von Schulthess, Gustav

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European Journal of Nuclear Medicine and Molecular Imaging Vol. 31, No. 11, November 2004Eur J Nucl Med Mol Imaging (2004) 31:1462–1463DOI 10.1007/s00259-004-1685-8The article by Reinartz et al. raises interesting and im-portant issues regarding PET-CT by comparing PET andseparately acquired CT. The major conclusions of the authors are twofold. First, they conclude that only a rela-tively small number of patients would potentially benefitfrom PET-CT, given that the classification of a lesion re-mains equivocal in only a small number of patients whenPET and CT are carefully evaluated side-by-side. Sec-ond, they report that in almost half their patients, properinterpretation of a PET scan requires the availability of arecent CT scan for comparison. This fraction increases totwo-thirds if only those PET scans that show disease aretaken into account. This article is eye-opening with re-gard not only to the actual findings but also to the biasinduced by the vantage point from which the data areconsidered. PET-CT is a combined modality system. Theauthors view PET-CT from a nuclear medicine perspec-tive, but it may also be illustrative to consider PET-CTfrom a radiologist’s or, better still, a future integratedmodality imager’s perspective.From the vantage point of nuclear medicine, the really dramatic finding in this study is that almost half ofthe PET scans could not be properly interpreted alone,with CT also being required in order to properly classifythe findings. When only lesion-positive PET scans weretaken into account, this figure rose to 67%. It would beinteresting to ask what fraction of PET experts carefullyanalysed CT scans together with PET scans prior to thepre-PET-CT era. I freely admit that our team did not doso consistently before we started to operate our PET-CTscanner in early 2001. The data of Reinartz et al. amplydemonstrate that molecular and anatomical imagingmodalities are complementary, and that an intellectualsynthesis of the findings of the two modalities is ex-tremely relevant. Interpreting a PET scan without a cor-responding CT scan is apparently close to unacceptablemedical practice.From a nuclear medicine point of view, there are thussignificant advantages of PET-CT: 1. If it is indeed the case that half of all PET scans andtwo-thirds of positive PET scans need CT for properinterpretation, it would certainly be very convenientto acquire CT together with PET in a “one-stop shop”procedure. With this approach, the necessary data arealways available, and they are available in a formwhere electronic fusion of PET and CT images posesno major problems.2. In PET-CT, attenuation correction resulting in consis-tent lesion activity and allowing PET standardised uptake value measurements comes virtually free. Thehigher cost of the systems is offset by the higher pa-tient throughput.3. Fast transmission correction has the added advantagethat fluorodeoxyglucose (FDG) and other 18F-basedradiopharmaceuticals can be used more efficiently,thereby decreasing the per-dose cost of FDG.Thus, from a nuclear medicine perspective, PET-CT isadvantageous because it is practical, even though mostlesions can be classified when interpreting PET and CTside-by-side. CT, whether fused or separate, helps tospecify lesions: experience of the potential value of radi-ology in this respect was first gained 30 years ago whencomparing bone scans and X-rays of osseous and jointlesions. But, as then, the radiological part of the exami-nation offers much more than just a gain in specificity.From a radiologist’s perspective, things look differ-ent, and the article by Reinartz et al. does not discussthis. As clinicians become accustomed to PET-CT—andthey will quickly learn that PET without CT is less thanhalf as good—they will no longer order a CT scan andthen a separate PET scan, but will rather refer patientsdirectly to PET-CT instead. Then the issue will be opti-This Editorial Commentary refers to the articlehttp://dx.doi.org/10.1007/s00259-004-1593-y.Gustav K. von Schulthess (✉)University Hospital Zurich, Zurich, Switzerlande-mail: vonschulthess@dmr.usz.chEditorial commentaryMaximising the benefit of integrated PET/CT: the road aheadGustav K. von Schulthess11 University Hospital Zurich, Zurich, SwitzerlandPublished online: 5 October 2004© Springer-Verlag 2004future and want to keep PET-CT for themselves. Despitethis turf war, it is clear that competence in both fields isrequired, and few directors of nuclear medicine or radi-ology services are fortunate enough to be doubly boardcertified. The “turf problem” will become even more rel-evant with the introduction of more potent SPECT-CTsystems. However, while turf battles are currently beingfought over power or money, they will be irrelevant inthe future, because competence will prevail. This compe-tence is to be acquired, as always, through learning. Nu-clear physicians in training readily learn cross-sectionalimaging as they read PET-CT scans, and many young ra-diologists are now again opting to obtaining doubleboard certification. They understand that molecular im-aging is important and in essence resides with nuclearmedicine, because even the best method in this respect to be “owned” by the radiologists, namely magnetic resonance imaging, has major limitations with regard tomolecular imaging.So what is to be done in this situation? I believe thereis an urgent need for the imaging community to come together to define ways in which board-certified compe-tence in dual-modality imaging can be obtained. Ulti-mately the most reasonable approach will be the forma-tion of imaging departments which resemble neither radiology nor nuclear medicine departments but whichoffer board certification and subspecialisation titles inthe various, relatively disparate fields of imaging andimage-guided therapy. PET-CT may well be the imagingtechnology which allows both parties to stop feuding, totake a “fresh look at the battlefield” and to redraw“fences” in ways which make sense rather than beingbased on power and monetary issues only. I believe thatwe owe this to our young colleagues, who work hard inlearning the necessary prerequisites for success in medi-cal imaging. We should think less of defending our“turf” and more of defining reasonable prerequisites forboard certification so that our residents will become re-spected partners of our clinical colleagues. Both nuclearmedicine and radiology have developed so fast that thereis still plenty of ground to cover. Only through unity willwe be able to maintain the highest training standards,and this is the key to preventing clinicians from startingto perform these examinations by themselves. In oncolo-gy this may not be a major issue, but if a new generationof PET-CT or SPECT-CT scanners were able to providea “one-stop shop” examination for the heart, this couldbecome critical. Let us prepare now! A quote fromMikhail Gorbachev may be relevant in this context:“those who come late will be punished by life”.1463European Journal of Nuclear Medicine and Molecular Imaging Vol. 31, No. 11, November 2004misation not only of PET during PET-CT, but also of theCT component, so that all information relevant to a given diagnostic problem is obtained, thereby providinga true one-stop shop examination. How to perform theCT portion of the examination to provide an adequateone-stop shop in various diagnostic settings is a keyquestion that will require substantial clinical researchwork over the coming years. Some examinations may beadequate with unenhanced CT only, while other diagnos-tic situations will require the CT capabilities to theirmaximum. Thus, the trend in the industry to providePET-CT scanners with high- to medium-end CT scannersis understandable.What are the additional items of information that aCT scan offers over and above that provided by a PETscan? There is much relevant diagnostic informationwhich can be gained only with CT. In addition to the pre-cise lesion localisation afforded by CT in PET-CT, CTbut not PET is able to visualise disseminated small pul-monary metastases, pleural effusions and other fluid collections such as ascites or cystic structures, alterationsin lung and liver parenchyma, and calcifications, therebyfrequently offering additional relevant diagnostic infor-mation. With contrast enhancement, the relation of le-sions to vascular structures can be defined with CT; suchinformation may be of crucial relevance to the surgeonwhen operating on patients with central bronchial carci-noma or tumours affecting the upper abdomen andspecifically the liver. All this additional information, accessible using simple or more advanced CT imagingprotocols, may play a critical role in making the correctdiagnosis or providing accurate staging information. CTthus contributes sensitivity in addition to specificity.Reinartz et al. in essence ignore the CT information, asthey are using CT only to improve the classification ofthe PET lesions. They do not ask the question, “Whatcan CT itself add to PET-CT?”PET-CT has thus far been primarily in the hands ofnuclear physicians. Various solutions have been pro-posed to the question of how to gain the radiologicalcompetence needed to properly interpret the CT data.Frequently, nuclear physicians interpret the PET data andradiologists the CT data, and then discuss the case. Thismay be a reasonable start, particularly when substantialcross-training occurs, but it is certainly not cost effec-tive. It seems unfortunate that PET-CT is in danger ofbecoming the subject of a “turf war”: radiologists arewell aware of the power of PET and therefore want to“get a piece of the action”, while nuclear physicians realise that PET-CT is one or perhaps the avenue to their

Maximising the benefit of integrated PET/CT: the road ahead

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Maximising the benefit of integrated PET/CT: the road ahead

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