Pulmonary emboli imaging with (99m)Tc-labelled anti-D-dimer (DI-80B3) Fab' followed by SPECT

SPECT Ventilation/Perfusion Imaging for Acute Pulmonary Embolism: Meta-analysis of Diagnostic Test Accuracy

RATIONALE AND OBJECTIVES

This study aimed to evaluate the diagnostic accuracies of ventilation/perfusion-single photon emission computed tomography (V/Q-SPECT) imaging modalities for acute pulmonary embolism (PE). These included, in addition to V/Q-SPECT, V/Q-SPECT with low-dose computed tomography (CT; V/Q-SPECT-CT), Q-SPECT with low-dose CT (Q-SPECT-CT), and Q-SPECT.

MATERIALS AND METHODS

PubMed, Embase, CINAHL, and Web of Science databases were searched, and studies included if they studied ≥10 adult participants with acute PE and reported data on the imaging tests' diagnostic performance. Data were meta-analyzed using bivariate random effects regression model.

RESULTS

Data from participants totaling 4146 from 11 V/Q-SPECT studies, 785 from 7 V/Q-SPECT-CT studies, 1196 from 7 Q-SPECT-CT studies, and 728 from five Q-SPECT studies were separately meta-analyzed. The bivariate weighted mean sensitivity and specificity were 0.94 (95% confidence interval [CI]: 0.88-0.97) and 0.95 (95% CI: 0.87-0.98) for V/Q-SPECT, 0.95 (95% CI: 0.88-0.98) and 0.99 (95% CI: 0.92-1.00) for V/Q-SPECT-CT, 0.92 (95% CI: 0.79-0.97) and 0.92 (95% CI: 0.83-0.96) for Q-SPECT-CT, and 0.89 (95% CI: 0.76-0.95) and 0.86 (95% CI: 0.67-0.95) for Q-SPECT studies. The positive and negative likelihood ratios (+LRs and -LRs) were 17.4 (6.9-44.0) and 0.06 (0.03-0.13), 76.7 (11.8-498.0) and 0.06 (0.02-0.13), 11.0 (5.3-22.9) and 0.09 (0.04-0.23), and 6.4 (2.6-15.8) and 0.13 (0.07-0.27) for V/Q-SPECT, V/Q-SPECT-CT, Q-SPECT-CT, and Q-SPECTs, respectively.

CONCLUSION

In the diagnosis of acute PE, this meta-analysis showed that V/Q-SPECT-CT had the highest specificity and +LR. Conversely, Q-SPECT showed the lowest specificity and an unfavorably high -LR.

An unmet clinical need: The history of thrombus imaging

Robust thrombus imaging is an unresolved clinical unmet need dating back to the mid 1970s. While early molecular imaging approaches began with nuclear SPECT imaging, contrast agents for virtually all biomedical imaging modalities have been demonstrated in vivo with unique strengths and common weaknesses. Two primary molecular imaging targets have been pursued for thrombus imaging: platelets and fibrin. Some common issues noted over 40 years ago persist today. Acute thrombus is readily imaged with all probes and modalities, but aged thrombus remains a challenge. Similarly, anti-coagulation continues to interfere with and often negate thrombus imaging efficacy, but heparin is clinically required in patients suspected of pulmonary embolism, deep venous thrombosis or coronary ruptured plaque prior to confirmatory diagnostic studies have been executed and interpreted. These fundamental issues can be overcome, but an innovative departure from the prior approaches will be needed.

New developments and future challenges of nuclear medicine and molecular imaging for pulmonary embolism

Although widely validated, current tests for pulmonary embolism (PE) diagnosis, i.e. computed tomography pulmonary angiography (CTPA) and V/Q planar scintigraphy, have some limitations. Drawbacks of CTPA include the radiation dose, some contra indications and a rising concern about a possible overdiagnosis/overtreatment of PE. On the other hand, V/Q planar scintigraphy has a high rate of non-diagnostic tests responsible for complex diagnostic algorithms. Since the PIOPED study, imaging equipment and radiopharmaceuticals have greatly evolved allowing the introduction of techniques that improve imaging of lung ventilation and perfusion. Single photon emission computed tomography (SPECT) and SPECT/CT techniques are already largely used in daily practice and have been described to have greater diagnostic performance and much fewer non-diagnostic tests as compared with planar scintigraphy. However, they have not yet been firmly validated in large scale prospective outcome studies. More recently, it has also been proposed to image pulmonary perfusion and ventilation using positron emission tomography (PET), which has an inherent technical superiority as compared to conventional scintigraphy and may provide new insight for pulmonary embolism. Regardless of modality, these new thoracic imaging modalities have to be integrated into diagnostic strategies. The other major challenge for venous thromboembolism diagnosis may be the potential additional value of molecular imaging allowing specific targeting of thrombi in order, for example, to differentiate venous thromboembolism from tumor or septic thrombus, or acute from residual disease. In this article, the new imaging procedures of lung ventilation perfusion imaging with SPECT, SPECT/CT and PET/CT are discussed. We also review the current status and future challenge of molecular imaging for the in vivo characterization of venous thromboembolism.

SPECT imaging of fibrin using fibrin-binding peptides

Noninvasive detection of fibrin in vivo using diagnostic imaging modalities may improve clinical decision-making on possible therapeutic options in atherosclerosis, cancer and thrombus-related pathologies such as pulmonary embolism and deep venous thrombosis. The aim of this study was to assess the potential of a novel (111)In-labeled fibrin-binding peptide (FibPep) to visualize thrombi in mice noninvasively using single-photon emission computed tomography (SPECT). FibPep and a negative control peptide (NCFibPep) were synthesized and their fibrin-binding properties were assessed in vitro. FibPep showed enhanced binding compared with NCFibPep to both fibrin and blood clots. FibPep bound to fibrin with a dissociation constant (K(d)) of 0.8 μ m, whereas NCFibPep displayed at least a 100-fold lower affinity towards fibrin. A FeCl3 -injury carotid artery thrombosis mouse model was used to evaluate the peptides in vivo. FibPep and NCFibPep displayed rapid blood clearance and were eliminated via the renal pathway. In vivo SPECT imaging using FibPep allowed clear visualization of thrombi. Ex vivo biodistribution showed significantly increased uptake of FibPep in the thrombus-containing carotid in comparison to the noninjured carotid (5.7 ± 0.7 and 0.6 ± 0.4% injected dose per gram (%ID g(-1)), respectively; p < 0.01; n = 4), whereas nonspecific NCFibPep did not (0.4 ± 0.2 and 0.3 ± 0.0%ID g(-1), respectively; n = 4). In conclusion, FibPep displayed high affinity towards fibrin in vitro and rapid blood clearance in vivo, and allowed sensitive detection of thrombi using SPECT imaging. Therefore, this particular imaging approach may provide a new tool to diagnose and monitor diseases such as atherosclerosis and cancer.

Accuracy and safety of (99m)Tc-labeled anti-D-dimer (DI-80B3) Fab' fragments (ThromboView®) in the diagnosis of deep vein thrombosis: a phase II study

BACKGROUND

The assessment of patients with suspected deep vein thrombosis (DVT) remains challenging despite current diagnostic algorithms. (99m)Tc-labelled DI-DD3B6/22-80B3 Fab´ fragments ((99m)Tc-DI-80B3, ThromboView®) is a novel diagnostic test that uses a radiolabelled humanized monoclonal antibody fragment specific for the D-dimer region of cross-linked fibrin to detect DVT. This test has an anatomic component to locate DVT and a functional component to differentiate acute (newly formed) thrombus from inactive (old) thrombus.

METHODS

In a multi-centre prospective cohort trial we investigated the diagnostic accuracy and safety of (99m)Tc-DI-80B3 in consecutive patients with suspected DVT who had the diagnosis confirmed or excluded by venography.

RESULTS

We enrolled 94 patients with suspected DVT of whom 12 did not have (99m)Tc-DI-80B3 imaging, leaving 82 patients for the safety analysis. Of these patients, there were 16 with non-evaluable imaging (11 venography, 7 (99m)Tc-DI-80B3, both in two patients) leaving 66 patients for the accuracy analysis. (99m)Tc-DI-80B3 imaging was well-tolerated: 2 patients developed urticaria; none developed serious adverse events. For proximal DVT, the sensitivity (84.2%; 95% confidence interval [CI]: 62.4-94.5) and specificity (97.6%; CI: 83.3-99.4) were highest when the combined 0.25-hour and 3-hour (99m)Tc-DI-80B3 images were used. The accuracy was lower for distal DVT, irrespective of the images used. There were insufficient patients to comment on the accuracy of (99m)Tc-DI-80B3 imaging for suspected recurrent DVT.

CONCLUSIONS

(99m)Tc-DI-80B3 (ThromboView®) is a novel diagnostic modality for patients with suspected DVT with a promising accuracy and safety profile that justifies additional clinical development in diagnostic accuracy and clinical management studies.

Detection of pulmonary emboli with 99mTc-labeled anti-D-dimer (DI-80B3)Fab' fragments (ThromboView)

RATIONALE

We report a new method to diagnose acute pulmonary embolism (PE) by single photon emission computerized tomography (SPECT) after administration of (99m)Tc-labeled anti-D-dimer (DI-80B3) monoclonal antibody Fab' fragments. This novel technique provides an additional approach to diagnosing PE in patients for whom other methods are nondiagnostic or contraindicated.

OBJECTIVES

We performed a prospective, multicenter study to investigate the sensitivity and specificity of (99m)Tc-DI-80B3/SPECT in patients with suspected acute PE.

METHODS

Subjects with a moderate to high clinical probability of PE or a positive D-dimer test underwent a PE-protocol contrast-enhanced multidetector thoracic computed tomography (CT) scan as well as (99m)Tc-DI-80B3/SPECT (0.5 mg (99m)Tc-DI-80B3 intravenously followed by a thoracic SPECT 2.5 h later). Separate and independent adjudication committees, blinded to clinical data and other test results, interpreted the (99m)Tc-DI-80B3/SPECT scans (PE detected as foci of abnormally increased (99m)Tc uptake) and the thoracic CT scans using Prospective Investigation of Pulmonary Embolism Diagnosis II criteria.

MEASUREMENTS AND MAIN RESULTS

Of the 52 patients who were enrolled and completed both tests, 42 had both evaluable SPECT scans and thoracic CT scans. Using the criterion standard (thoracic CT scan) there were 21 patients with PE and 21 without. (99m)Tc-DI-80B3/SPECT had a sensitivity of 76.2% (95% confidence interval, 52.8-91.8%) and a specificity of 90.5% (95% confidence interval, 69.8-98.8%). Treatment-related serious adverse events did not occur.

CONCLUSIONS

(99m)Tc-DI-80B3/SPECT was sensitive and specific for acute PE in subjects with moderate to high clinical probability of PE or a positive D-dimer test. (99m)Tc-DI-80B3/SPECT demonstrated an acceptable safety profile and avoids exposure to contrast.