The interpretation of phlebograms using fibrinogen labeled with 99 mTc

Non-Invasive Screening for Deep Vein Thrombosis: Comparison between 99mTc-labelled Compounds, Thermography, 131 I-Fibrinogen Uptake Test and X-Ray Phlebography

In 81 patients with clinically suspected deep vein thrombosis, the diagnostic accuracy of thermography, 99m Tc-plasmin and 99m Tc-fibrinogen uptake tests for detecting and localizing DVT was compared with a routinely used 131 I-FUT and X-ray phlebography as reference method. Sensitivity of these tests for detection of DVT was high (0.86–1.0). 99m Tc-labelled compounds and thermography should be used for detecting rather than for localizing DVT, since sensitivity of these tests was somewhat lower in the thigh. Clinical examination and exclusion of patients with inflammatory processes, hematoma or trauma markedly increases the specificity. Uptake tests with 99m Tc-labelled compounds are fast, reliable and suitable as bedside tests.

In vitro properties and in vivo behavior of technetium-99m labeled fibrinogens

Fibrinogen was labeled with Tc-99m by two methods and in vitro stability and the in vivo behavior in mice were studied. The Tc-99m labeling was performed by mixing an unreduced fibrinogen (UnFib) or a reduced fibrinogen (ReFib) with Tc-99m pertechnetate in the presence of stannous chloride. In both of them, chelation with Tc-99m resulted in a single radiochemical product. For the in vitro stability studies, Tc-99m labeled fibrinogen (Tc-99m UnFib) was prepared with UnFib, and transchelation with cysteine solution was easy to produce compared to Tc-99m labeled fibrinogen (Tc-99m ReFib) prepared with ReFib. The radioactivity bound to clottable protein for Tc-99m UnFib and Tc-99m ReFib was about 70% and about 69%, respectively. The in vivo behavior of these labeled fibrinogens was studied, and their efficiencies for imaging an abscess and Ehrlich tumor in mice were determined with a gamma camera. Technetium-99m UnFib underwent a rapid partial exchange of the Tc-99m with compounds of the blood buffer system in vivo, resulting in early biologically active and would be incorporated into the abscess and tumor. The uptake in the abscess increased slightly over time with Tc-99m ReFib, but the abscess to blood and abscess to muscle ratios were 0.09 and 2.6 at 5 hr, respectively. Clearly delineated images of abscess were obtained beginning at about 5 hr after injection. The tumor to blood and tumor to muscle ratios were 0.05 and 1.4 at 5 hr, respectively. The Ehrlich tumor image in mice was slightly visible at 10 hr. The short half-life of Tc-99m was inappropriate for fibrinogen with a low pharmacokinetic value, because it was necessary for imaging of the abscess and tumor to take a long time.

Radiopharmaceuticals for thrombus detection

Most of the components of the thrombotic and fibrinolytic systems have at some time been evaluated as a means of carrying a radiolabel specifically to thrombi, although very few have been promising enough to emerge from investigational status to routine clinical use. New approaches are being explored, including improved methods of labeling platelets, chemically modified forms of previously tested plasma proteins, and new biomolecules, including monoclonal antibodies specific for fibrin and platelets. The current goal is to find one or more radiotracers that bind specifically and rapidly to thrombi, and that also have a rapid blood disappearance rate, permitting a clear diagnosis within a few hours after injection. Because this test may be needed to assess the course of therapy in an anticoagulated patient, the ideal radiopharmaceutical should be able to locate thrombi without interference by anticoagulants. Until a suitable thrombus-specific radiopharmaceutical becomes generally available, many hospitals will continue to attempt to make a diagnosis with nonspecific radiopharmaceuticals that can at best provide blood pool images to indicate filling defects. Several of the new approaches seem likely to provide the radiopharmaceutical sought, although clinical trials are at an early stage.

A comparison of radiolabelled agents for thrombus imaging using a rabbit model

The quantitative uptakes of five potential thrombus-localizing radiopharmaceuticals in experimental thrombi of the rabbit jugular vein have been compared to assist with the selection of a thrombus imaging agent for clinical use. Three hours after injection, 111In-platelets were clearly the agent of choice but at 18 h 99mTc-fibrinogen had more favourable characteristics. Both agents were superior to 99mTc-plasmin or its acyl derivatives, including 99mTc-streptokinase-activated anisoylplasminogen. The ease of preparation coupled with favourable biological properties suggest that 99mTc-fibrinogen should be of value in the clinical situation.

Diagnosis of deep-vein thrombosis: comparison of clinical evaluation, ultrasound, plethysmography, and venoscan with X-ray venogram

In 50 patients with suspected deep-vein thrombosis the diagnostic accuracy of standardised clinical examination, doppler ultrasound, impedance plethysmography, and technetium-99m-labelled-fibrinogen scintigraphy (venoscan) was compared with that of X-ray venography. Physical examination was the least accurate method. Impedance plethysmography, venoscan, and ultrasound had accuracies of 65%, 80%, and 82%, respectively. The initial X-ray venogram report had an accuracy of 90% compared with the interpretation of two experienced radiologists. The venoscan was equivocal in 32% of patients, and in the remaining patients the accuracy was 97%. Objective methods of investigation are essential for diagnosing deep-vein thrombosis. Of those tested, the X-ray venogram was the only investigation suitable for definitive diagnosis. The venoscan may have a role as a screening procedure, to be followed by X-ray venography in patients with equivocal venoscan results.

Kinetics of [99mTc]heparin, venous scintigraphy with [99mTc]fibrinogen and beta-thromboglobulin assay in the diagnosis of deep-vein thrombosis

The information provided by three examinations: [99mTc]heparin kinetics (KH), venous scintigraphy with [99mTc]fibrinogen (VSF) and plasmatic assay of beta-thromboglobulin (beta TG), are studied on 23 patients separated into two groups on the basis of phlebographic results. VSF which could provide to a certain extent the same kind of information as phlebography, proves to have insufficient sensitivity. KH has high specificity but low sensitivity, while beta TG performance is the opposite. The authors discuss the mechanisms responsible for these discordant results. They observe that in cases where the KH and beta TG correspond, the diagnostic value is very satisfactory, so that a double positive can replace phlebography in cases where the latter is contra-indicated or difficult to perform.