Diagnostic evaluation of radioimmunoscintigraphy (RIS) with use of iodine 123-labeled antibodies against human granulocytes (123I-anti-NCA95) for the detection of prosthetic vascular graft infection

Imaging Modalities for the Diagnosis of Vascular Graft Infections: A Consensus Paper amongst Different Specialists

Vascular graft infection (VGI) is a rare but severe complication of vascular surgery that is associated with a bad prognosis and high mortality rate. An accurate and prompt identification of the infection and its extent is crucial for the correct management of the patient. However, standardized diagnostic algorithms and a univocal consensus on the best strategy to reach a diagnosis still do not exist. This review aims to summarize different radiological and Nuclear Medicine (NM) modalities commonly adopted for the imaging of VGI. Moreover, we attempt to provide evidence-based answers to several practical questions raised by clinicians and surgeons when they approach imaging in order to plan the most appropriate radiological or NM examination for their patients.

Diagnosing prosthetic vascular graft infection with the antigranulocyte antibody 99mTc-fanolesomab

AIM

The objectives of this retrospective investigation were to determine the accuracy of 99mTc-fanolesomab, an antigranulocyte antibody, for diagnosing prosthetic vascular graft infection, ascertain optimum imaging times for this indication, and assess safety of this agent.

METHODS

Eighteen patients with 19 prosthetic vascular grafts were included. Indications for graft placement included peripheral vascular disease (8), haemodialysis (7), and aneurysm (4). Patients were imaged 2-5 h and 18-30 h after injection of 555-740 MBq (75-125 microg) 99mTc-fanolesomab. One experienced nuclear physician reviewed images in three separate sessions, early alone, late alone and early plus late images together. When early and late images were read alone, graft activity more intense than native blood pool activity was classified as positive for infection. When early and late images were interpreted together, graft activity which persisted or which increased in intensity over time was classified as positive for infection. Patient records were reviewed for adverse events up to 30 days after injection.

RESULTS

Five (26%) prosthetic grafts were infected. Early, late and early plus late imaging were equally sensitive (1.00). Early images were significantly less specific (0.50), than late and early plus late images (0.93) (P<0.05, analysis of proportions). Accuracy of late imaging and early plus late imaging were the same: 0.93. No patient experienced adverse events following radiopharmaceutical injection.

CONCLUSIONS

99mTc-fanolesomab imaging, performed 18-30 h after injection, diagnosed prosthetic vascular graft infection safely and accurately (95%). (Although safety was not an issue in this investigation, following reports of serious, including two fatal, events after administration, 99mTc-fanolesomab was withdrawn from the United States market).

Nuclear medicine imaging of inflammatory/infective disorders of the abdomen

Different nuclear medicine modalities are currently used to study inflammatory and infective disorders of the abdomen. They are usually complementary to radiology and endoscopy, but they play a pivotal role in particular clinical situations. Several radiopharmaceuticals (e.g., 111In or 99mTc labelled white blood cells, monoclonal antibodies, human polyclonal immunoglobulins, 75Ga citrate) are commercially available, but they can not be used indifferently to study abdominal inflammatory disorders. The lack of comparative studies showing the accuracy of each radiopharmaceutical for the study of inflammatory/infective abdominal diseases does not allow the best nuclear medicine technique(s) to be chosen in an evidence-based manner. To this end we performed a meta-analysis of peer reviewed articles published between 1984 and 2004 describing the use of nuclear medicine imaging for the study of inflammatory bowel disorders, appendicitis and vascular graft infections. A guideline for the optimal radiopharmaceutical(s) to be used in each clinical condition and for different aims is provided.

Expression and characterization of anti-NCA-95 scFv (CEA 79 scFv) in a prokaryotic expression vector modified to contain a Sfi I and Not I site

The CEA 79 antibody has been used in bone marrow scintigraphy for the differential diagnosis of skeletal tumors and the evaluation of the bone marrow status of patients with various hematological disorders. The specific localization of radio-labeled CEA 79 antibody in bone marrow depends on its reactivity with NCA-95 (nonspecific cross-reacting antigen-95) present on the surface and in the cytosol of human granulocytes and myelopoietic cells. To make a CEA 79 scFv molecule that would be less immunogenic and more penetrating than the intact mouse immunoglobulin, we constructed a pRSET Sfi I/Not I expression vector. The scFv gene was then excised from a pCANTAB 5 E phage display vector by digestion with Sfi I and Not I and inserted into the pRSET Sfi I/Not I expression vector. Upon transformation of a BL21(DE3)pLysS strain of E. coli, CEA 79 scFv became expressed in inclusion bodies requiring a renaturation process for solubilization. The final yield of CEA 79 scFv was 5 mg per a liter of culture. The refolded CEA 79 scFv exhibited an affinity (Kd = 2.1 x 10(-9) M) equivalent to that of the original CEA 79 antibody (K(d) = 3.3 x 10(-9) M) and the same immunoreactivity to CEA and NCA-95 in Western blots and in immunohistochemical staining experiments.

Postoperative graft incorporation after aortic reconstruction--comparison between computerised tomography and Tc-99m-HMPAO labelled leucocyte imaging

Aortic graft infection may result in high mortality ranging up to 88%. Therefore, early diagnosis is imperative in the treatment of this serious complication. Computerised tomography (CT) is considered as a sensitive tool in the diagnosis of aortic graft infection. Some findings used as the criteria for infection, such as periprosthetic gas and fluid are, however, normal postoperative findings. The aim of this prospective study was to compare CT-scan and Tc-99m-HMPAO labelled leucocytes in the early diagnosis of aortic graft infection. The present study includes 24 consecutive patients (all men, age 70 +/- 8 years, range 55-85 years), who were operated on for abdominal aortic aneurysm. Prosthetic and suture materials were the same in all operations. Each patient was examined with the aid of CT-scan and imaged with Tc-99m-HMPAO labelled leucocytes 2 weeks and 3, 6 and 12 months after the reconstructive aortic surgery. Two radiologists and two specialists in nuclear medicine examined the data independently without knowing the clinical picture of the results of any other examinations of the patients. Seven patients (7/24; 29%) showed significant accumulation of labelled leucocytes in the first imaging (2 weeks postoperatively) with Tc-99m-HMPAO labelled leucocytes. Three months after the surgery only four patients (4/24; 17%) were positive in this respect. One of these patients had clinically proven aortic graft infection and another positive was a patient with resected and reconstructed mycotic aneurysm. CT-examination in all scans was suggestive for aortic graft infection in two cases (2/24; 8%), but neither of these patients showed any signs of infection.(ABSTRACT TRUNCATED AT 250 WORDS)