REPLY: It is surprising that Dr. Uren chose to write his letter to the editor of The Journal of Nuclear Medicine rather than to Seminars in Nuclear Medicine to express concern over articles appearing in the November 2008 issue of Seminars. We welcome the opportunity Dr. Schelbert has given us to respond to Dr. Uren's comments.
As the founding and ongoing editors of Seminars for the past 38 y, we have always striven to present a balanced picture of subject matter in the journal, particularly when controversy exists—as is the case regarding the relative roles of ventilation–perfusion (V/Q) scintigraphy and CT angiography in the diagnosis of pulmonary embolism. Four of the 7 articles in the November issue dealt with non-V/Q aspects of the pulmonary embolism debate. These 4 were the clinical overview and the discussions of lower-extremity ultrasound, CT angiography, and MRI (PIOPED III introduction). So the “collection of papers” referred to by Dr. Uren boils down to 3. One of the 3 specifically dealt with SPECT V/Q. The article by Freeman et al. (1) showed no illustrations and devoted a boldfaced paragraph to the virtues of SPECT. Perhaps Dr. Uren missed this, as he suggests that Dr. Roach's (2) was the only article that “mentioned” SPECT.
Dr. Uren's analogy between the use of 99mTc-exametazime (Ceretec; GE Healthcare) for brain studies and the use of V/Q for lung studies is misleading. From the first introduction of 99mTc-exametazime, brain imaging was, of necessity, a SPECT study. In such a case, SPECT is essential in order to visualize small intracerebral structures, which cannot be seen with planar imaging. This situation is definitely not comparable to that with V/Q imaging, in which choices exist. His argument might have been better served if he had stuck with the myocardial perfusion analogy. The article by Freeman et al. (1) mentions that the 1% false-negative rate in the Canadian study, as well as the 1.1% false-negative rate in our Montefiore study, supports the accuracy of the planar study. These 2 false-negative rates are quite similar to the results of the only published SPECT study with follow-up—a study that quoted a 98.5% negative predictive value (3). The rate of indeterminate interpretations in close to 2,000 planar V/Q studies performed at Montefiore during 2006 and 2007 was only 6.5%−7%, which we suspect is comparable to the rate in SPECT. Planar imaging has been quite successful in accomplishing our goal of significantly reducing the number of CT angiograms at our institution.
Dr. Uren should be aware that (Cyclopharma Corp. Technegas) is not available in the United States. It is universally agreed that this is the best ventilatory agent. In a recent editorial in Nuclear Medicine Communications, Roach et al. (4) pointed out that SPECT must be performed with a superior ventilation agent, for example, Technegas and a software display package that allows coregistered V/Q scans. Most American nuclear medicine physicians are not opposed to SPECT. We are just waiting for Technegas to receive Food and Drug Administration approval, which will, we hope, occur within the next year. We will likely be moving to SPECT at that point. It is also important to mention that although SPECT may seem logically superior to planar imaging for pulmonary embolism, the literature has insufficient evidence to support this conclusion. Conclusions that are not derived from evidence-based medicine are often incorrect.
We regret that Dr. Uren found our November issue of Seminars “quite depressing.” Perhaps another reading of the articles and a better understanding of why the unavailability of Technegas has inhibited SPECT V/Q growth in the United States would have allayed his concerns. Presently, planar V/Q imaging remains a valuable and reliable procedure in the diagnosis of pulmonary embolism.
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