J Nucl Med 16:1013-1016, Nov 1975. Treves S, Khettry J, Broker FH, et al: Osteomyelitis: Early scintigraphic detection in children. Pediatrics 57:173-186, Feb ...
EPITOMES-NUCLEAR MEDICINE
imaging of the hips allows comparison of right and left hip activities. Perfusion is considered absent if activity in the region of the femoral neck is below adjacent body background, probably present if activity equals background, and normal for increased activities. Bone activity is considered normal if activity in the region of the femoral head is equal to, or only slightly greater than, surrounding bone activity. Abnormal activity may be less than, or distinctly greater than, surrounding bone activity. Changes from a baseline value are also considered significant. Infarcted bone undergoes a sequence of changes. Acutely there is simply the avascularity (negative area on bone scan); after several days there is an increasing osteoblastic reactivity surrounding the ischemic-avascular bone (bone scans become increasingly positive) over a period of weeks. The BM image shows decreased perfusion of the neck during the entire sequence. If revascularization occurs, commonly seen in LeggPerthes disease, the BM study will show increasing activity and the bone study will return to normal. Therefore, in patients with chronic avascular necrosis there will be a negative BM image and a positive bone image. This pattern would be expected also with trauma, sickle cell crises and tumors (and probably osteomyelitis). On the other hand, in a patient with osteoarthritis, frequently the major differential diagnosis in hip pain, there will be parallel changes in bone and BM activity, both increasing if there is active inflammation, both decreasing if there is relative disuse of the involved joint. NANCY TELFER, MD REFERENCES Danigelis JA: Pinhole imaging in Legg-Perthes disease, In Sutzker LG, Alavi A: Bone and marrow imaging in sickle cell disease: Diagnosis of infarction. Semin Nucl Med 6:69, 83, Jan
1976 Sy WM, Westring DW, Weinberger G: "Cold" lesions on bone imaging. J Nucl Med 16:1013-1016, Nov 1975 Treves S, Khettry J, Broker FH, et al: Osteomyelitis: Early scintigraphic detection in children. Pediatrics 57:173-186, Feb 1976
Serum Ferritin FERRITIN, the second most abundant iron protein in the body, can be measured in serum by means of a radioimmunoassay. Serum levels are proportional to the size of the tody iron stores. They are more accurate indicators of iron deficiency than serum levels of iron or iron binding capacity or bone marrow aspirates stained for hemosiderin. As expected, mean values are higher in
men than in women, but in either case-and regardless of age-serum values under 12 ng per ml are almost invariably diagnostic of iron deficiency. Levels above 50 ng almost always exclude iron deficiency in the differential diagnosis of anemias. Each ferritin molecule is thought to consist of a ferric iron hydroxide phosphate core and a protein shell with a molecular weight of about 450,000. Found mainly in the cytoplasmn of reticuloendothelial and liver cells, it is assumed to be an iron storage protein and regulator of iron metabolism. From a practical standpoint, the finding of an elevated serum ferritin level in an anemic patient would exclude iron deficiency and might obviate the need for bone marrow examination. JORGE FRANCO, MD REFERENCES Lipschitz DA, Cook JD, Finch CA: A clinical evaluation of serum ferritin as an index of iron stores. N Engl J Med 290: 1213-1216, May 1974 Jacobs A, Worwood M: Ferritin in serum. Clinical and biochemical implications. N Engl J Med 292:951-956, May 1975
Lung Scanning and the Detection of Pulmonary Emboli Combined 81 m-Krypton Ventilation/99m-Tc-macroag-
gregate Perfusion Scintigraphy INTRAVENOUSLY INJECTED PARTICLES whose diameters range from 15 to 50 ji are carried through the right atrium and ventricle, and distribute themselves over the lung capillaries according to blood flow distribution. In the capillaries they remain trapped for an average of 30 minutes to 4 hours. If the particles are labeled with a gamma emitting isotope, the distribution of the blood flow to the lungs can be estimated by scintigraphy. therefore, perfusion abnormalities can be detected as "defects" in the scintigram. But do perfusion defects represent pulmonary emboli? Not always, and the question has been argued with some passion over the years. Normal findings on perfusion scintigraphy almost eliminate the chance that a pulmonary embolism will be found, but all perfusion defects are not indicative of the presence of pulmonary emboli. On pulmonary angiography, emboli will be found respectively in 81 percent, 50 percent and 9 percent of cases with lobar, segmental and subsegmental defects shown on the perfusion scan. The specificity of the test increases if it can be shown that the corresponding lung lesion has a normal ventilation. In those cases the probability of finding emboli by angiography becomes 94 percent, THE WESTERN JOURNAL OF MEDICINE
489
EPITOMES-NUCLEAR MEDICINE
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Figure 1.-Ventilation perfusion lung scan, posterior view. The top part of the picture shows the perfusion study on the left, the ventilation study on the right. The right diaphragm is elevated. Additionally, multiple segmental defects are seen in the perfusion study, without corresponding abnormalities in the ventilation picture. This is underscored in the pictures at the bottom. On the left a perfusion/ventilation ratio shows the multiple perfusion defects, while on the right a ventilation/perfusion ratio shows that there are no isolated ventilation abnormalities.
100 percent and 50 percent respectively. If the perfusion defects are matched by ventilatory abnormalities, only 11 percent represent an embolus. Recently a new technique has been introduced that greatly simplifies the determination of regional lung ventilation. In this technique a very short-lived (13 seconds) radioactive inert gas (8 1m-krypton) is inhaled by the patient. The short life of the tracer prevents it from reaching less ventilated regions, so that its distribution re-
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flects lung ventilation exactly as the distribution of the particles reflects perfusion. In normal cases the ventilation and perfusion images are very similar. Mismatches between ventilation and perfusion can easily be detected (Figure 1). The new method is less cumbersome than the previous methods and allows the alternating recording of ventilation and perfusion scintigraphies, thus avoiding the need for repositioning. Little
EPITOMES-NUCLEAR MEDICINE
patient cooperation is needed so that the method can be applied to sick persons. Finally, the method appears sensitive enough to weaken the argument that mismatches are in fact due to the lack of sensitivity of the method used to detect regional ventilatory abnormalities. MICHAEL L. GORIS, MD REFERENCES McNeil BJ: A diagnostic strategy uising ventilation-perfusion fcr pulmonary embolism. J Nucl Med suspect patients studies in
17:613-619, Jul 1976 Goris ML, Daspit SG, Walter JP, et al: Applications of ventilation lung scanning with 81m-krypton. Radiology 122:399403, Feb 1977
The Use of Bone Scans in Benign Disease of Bone SIGNIFICANT
ADVANCEMENT
in nuclear medicine
instrumentation and radiopharmaceuticals has resulted in the widespread use of bone scans. A number of excellent publications have stressed the sensitivity and reliability of bone scanning in the detection of occult malignancies. Recent articles also have stressed the value of bone scans in a number of benign conditions. * Acute Osteomyelitis. In patients with bone pain and fever, abnormal findings on bone scan may be the only sign of osteomyelitis. In general, the bone scan in these patients becomes positive within 48 to 72 hours after onset of symptoms. * Trauma. Bone scanning has been shown to be a sensitive indicator of trauma to the skeletal system. Not only are major bone fractures visualized, but small stress fractures that are x-ray negative may be seen. * Paget Disease. The extent of Paget disease can be readily determined from the use of total body bone scans. The response to therapy may also be studied and quantitated using scanning techniques and computers. * Benign Tumors. Benign bone tumors such as osteoid osteomas can be detected using conventional bone scanning techniques. * Joint Disease. Scanning of the arthritides, especially rheumatoid arthritis and osteoarthritis, as well as septic arthritis, is useful in determining the site as well as the extent of involvement. * Other Diseases of Bone. Bone scanning coupled with marrow scanning has proven to be of value in the assessment of bony infarction, Legg-Perthes disease, metabolic disease of bone and other less common diseases of the skeletal system. In summary, recent advances in radiopharmaceuticals and instrumentation have made possible
the evaluation of a number of benign diseases of the skeletal system with a low degree of radiation exposure, and high degree of reliability and safety. ALAN D. WAXMAN, MD REFERENCES O'Mara RE: Bone scanning in osseous metastatic disease. JAMA 229:1915-1917, Sep 30, 1974 Merrick MV: Bone scanning. Br J Radiol 48:327-351, May 1975
Soft Tissue Accumulation of Bone Scanning Agents SCINTIGRAPHY with various technetium-phosphate compounds (TcP) is very useful in the diagnosis of benign and malignant bone disease, and its superior sensitivity compared with radiography is well documented. Like any medical technique, however, it has its shortcomings. These include lack of specificity, occasional false-negative results and also extraosseous radiopharmaceutical localization, which may or may not interfere with interpretation of the study. While not all causes for soft-tissue uptake are known, a number have been described. They include: * Physiologic concentration in the urinary tract, since TcP is excreted by this route. This permits, from time to time, detection of unsuspected genitourinary pathology. * Poor quality of the radiopharmaceutical, leading to concentration of free technetium in thyroid and stomach or to colloid aggregation and phagocytic uptake in liver and spleen. * Increased tissue calcium levels, as in necrotic and acutely damaged muscle and in some calcifying neoplasms and granulomas (sarcoid). The high TcP concentration in acutely infarcted myocardium has been turned to advantage for detection and localization of acute myocardial infarcts. Even slight skeletal muscle damage, due to repeated intramuscular injections, may result in prominent TcP deposition. * For reasons still unknown, normal breast tissue and a number of soft tissue tumors without demonstrated abnormalities in calcium metabolism will also concentrate TcP, particularly- carcinoma of the lung, breast and colon and sarcoma. Unusual extraosseous TcP concentration (outside of the genitourinary tract) is seen in about 10 percent of all bone scans. To avoid confusion and unnecessary repetition of procedures, nuclear medicine specialists and referring physicians have to be aware of its occurrence and causes. JAN K. SIEMSEN, MD
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