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We read with interest the review by Takach Lapner and Kearon on pulmonary embolism (PE)1, but were
disappointed to see that, with regard to ventilation/perfusion (V/Q) scanning, the paper does not reflect the
current standard of clinical care. Planar (two-dimensional) scans, as described in the paper, are being
replaced by (three-dimensional) single-photon emission computerized tomography (SPECT) scans, following
publication of guidelines by the relevant European2;3 and American4 specialist societies. V/Q SPECT allows
detection of subsegmental PE5 and clearer depiction of some segmental PE that cannot be visualised on
planar scans6. For the referring clinician, SPECT does away with probability-based reporting and simply
diagnoses or excludes PE, with very few (<5%) non-diagnostic scans. V/Q SPECT has been compared to
CTPA using at least 16 slice scanners in two small studies, both using a composite reference standard (all
available imaging, clinical data, follow-up):
study
Bajc7
Gutte8
patients
152
81
sensitivity
97%
97%
V/Q SPECT
specificity PPV
89%
85%
88%
82%
NPV
98%
98%
sensitivity
43%
68%
CTPA
specificity
73%
100%
PPV
50%
100%
NPV
68%
83%
These data show that the diagnostic performance of V/Q SPECT for diagnosing PE is at least as good as
that of CTPA. Instead, we believe that the choice of imaging test for suspected PE should be based on
contraindications to exposure to X-ray iv contrast medium, radiation dose and local availability of either test.
Thomas Grüning, Consultant in Nuclear Medicine
[email protected]
Brent E Drake, Consultant in Nuclear Medicine and Radiology
Derriford Hospital, Plymouth
Reference List
(1) Takach Lapner ST, Kearon C. Diagnosis and management of pulmonary embolism. BMJ 2013;
346:f757.
(2) Bajc M, Neilly JB, Miniati M, Schuemichen C, Meignan M, Jonson B. EANM guidelines for
ventilation/perfusion scintigraphy : Part 1. Pulmonary imaging with ventilation/perfusion single photon
emission tomography. Eur J Nucl Med Mol Imaging 2009; 36(8):1356-1370.
(3) Bajc M, Neilly JB, Miniati M, Schuemichen C, Meignan M, Jonson B. EANM guidelines for
ventilation/perfusion scintigraphy : Part 2. Algorithms and clinical considerations for diagnosis of
pulmonary emboli with V/P(SPECT) and MDCT. Eur J Nucl Med Mol Imaging 2009; 36(9):1528-1538.
(4) Parker JA, Coleman RE, Grady E, Royal HD, Siegel BA, Stabin MG et al. SNM Practice Guideline for
Lung Scintigraphy 4.0. J Nucl Med 2012; 40(1):57-65.
(5) Bajc M, Bitzen U, Olsson B, Perez dS, V, Palmer J, Jonson B. Lung ventilation/perfusion SPECT in the
artificially embolized pig. J Nucl Med 2002; 43(5):640-647.
(6) Morrell NW, Roberts CM, Jones BE, Nijran KS, Biggs T, Seed WA. The anatomy of radioisotope lung
scanning. J Nucl Med 1992; 33(5):676-683.
(7) Bajc M, Olsson B, Palmer J, Jonson B. Ventilation/Perfusion SPECT for diagnostics of pulmonary
embolism in clinical practice. J Intern Med 2008; 264(4):379-387.
(8) Gutte H, Mortensen J, Jensen CV, Johnbeck CB, von der RP, Petersen CL et al. Detection of
pulmonary embolism with combined ventilation-perfusion SPECT and low-dose CT: head-to-head
comparison with multidetector CT angiography. J Nucl Med 2009; 50(12):1987-1992.