V/Q scintigraphy: alive, well and equal to the challenge of CT angiography

Abstract

It has been almost two decades since the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study was published [1], yet its conclusions remain controversial [2, 3]. Miscalculations in the design of the study, including the prospective parameters, can be attributed to the relatively limited fund of knowledge available to the creators of the PIOPED investigation. Within 3 years, modified criteria were retrospectively developed that, when applied to the PIOPED populations, provided more accurate results [4]. The enormous information that we have gained through the multiple retrospective analyses of the PIOPED data [5–10] are less well recognized than the original publication, although they have led to improvements in both the performance and the interpretation of V/Q scintigraphy. After 20 years, it is time to stop critiquing this invaluable study and move ahead with the greater knowledge and more sophisticated approach that we have developed toward V/Q scintigraphy. One of the major PIOPED critiques deals with the large number (44%) of intermediate/indeterminate interpretations. We believe this is related to the fact that 68% of the study population comprised inpatients who are more likely to have underlying cardiopulmonary disease, such as pneumonia, chronic obstructive lung disease and pleural effusions that will cause “triple matches”, resulting in intermediate or indeterminate interpretations. At Montefiore Medical Center, the great majority of our V/Q studies are performed in relatively young emergency department patients (average age in 2007 was 50.8 years, compared to 56.7 years for CT angiography) without these underlying conditions. We generally screen patients with chest radiography which, when normal or near-normal, can be followed with a very interpretable V/Q study. This was one of the important observations made from retrospective PIOPED analysis and described by the investigators and others [8, 11]. Our number of indeterminate interpretations in more than 2000 studies performed in 2006 and 2007 was 6.5%. Additionally, correlating the indeterminate studies with clinical findings and pretest probability often allows us to skew the interpretation to the low or high portion of the intermediate category making it clinically more useful. Shortly following the original PIOPED study, helical computed tomographic angiography (CTA) was introduced [12]. As additional refinements, including multirow detectors, were developed, CTA overtook V/Q scintigraphy as the most commonly performed imaging modality for suspected pulmonary embolism (PE) [13]. This advanced technology has allowed greater detection of subsegmental PE [14]. Interestingly and importantly, the benefit of diagnosing more PE is uncertain as the risk of recurrent thromboembolism and deaths have not declined [15]. An advantage of CTA is its ability to make alternative diagnoses, e.g., aortic dissection or pneumonia that may explain the patient’s symptoms [14, 16]. Magnetic resonance angiography (MRA) has been studied for nearly two decades, but has not yet found a routine role in the imaging of patients with suspected PE. Eur J Nucl Med Mol Imaging (2009) 36:499–504 DOI 10.1007/s00259-009-1068-2