavity. • Pneumoconiosis: the inhalation of dust particles can cause fibrotic changes. When healthy lung tissue becomes fibrotic, density of the tissue increases. • Pneumonectomy: the removal of a lung will cause the affected side to demonstrate an increase in density since normal air-filled lung tissue is removed.

11. Conditions of the Chest • 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, tissue density increases. This is 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 the mycobacteria were inhaled, it generally begins as a localized lesion, which can spread to a more advanced stage. If the infection reached the lungs by the bloodstream, it has a more diffuse spread (miliary TB). Increased tissue density results in both TBs.

12. Conditions of the Abdomen • 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. The free fluid has a unique “ground glass” appearance radiographically. • Calcified Stones: stones are most commonly found throughout the abdomen in such organs as the gallbladder and the kidney. Calcium may be deposited, which causes an increase in the effective atomic number of the tissue. • Cirrhosis: fibrotic changes in the liver cause the liver to enlarge and ascites can result. The result is an increase in the thickness of the liver and the entire abdomen.

13. Conditions of the Extremities of the Skull • Conditions that result in new bone growth are termed osteoblastic. • Acromegaly: an overgrowth of the 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 affected site. • Hydrocephalus: a dilation of the fluid-filled cerebral ventricles causes an enlargement of the head, resulting in an increased thickness.

14. Conditions of the Extremities of the Skull • Osteoblastic Metastases: the spread of cancer to bone can result in uncontrolled new bone growth. • Osteochondroma: a tumor arising in the bone and cartilage will result in an increased thickness of the bone. • Paget’s Disease (osteitis deformans): an increase occurs in bone cell activity which leads to new bone growth. The result is increased bone thickness with the pelvis, spine, and skull most often affected. • Sclerosis: an increase in hardening as a result of a chronic inflammation in bone. This increases the density of bone tissue.

15. Destructive Conditions • A disease that causes the affected body tissue to decrease in thickness, effective atomic number, and/or density. There will be less attenuation of the x-ray beam. • More photons are absorbed, more will be available to reach the image receptor. • Requires decreasing exposure to achieve the proper image receptor exposure. • Image receptor exposure will increase as the extent of the disease increases- direct relationship

16. Destructive Conditions • These conditions cause the absorption of less radiation and require a decrease in technical factors to compensate for the changes in body tissue. • Compensations can be made by decreasing the mAs. • A decrease of 50 percent in mAs will reduce the exposure to the image receptor by half. • A decrease of 25-50 percent in mAs will compensate for most of these conditions.

17. Conditions affecting Multiple Systems • Anorexia Nervosa: a psychological eating disorder which 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. • Emaciation: a generalized wasting away of body tissue, resulting in reduced thickness of the body.

18. Conditions of the Chest • Emphysema: the overdistention of the lung tissue 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.

19. Conditions of the Abdomen • Aerophagia: a psychological disorder resulting in abnormal swallowing of air. The stomach becomes dilated from the air and overall tissue density decreases. • Bowel Obstruction: an obstruction in the bowel results in the abnormal accumulation of air and fluid, if a large amount of air is trapped in the bowel, the overall density of the tissues is decreased.

20. Conditions of the Extremities of the Skull • Conditions that result in the destruction of bone tissue are termed osteolytic. • 50 percent of the bone substance must be lost before changes can be seen radiographically. • 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 composition and thickness of the part.

21. Conditions of the Extremities of the Skull • 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: this malignant tumor of the metaphysis of bone causes an osteolytic lesion with a “moth eaten” appearance, the result is reduced bone composition.

22. Conditions of the Extremities of the Skull • Gout: during the chronic stages of the 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. The bone becomes demineralized and composition is decreased. • Multiple Myeloma: this 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.

23. Conditions of the Extremities of the Skull • 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 the affected bone.