Avoiding False‐Positive Joint Scans by the Use of Labeled Albumins

Abstract

Knee joints were scanned in a group of patients with gout and rheumatoid arthritis and in a second group of patients without joint disease. 1311 human serum albumin, 99mTc-albumin or 99mTc-pertechnetate were utilized. Scans performed with labeled albumin were reliable indicators of the presence or absence of active inflammation of the joint. Technetium, as the pertechnetate, not only concentrated in all inflamed joints but was also concentrated in the knee joint of 19 of 20 patients without joint disease.A number of reports have recently appeared on the clinical usefulness of 99nlTc as the pertechnetate in photoscanning joints in patients with arthritis (1-5). Photoscans of the joints were originally performed by Maxfield (6,7) using l3lI human serum albumin. Sodium pertechnetate offers the advantages 1311 of lower radiation to the patient and greater speed i n photoscanning. T h e mechanism whereby these two agents localize in the joints is not definitely known, but it has been suggested that they are different ( 1 4 ) . Studies have been initiated in our laboratory to compare these two agents plus QQmTc human albumin and to determine their mechanism of localization and clinical utility. These studies indicate that 9QmTc, as the pertechnetate, may be associated with an appreciable incidence of false-positive scans, but that this phenomenon is not observed with either of the labeled albumins. MATERIALS AND METHODSAll patients were scanned with a multiprobe scannert using a medium focusing collimator with a 4-inch focal distance and a 2.7-inch depth response for technetium and a coarse focusing collimator with a 5-inch focal distance and a 3.2-inch depth response for iodine. Other instrument settings varied, depending on the count rate and the isotope being used (Table 1 ) . All scans were set up by "peaking-in" over the mid-portion of the patella. Selected studies were repeated on a 3-inch rectilinear scanner$ or a scintillation camera.5 Scintiphotographs were obtained by collecting 200,000 counts from each knee. '=I human serum albumin cmI HSA) was administered intravenously in a dose of 25

The pertechnetate joint scan. II. Clinical correlations.

“…In these normal subjects, some minimal differences in pattern were seen but, with experience, these could easily be distinguished from the joint abnormalities seen in arthritic patients. Our experience, therefore, differed from that of Cohen and Lorber (1971). Although the official reading for purposes of this study was done by one observer, subsamples read independently by another observer were in excellent agreement.…”

The pertechnetate joint scan. I. Timing.

“…On the other hand, there has been disagreement about the proper time to examine large joints such as the knee. Cohen and Lorber (1971) have recently shown that, when scanning is performed with pertechnetate rather than with an albumin-attached isotope, falsepositive knee scans may be seen after an interval of 1 to 2 hrs. It is possible that the increased identification of inflamed knees observed by other workers after prolonged delay (McCarty and others, 1969) represent an accumulation of radioactivity in the synovial fluid, which is slow to reach equilibration with the serum.…”

Bone Scanning in Clinical Practice

“…The vascular compartment markers, viz. 131 1 albumin, 131 1 iodipamide (Maxfield et al 1968), radiopertechnetate (Hays and Green 1972), 99 m Tc albumin (Cohen and Lorber 1971), Il3mln (Martinez-Villesenor and Katon 1968) and 99mTc_ DTP A (Maxfield et al 1972) 2. Bone seekers, viz.…”