Aim. The aim of this retrospective study is to illustrate clinical utility and impact of pulmonary embolism (PE) diagnostics of up to date Ventilation ⁄ Perfusion SPECT (V ⁄ P SPECT ) applying holistic interpretation criteria.Material and methods. During a 2-year period 2328 consecutive patients referred to V ⁄ P SPECT for clinically suspected PE were examined. Final diagnosis was established by physicians clinically responsible for patient care. To establish the performance of V ⁄ P SPECT negative for PE, patients were followed up by medical records for 6 months.Results. Ventilation ⁄ Perfusion SPECT was feasible in 99% of the patients. Data for follow-up were available in 1785 patients (77%). PE was reported in 607 patients (34%). Normal pattern was described in 420 patients (25%). Pathology other than PE such as a pneumonia, left heart failure, obstructive lung disease, tumour was described in 724 patients (41%). Report was nondiagnostic in 19 patients (1%). Six cases were classified as falsely negative because PE was diagnosed at follow-up and was fatal in one case. Six cases were classified as falsely positive because the clinician decided not to treat. In 608 patients with final PE diagnosis, 601 patients had positive V ⁄ P SPECT (99%). In 1177 patients without final PE diagnosis 1153 patients had negative V ⁄ P SPECT (98%).Conclusions. Holistic interpretation of V ⁄ P SPECT, yields high negative and positive predictive values and only 1% of nondiagnostic findings and was feasible in 99% of patients. It is a responsibility and a challenge of nuclear medicine to provide optimal care of patients with suspected PE by making V ⁄ P SPECT available.

Pulmonary embolism (PE) can only be diagnosed with imaging techniques, which in practice is performed using ventilation/perfusion scintigraphy (V/P(SCAN)) or multidetector computed tomography of the pulmonary arteries (MDCT). The epidemiology, natural history, pathophysiology and clinical presentation of PE are briefly reviewed. The primary objective of Part 1 of the Task Group's report was to develop a methodological approach to and interpretation criteria for PE. The basic principle for the diagnosis of PE based upon V/P(SCAN) is to recognize lung segments or subsegments without perfusion but preserved ventilation, i.e. mismatch. Ventilation studies are in general performed after inhalation of Krypton or technetium-labelled aerosol of diethylene triamine pentaacetic acid (DTPA) or Technegas. Perfusion studies are performed after intravenous injection of macroaggregated human albumin. Radiation exposure using documented isotope doses is 1.2-2 mSv. Planar and tomographic techniques (V/P(PLANAR) and V/P(SPECT)) are analysed. V/P(SPECT) has higher sensitivity and specificity than V/P(PLANAR). The interpretation of either V/P(PLANAR) or V/P(SPECT) should follow holistic principles rather than obsolete probabilistic rules. PE should be reported when mismatch of more than one subsegment is found. For the diagnosis of chronic PE, V/P(SCAN) is of value. The additional diagnostic yield from V/P(SCAN) includes chronic obstructive lung disease (COPD), heart failure and pneumonia. Pitfalls in V/P(SCAN) interpretation are considered. V/P(SPECT) is strongly preferred to V/P(PLANAR) as the former permits the accurate diagnosis of PE even in the presence of comorbid diseases such as COPD and pneumonia. Technegas is preferred to DTPA in patients with COPD.

These guidelines update the previous EANM 2009 guidelines on the diagnosis of pulmonary embolism (PE). Relevant new aspects are related to (a) quantification of PE and other ventilation/perfusion defects; (b) follow-up of patients with PE; (c) chronic PE; and (d) description of additional pulmonary physiological changes leading to diagnoses of left ventricular heart failure (HF), chronic obstructive pulmonary disease (COPD) and pneumonia. The diagnosis of PE should be reported when a mismatch of one segment or two subsegments is found. For ventilation, Technegas or krypton gas is preferred over diethylene triamine pentaacetic acid (DTPA) in patients with COPD. Tomographic imaging with V/PSPECT has higher sensitivity and specificity for PE compared with planar imaging. Absence of contraindications makes V/PSPECT an essential method for the diagnosis of PE. When V/PSPECT is combined with a low-dose CT, the specificity of the test can be further improved, especially in patients with other lung diseases. Pitfalls in V/PSPECT interpretation are discussed. In conclusion, V/PSPECT is strongly recommended as it accurately establishes the diagnosis of PE even in the presence of diseases like COPD, HF and pneumonia and has no contraindications.

SummaryPlanar lung ventilation/perfusion scintigraphy (V/P PLANAR ) is a standard method for diagnosis of pulmonary embolism (PE). The goals of this study were to test whether the diagnostic information of ventilation/perfusion tomography (V/P SPET ) applied in clinical routine might enhance information compared with V/P PLANAR and to streamline data processing for the demands of clinical routine. This prospective study includes 53 patients suspected for PE referred for lung scintigraphy. After inhalation of 99m Tc-DTPA planar ventilation imaging was followed by tomography, using a dual-head gamma camera. 99m Tc-MAA was injected i.v. for perfusion tomography followed by planar imaging. Patients were examined in supine position, unchanged during V/P tomography. Two reviewers evaluated V/P PLANAR and V/P SPET images separately and randomly. Mismatch points were calculated on the basis of extension of perfusion defects with preserved ventilation. Patients were followed up clinically for at least 6 months. With V/P SPET the number of patients with PE was higher and 53% more mismatch points were found. In V/P SPET interobserver variation was less compared with V/P PLANAR . Ancillary findings were observed by both techniques in half of the patients but more precisely interpreted with V/P SPET . V/P SPET shows more and better delineated mismatch defects, improved quantification and less interobserver variation compared with V/P PLANAR . V/P SPET is amenable to implementation for clinical routine and suitable even when there is demand for a high patient throughput.

Lung scintigraphy is primarily used to diagnose pulmonary embolism. Ventilation imaging is often performed using 99m Tc-DTPA or Technegas, an ultrafine dispersion of 99m Tc-labeled carbon. Despite the common use of these radioaerosols, they have not been compared in an intraindividual study, and not with ventilation-perfusion (V/P) SPECT. The aim of the present head-tohead study was to systematically investigate differences in ventilation studies performed with 99m Tc-diethylenetriaminepentaacetate (DTPA) and Technegas. Methods: Sixty-three patients, 28 without and 35 with obstructive lung disease, were examined with V/P SPECT using both 99m Tc-DTPA and Technegas. V/P SPECT images were randomized and assessed independently by 2 masked physicians according to a predefined scoring system. A paired comparison was performed using the Wilcoxon signed-rank test. Results: In both obstructive and nonobstructive disease, the overall unevenness of radiotracer deposition and the degree of central deposition were more pronounced in 99m Tc-DTPA than Technegas studies. Because of better peripheral penetration, the extent of reverse mismatch was less when Technegas was used. Additionally, in obstructive disease, the degree of focal deposition in distal airways was more pronounced with 99m Tc-DTPA. Mismatched perfusion defects were more frequently found with Technegas in obstructive disease. Conclusion: This intraindividual comparative study shows that Technegas is the preferred radioaerosol, particularly in obstructive disease.Key Words: pulmonary embolism; ventilation-perfusion singlephoton emission computed tomography (V/P SPECT); COPD; 99m Tc-DTPA; Technegas Lung scintigraphy allows imaging of ventilation and perfusion distribution and assessment of regional lung function in lung disease (1). Lung scintigraphy is used primarily to identify pulmonary embolism (PE), although other diseases such as pneumonia, heart failure, and obstructive lung disease may be identified (1-5). Ventilationperfusion (V/P) SPECT improves the diagnostic accuracy for PE (6-9). V/P SPECT performed according to the state of the art also simplifies recognition of ventilation and perfusion patterns typical of other cardiopulmonary diseases (10).Perfusion scintigraphy is most commonly achieved by microembolization with 99m Tc-labeled macroaggregates of human albumin (MAA). For ventilation studies, the inert gas 81m Kr and the aerosols 99m Tc-diethylenetriaminepentaacetate (DTPA) and an ultrafine dispersion of 99m Tc-labeled carbon (Technegas; Cyclomedica Ltd.) are currently recommended (11). 81m Kr is of limited use because of its high cost and short half-life.Previously, 133 Xe was also used for ventilation studies, but this is no longer recommended according to the guidelines of the European Association of Nuclear Medicine (11).How aerosol droplets or particles are distributed and deposited within airways and alveoli depends on their aerodynamic properties, particularly their mass median aerodynamic diameter (11). Even with the best liquid aerosol gen...