⁶⁸Ga PET/CT Ventilation–Perfusion Imaging for Pulmonary Embolism: A Pilot Study with Comparison to Conventional Scintigraphy

Abstract

Ventilation-perfusion (V/Q) scintigraphy is established for regional assessment of lung function in a variety of diseases, including pulmonary embolism (PE). PET/CT may further improve the accuracy and utility of V/Q imaging because of its superior technical characteristics. This pilot study assessed the feasibility of performing V/Q PET/CT and compared diagnostic utility with conventional V/Q imaging in patients with clinical suspicion of PE. Methods: Ten patients undergoing conventional V/Q imaging were prospectively recruited. PET/ CT V/Q imaging was performed after inhalation of 68 Ga-carbon nanoparticles ("Galligas") and administration of 68 Ga-macroaggregated albumin. Blinded to the results of the other study, SPECT/CT (n 5 9) or SPECT (n 5 1) images and PET/CT images were graded by a predefined scoring system for scan quality. The number of matched or unmatched defects and diagnosis were also measured and compared with a final diagnosis. Results: PET image quality was equivalent or superior to SPECT in all patients, with more homogeneous radiotracer distribution for both ventilation and perfusion studies (P , 0.01). Based on conventional V/Q imaging, the diagnosis was acute PE in 2 patients and no PE in 7 patients, and the imaging results were nondiagnostic in 1 patient. The PET/CT diagnosis was concordant in 8 patients, and these studies demonstrated a similar number and distribution of matched and unmatched defects. In 1 discordant case, a patient with a SPECT/CT study that was nondiagnostic because of severe airway disease showed no PE on PET/CT. In another, the diagnosis of PE established on SPECT/CT was not reported on PET/CT 2 d later, possibly because of interval clot lysis or migration. Conclusion: This intraindividual comparative study demonstrated that V/Q PET/CT with 68 Ga-labeled radiotracers can be performed in clinical practice. Compared with conventional V/Q imaging, advantages include higher-resolution, fully tomographic images with potentially better regional quantitation of lung function. The short half-life of 68 Ga also enables more flexible acquisition protocols with the option of performing ventilation studies selectively on patients with abnormal perfusion. On the basis of our results, further studies are indicated to assess whether V/Q PET/CT can improve diagnostic algorithms for patients with suspected PE. Vent ilation-perfusion (V/Q) scintigraphy allows assessment of regional lung function in a variety of diseases. Most studies are performed to assess patients with suspected pulmonary embolism (PE) because presenting symptoms and signs are variable and insufficient for a clinical diagnosis. The Prospective Investigation of Pulmonary Embolism Diagnosis study (1), designed in 1983, established V/Q imaging as the standard of care at the time. V/Q imaging has improved in the past 3 decades because of major advances in image acquisition, reconstruction, and analysis techniques. The use of 99m Tc-labeled carbon nanoparticles (Technegas; Cyclopharm) has improved the assessment of ventil...

Diagnosis of Pulmonary Embolism: Conventional Ventilation/Perfusion SPECT Is Superior to the Combination of Perfusion SPECT and Nonenhanced CT

“…The all-cause mortality rate of patients with unsuspected PE is even higher than the mortality rate of patients with suspected PE [16]. V/P-SPECT and contrast-enhanced CT of the chest are widely used as primary diagnostic methods [6] with sensitivities and specificities greater than 90-95% [3]. However, only limited data are available on the comparison of diagnostic sensitivity and specificity of these two cross-sectional imaging techniques.…”

“…Contrast-enhanced CT is the main investigational method for the diagnosis of PE in Germany (interdisciplinary S2 guidelines [2]) as well as in many other countries [3,4,5]. However, for patients with renal dysfunction, a critical illness or a contrast-medium allergy, applying ventilation/perfusion (V/P) scintigraphy is preferable as there are no contraindications and no reports of allergic reactions [6]. …”

Radio‐Labeled Nanoparticles for Biomedical Imaging

“…This suggests that the high pulmonary retention is most likely due to size exclusion and phagocytosis [135]. In clinical applications, 68 ga-labeled carbon nanoparticles have also been used for pulmonary embolism peT/CT ventilation/ perfusion (V/Q) imaging and have demonstrated superiority to conventional V/Q lung scintigraphy [136].…”

Quantification and optimisation of lung ventilation SPECT images

“…Ventilation examinations using PET can be performed using for example inhaled Galligas (carbon nanoparticles connected to Gallium-68) (Ament et al, 2013;Hofman et al, 2011). Advantage with PET compared to SPECT is a higher spatial resolution, full tomographic acquisition 360° around the subject with potentially better regional quantification (Hofman et al, 2011).…”