CT Perfusion Imaging Captures Anatomy, Function

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Computed tomographic perfusion (CTP) imaging with a 128-dual source scanner offers good diagnostic accuracy at low radiation exposure compared with conventional imaging methods. The results, from a preliminary clinical study, were published online August 23, 2011, ahead of print in Circulation: Cardiovascular Imaging.

Researchers led by Gudrun M. Feuchtner, MD, of Innsbruck Medical University (Innsbruck, Austria), evaluated the method in 39 patients at intermediate-to-high risk of CAD. All underwent adenosine-induced stress 128-slice myocardial CTP imaging (Somatom Definition Flash; Siemens Healthcare, Forchheim, Germany). Its diagnostic accuracy was compared with that of invasive angiography (n = 25) and adenosine stress cardiac magnetic resonance (CMR) imaging (n = 30) in the same patient cohort.

CTP Provides Information at Stress, Rest

The 2-step CTP protocol involved:

• Adenosine stress CTP using a high-pitch factor (3.4) ECG-synchronized spiral mode
• Rest CTP/coronary computed tomographic angiography (CTA) using either high-pitch or prospective ECG-triggering depending on whether patient heart rate was below or above 65 bpm

Overall, the CTP protocol resulted in a total effective radiation dose of 2.5 ± 2.1 mSv. Mean heart rate was 69 bpm during stress CTP and 58 during rest CTP.

Compared with CMR, stress CTP was able to detect both myocardial perfusion defects and reversible ischemia (table 1).

Table 1. Diagnostic Accuracy of Stress CTP vs. CMR: Per Segment (n = 480)

Abbreviations: PPV, positive predictive value; NPV, negative predictive value.

Compared with invasive angiography, the combination of CTP and CTA was able to detect greater than 70% stenosis (table 2).

Table 2. Diagnostic Accuracy of CTP/CTA: Per Vessel (n = 75)

Abbreviations: PPV, positive predictive value; NPV, negative predictive value.

In an e-mail communication, Dr. Feuchtner emphasized CTP’s ability to reduce radiation exposure. CTP can image the entire heart in less than 0.3 seconds, compared with the 6 seconds required for conventional CT scans. In addition, the new CT protocol is unique in that it images both coronary arteries and myocardial perfusion, he said.

A Welcome Addition

As to how this method would be used in clinical practice, Matthew J. Budoff, MD, of Harbor-UCLA Medical Center (Torrance, CA), told TCTMD in a telephone interview that CTP would supplement the information now being provided by CTA.

Ordinarily, “once you do a CTA, if you’re not clear what’s going on, you have to do a stress nuclear or a stress echo. This appears to have better results than [either of those tests]. They’re trying to create an ‘all-in-one shop,’” he explained.

By looking at both anatomy and function, CTP “holds a lot of promise as a protocol and will certainly add a lot more than our traditional function-only testing, which I think is somewhat outdated at this point,” Dr. Budoff noted. He added that stress testing alone might not identify patients who “could have a whole bunch of blockages that do not yet need stenting but need cholesterol medication, lifestyle changes, aspirin, and other therapies.”

In a telephone interview with TCTMD, Michael Poon, MD, of Stony Brook University Medical Center (Stony Brook, NY), agreed, noting that CTP “adds a whole new dimension to CT.”

All 3 physicians said the test was best suited to patients who are at higher risk of CAD. “[They’re] not going to be the low-hanging fruit, so to speak,” Dr. Poon said, while Dr. Budoff acknowledged that patient selection “is going to be the hardest part right now. As with any new test, you want to make sure you’re applying it to the right population.”

Dr. Feuchtner suggested several patient subgroups likely to benefit most from CTP imaging:

• Those with an intermediate 50% to 70% stenosis found on CTA
• Those slated to undergo CABG or complex revascularization, such as PCI for chronic total occlusion
• Those with a high calcium score
• Diabetic patients without angina symptoms due to neuropathy

Easy to Use

Drs. Poon and Budoff both have firsthand experience with CTP imaging. Dr. Budoff, for example, is participating in a multicenter trial evaluating the method. “We’ve done a couple of [the tests] at our site already. It’s not technically that challenging to acquire these images, so I don’t think it’s going to require exceptional expertise on top of traditional CT training,” he reported.

Dr. Feuchtner agreed that the test would require no additional technical skills. “Still, there are some new things to learn (eg, artifacts on CT and related pitfalls),” he said. “I would suggest that radiologists and clinicians sit down together for an optimal learning curve.”

In fact, Dr. Poon pointed out that the CTP protocol does not even require new equipment. He and his colleagues have already been trying the method at Stony Brook. “It just happens they used a machine that was 128-slice; it can be 64 or 320. It doesn’t matter what scanner they used,” he stressed. “There’s nothing unique about this high-pitch 128-slice dual source CT scanner.”

Dr. Budoff noted that based on excitement over the new method, “[y]ou’re going to see a lot more in [the literature on CTP], both doing it with this new equipment and doing it with traditional 64-slice scanners. I think perfusion imaging is going to grow fairly rapidly, and hopefully save money by not requiring [patients to undergo] another test like a stress echo or stress nuclear.”

According to Dr. Poon, “this is another step toward using CT in a more diversified area, so that it’s not only limited to ruling out disease but also used to identify culprit lesions.”

Study Details

CMR was performed with a 1.5 Tesla unit (Phillips Achieva; Best, The Netherlands).

 

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Source:
Feuchtner G, Goetti R, Plass A, et al. Adenosine stress high-pitch 128-slice dual source myocardial computed tomography perfusion for imaging of reversible myocardial ischemia: Comparison with magnetic resonance imaging. Circ Cardiovasc Imaging. 2011;Epub ahead of print.

 

 

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