Ventilation-perfusion (V/Q) lung scintigraphy: a long journey to a renewed position of prominence in diagnosing pulmonary embolism

Abstract

The ventilation-perfusion (V/Q) lung scan has traveled a long, circuitous path since its introduction for the diagnosis of pulmonary embolism (PE) in the 1960s. Its initial credibility was damaged following the publication of the PI-OPED study in 1990 and the emergence of computed tomographic pulmonary angiography (CTPA) in the mid-1990s. A considerable number of advances in both methodology and image interpretation have helped to restore the credibility of V/Q. There has also been considerable concern over the large radiation burden associated with CTPA. The issue of overdiagnosis and overtreatment of small PEs has also received a lot of attention. Although CTPA diagnoses more of these smaller PEs than V/Q, follow-up ''outcomes'' data show that they do not require treatment. The false-negative rates for both procedures are approximately 1 % and not significantly different from one another. Finally, a change from traditional probability interpretations to a simpler and similarly accurate trinary system has made V/Q scintigraphy interpretations easier to understand for the referring clinician.

Imaging of Patients Suspected of Having Pulmonary Thrombo-Embolic Disease; The Value of Chest X-Ray Combined with Perfusion Scan

“…This is particularly important in the chest x-ray findings because in-patients are most likely to have cardiopulmonary problems, abnormal xray findings and increased indeterminate interpretation. This was the main flaw of the PIOPED study, where 68% of in-patients were utilized, resulting in a 44% of indeterminate diagnosis of PE 15 . In the modified PIOPED study, the number of in-patients was reduced to 11%, thus reducing the indeterminate results.…”

“…In a couple of studies to compare the modified PIOPED II and the PISAPED parameters, statistics showed that the sensitivity and specificity were not significantly different (84.9% and 92.7%, respectively, for modified PIOPED II and 80.5% and 96.6%, respectively, for PISAPED) 15,16 . Furthermore, Miniati et al (1996), in their study, suggested that using the PISAPED criteria reduces the percentage of patients with indeterminate findings that will require an additional test to arrive at a diagnosis of positive or negative study for PE 16 .…”

Clinicians’ interpretation of ventilation/perfusion (V/Q) lung scan reports: Where are we today?

“…The choice of investigation depends on several factors, including renal dysfunction, pregnancy, contrast allergy, radiation exposure, and the clinician’s preference. [2 , 3 , 5] An unambiguous conclusion on a V/Q scan report is essential for correct interpretation by clinicians and further patient treatment.…”

“…According to this system, a high probability of PE scan equates to >85% likelihood of PE. [5] A very low probability of PE scan translates to <10% likelihood of PE. [5] The likelihood of PE is reported as a linguistic probability (high, indeterminate, low or very low probability) and not numerical percentages.…”

“… [5] A very low probability of PE scan translates to <10% likelihood of PE. [5] The likelihood of PE is reported as a linguistic probability (high, indeterminate, low or very low probability) and not numerical percentages. [12] In the event of an abnormal chest radiograph, a V/Q single-photon emission computed tomography (SPECT) technique is used.…”