Planar Ventilation-Perfusion Imaging for Pulmonary Embolism: The Case for “Outcomes” Medicine
Section snippets
Overuse of Both V/Q and Computed Tomographic Pulmonary Angiography (CTPA)
Emergency department (ED) physicians generally are the first clinicians to examine patients with signs or symptoms suggestive of PE. They are under great pressure to triage rapidly and decide whether to discharge or hospitalize patients. In cases of suspected PE, use of either V/Q (or increasingly so) CTPA represents an attractive triage method. Most patients presenting to the ED have minimal risk factors. However, even with a low subjective or objective clinical probability, ED physicians are
Evidence of Overdiagnosis of PE
The 2006 Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II report evaluated the role of CTPA as a diagnostic study for PE16 with the use of a composite reference standard, including the Wells score (Table 1)17 and additional imaging. CTPA did not perform well when its results were discordant with the clinical probability. The negative predictive value (NPV) of CTPA was 60% when the clinical probability of PE was high and the positive predictive value (PPV) of CTPA was 58%
Why V/Q Instead of CTPA?
There has been attention in both the medical literature and the lay press about the increase in population radiation exposure from medical imaging, with a large proportion related to CT.24, 25, 26, 27, 28, 29 Breast radiation in young women (who represent a very significant proportion of patients studied for suspected PE) is a concern with regard to chest CTPA, and the lung remains susceptible to carcinogenic effects of radiation into old age. In fact, when dose-reduction strategies are not
Improvement in Interpreting V/Q Studies
Proponents of SPECT certainly will point to cross-sectional imaging's greater capability of detecting smaller lesions. We agree with this argument but, once again, it deals with accuracy rather than outcome. With the aforementioned similar NPV for planar V/Q and CTPA, the case for the adequacy of planar imaging remains convincing. Although CTPA and SPECT V/Q derive from differing sources, both are tomographic imaging modalities, and it is logical to extrapolate the points about CTPA regarding
The Problems with the PIOPED Study
One important problem with the initial 1990 PIOPED study was that 68% of the subjects studied were inpatients. The patients had a much greater incidence of underlying cardiopulmonary disease (with associated chest radiographic abnormalities) than a similar-sized outpatient population. Chest radiograph abnormalities make interpretation of V/Q scans more difficult. In retrospect, the PIOPED population was a suboptimal group to be imaged with V/Q scanning. This flaw in the study design resulted in
The Good Thing About PIOPED
The computer database generated by the PIOPED study has been used to greatly enhance our understanding and interpretation of the V/Q study.35
A Safe, Simple, and Accurate Algorithm to Study Patients With Suspected PE
In late 2006, a joint decision was made between 3 hospital departments (Emergency Medicine, Nuclear Medicine, and Radiology) at Montefiore Medical Center to reduce the number of CTPAs being performed for suspected PE. The Nuclear Medicine service took the lead in holding educational sessions with the support of our chest radiologists and emergency department physicians. After drawing upon lessons learned from the 1990 PIOPED report, it was decided that chest radiography could serve as an
The Language of Lung Scan Interpretation
The language of lung scan interpretation has long been a source of confusion both among requesting clinicians and the interpreters. This confusion was nicely documented by Scotland's Dr Harry Gray almost 2 decades ago.50, 51 He conducted separate surveys for both physician groups. Biello's original formulation36 associated low-probability interpretations with a <10% likelihood of PE. PIOPED, unfortunately, expanded this to a <20% likelihood of PE. Gray's survey of clinicians showed an
Conclusion: Planar Imaging Is “Good Enough”
Current practical barriers to implementation of SPECT V/Q include the current lack of an optimal ventilatory agent in the United States. Secondarily to this, most U.S. nuclear medicine physicians and radiologists are unfamiliar with SPECT V/Q interpretation on a practical basis and U.S. technologists generally lack sufficient experience to perform such studies. This is obviously not the case with CTPA and is often much less so with traditional V/Q. If Technegas becomes available in the United
Acknowledgments
The authors would like to thank Louisa Olmo for her invaluable assistance in the preparation of this manuscript.
References (58)
- et al.
Transition from planar to SPECT V/Q scintigraphy: Rationale, practicalities, and challenges
Semin Nucl Med
(2010) - et al.
Suspected and incidental pulmonary embolism on multidetector-row CT: Analysis of technical and morphological factors influencing the diagnosis in a cross-sectional cancer centre patient cohort
Clin Radiol
(2006) - et al.
Increased diagnosis of pulmonary embolism without a corresponding decline in mortality during the CT era
Clin Radiol
(2008) - et al.
The current and continuing important role of ventilation-perfusion scintigraphy in evaluating patients with suspected pulmonary embolism
Semin Nucl Med
(2008) - et al.
Subsegmental pulmonary embolism diagnosed by computed tomography: Incidence and clinical implicationsA systematic review and meta-analysis of the management outcome studies
J Thromb Haemost
(2010) - et al.
Enhanced lung scan diagnosis of pulmonary embolism with the use of ancillary scintigraphic findings and clinical correlation
Semin Nucl Med
(2001) - et al.
Stratification of patients according to prior cardiopulmonary disease and probability assessment based on the number of mismatched segmental equivalent perfusion defectsApproaches to strengthen the diagnostic value of ventilation/perfusion lung scans in acute pulmonary embolism
Chest
(1993) - et al.
The addition of clinical assessment to stratification according to prior cardiopulmonary disease further optimizes the interpretation of ventilation/perfusion lung scans in pulmonary embolism
Chest
(1993) - et al.
A comparison of single-photon emission CT lung scintigraphy and CT pulmonary angiography for the diagnosis of pulmonary embolism
Chest
(2009) - et al.
SPECT V/Q imaging
Semin Nucl Med
(2010)
Technegas—A new ventilation agent for lung scanning
Nucl Med Commun
Technegas
Tomographic imaging in the diagnosis of pulmonary embolism: A comparison between V/Q lung scintigraphy in SPECT technique and multislice spiral CT
J Nucl Med
Generation of planar images from lung ventilation/perfusion SPECT
Ann Nucl Med
Imaging of pulmonary embolism: Too much of a good thing?
JAMA
Accuracy or outcome in suspected pulmonary embolism
N Engl J Med
Small pulmonary emboli: What do we know?
Radiology
Computed tomographic pulmonary angiography vs ventilation-perfusion lung scanning in patients with suspected pulmonary embolism: A randomized controlled trial
JAMA
Success of a safe and simple algorithm to reduce use of CT pulmonary angiography in the emergency department
AJR Am J Roentgenol
Pulmonary embolism at CT angiography: Implications for appropriateness, cost, and radiation exposure in 2003 patients
Radiology
Multidetector computed tomography for acute pulmonary embolism
N Engl J Med
Use of a clinical model for safe management of patients with suspected pulmonary embolism
Ann Intern Med
Value of the ventilation/perfusion scan in acute pulmonary embolismResults of the prospective investigation of pulmonary embolism diagnosis (PIOPED)
JAMA
No fooling around: Direct visualization of pulmonary embolism
Radiology
The clinical significance of pulmonary embolism: Uncertainties and implications for treatment—A debate
J Intern Med
Time trends in pulmonary embolism in the United States: Evidence of overdiagnosis
Arch Intern Med
Computed tomography—An increasing source of radiation exposure
N Engl J Med
White Paper: Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging
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