Erica A. George

Mechanism of hepatic extraction of gelatinized 99mTechnetium sulfur colloid

Hepatic extraction, cellular and subcellular localization of gelatin stabilized Tc-99m sulfur colloid was studied in the rat model with time sequenced microautoradiography from 15 min to 24 h following I.V. administration of the tracer. Hepatic lobular and cellular distribution, quality and quantity of focal grain pattern, grain clusters, remained essentially constant for the period of study. Grain clusters were associated predominantly with Kupffer cells lining the peripheral segment of hepatic lobular sinusoids. Subcellular localization of gelatinized Tc sulfur colloid, stained prior to the I.V. administration with osmium tetroxide, was demonstrated with a transmission electron microscope in unosmicated liver tissue. Extracted Tc sulfur colloid particles were attached in groups to cytoplasmatic membranous intrasinusoidal projections of activated Kupffer cells. Intracytoplasmatic phagocytosis was not demonstrated. The kinetic arrest and en groupe extraction of Tc sulfur colloid particles at the Kupffer cell membrane suggests a specific membrane receptor site and specific Tc sulfur colloid particle-plasma protein interaction at the time of extraction. Hepatic extraction of gelatinized Tc sulfur colloid thus reflects primarily extra and intra hepatic hemodynamics and does not serve as an indicator of phagocytic hepatic reticuloendothelial system function.

Radionuclide diagnosis of allograft rejection

Interaction with one or more anatomical and physiopathological characteristics of the rejecting renal allograft is suggested by those radioagents utilized specifically for the diagnosis of allograft rejection. Rejection, the most common cause of declining allograft function, is frequently mimicked clinically or masked by other immediate or long term post transplant complications. Understanding of the anatomical pathological features and kinetics of rejection and their modification by immunosuppressive maintenance and therapy are important for the proper clinical utilization of these radioagents. Furthermore, in selecting these radionuclides, one has to consider the comparative availability, preparatory and procedural simplicity, acquisition and display techniques and the possibility of timely report. The clinical utilities of radiofibrinogen, 99mTc sulfur colloid and gallium-67 in the diagnosis of allograft rejection have been evaluated to a variable extent in the past. The potential usefulness of the recently developed preparations of 111In labeled autologous leukocytes and platelets are presently under investigation.

67Ga Citrate in Renal Allograft Rejection

Eight renal allograft recipients were examined on 31 occasions following administration of 99mTc sulfur colloid and 67Ga citrate. Transplant accumulation of each agent was compared and collated with the clinical diagnosis. The procedures matched in 25 instances (81%). Gallium accumulated in the graft producing a false positive result in 2 instances of acute tubular necrosis with anuria, and failed to accumulate within the graft in one case of chronic rejection and in 2 instances of acute rejection. Both radioagents failed to accumulate in 3 patients with acute rejection following heparin therapy. These data indicate that 99mTc sulfur colloid is superior to 67Ga citrate in establishing the diagnosis of transplant rejection and also provides more timely information.

Further Evaluation of 99mTc Sulfur Colloid Accumulation in Rejecting Renal Transplants in Man and a Canine Model1

Renal transplant accumulation of 99m-Tc sulfur colloid was evaluated in 41 patients. Ninety-five examinations were performed comparing transplant with bone marrow activity and clinical or pathological diagnosis. 99m-Tc sulfur colloid accumulated in acute or chronic rejection as long as the vascular supply of the grafted kidney was not severely impaired. Accumulation was marked in chronic rejection, slight in acute rejection and absent in normally functioning transplants or in those with acute tubular necrosis. In the 10 dog models, no accumulation was seen in autografted transplants and early accumulation was demonstrated within the hyperacutely rejecting kidneys of allografted dogs.

Late onset renal allograft anastomotic pseudoaneurysm with absent Doppler signal

A large extrarenal pseudoaneurysm, originating from the arterial anastomosis of a renal allograft, occurred spontaneously 7 years after transplantation in a 29-year-old diabetic patient. Although the scintigraphic examination was diagnostic of a pseudoaneurysm, pulsed Doppler and color coded Doppler ultrasound failed to demonstrate a Doppler signal, suggesting erroneously a nonvascular fluid collection. The role of scintigraphy combined with duplex ultrasound in this rare but potentially fatal complication of renal transplantation is discussed.

Serendipitous Scintigraphic Detection of Asymptomatic Anastomotic Pseudoaneurysms in Human Pancreatic Allografts

Two cases of scintigraphically detected asymptomatic graft anastomotic pseudoaneurysms are reported. Both patients previously underwent simultaneous renal and pancreatic transplantation. The role of imaging in the diagnosis of this relatively rare, but potentially lethal, vascular complication of pancreatic transplantation is discussed. This is the first report of anastomotic pseudoaneurysms in pancreatic transplants being diagnosed by scintigraphy.

Bone marrow 99m Tc sulfur colloid distribution and marrow cellularity.

The relationship between marrow distribution as imaged with 99mTc sulfur colloid and histologic estimate of bone marrow cellularity was examined in 101 patients. The patients were divided into three groups according to marrow cellularity: normocellular, hypercellular or hypocellular marrow. The marrow distribution of these patients was graded as extended, not extended or not visualized. A general association between marrow cellularity and marrow distribution was found. Seventy-seven per cent of patients with normocellular marrow had limitation of marrow within normal sites and a similar number of patients with reactive hypercellular marrow had marrow extension. On analysis of the patients that were exceptions to this generalization the following observations were made. In patients in whom the marrow is hypercellular and infiltrated with abnormal cells or tissue the marrow distribution may not be visualized with radiocolloid. Stimulation of hematopoiesis may result in marrow hypercellularity without marrow extension beyond the usual sites. Stimulation of one or more hematopoietic cell lines may result in marrow extension without marrow hypercellularity, suggesting an impairment of hematopoietic cell response. Peripheral marrow extension as observed with radiocolloid, therefore, is not simply a reflection of marrow hypercellularity but probably represents a response of the bone marrow stroma to situations in which one or more hematopoietic cell lines is stimulated.