**6. Conclusion and further perspective**

**5.1. Image acquisition and protocols**

204 Interventional Cardiology

Like other functional imaging methods, ordinary acquisition of CTMP consists of three sequences: a rest acquisition, an acquisition under pharmacological stress, and an acquisition of late enhancement. This approach is used to evaluate the reversibility of the ischemia [6].

Adenosine is used during the pharmacological stress acquisition for dilation of the coronary arteries with a dose ratio of 140 μg kg−1 min−1. This leads to a decrease of the perfusion pressure. However, compensatory dilatation of obstructed arteries is limited. Reversible ischemia is the result of decreased perfusion reserves within these vessels. This pathophysiological phenomenon is called the "steal-effect." After 2–3 min of continuous administration of adenosine with monitoring of ECG, pulse oximetry, and blood pressure, iodinated contrast agent is injected and image acquisition starts [6]. Beyond the application of iodinated contrast agent during rest and stress acquisition and adenosine during stress acquisition, beta blockers, and nitrates were administered immediately before the examination to avoid motion artifacts and to improve image quality [59]. Contraindication (e.g., contrast agent allergy, severe COPD, severe aortic valve stenosis) should be taken into consideration regarding suitability of the patient. After 5–10 min of administration of contrast agent, a delayed acquisition can provide information about nonviable myocardium [6]. Myocardial areas of ischemia or infarction are

Regarding comparability of studies and deeper understanding, it should be noted that there is a static myocardial blood pool imaging method during first pass and apart from it a dynamic myocardial perfusion method over several time points of myocardial iodine distribution. Development in computed tomography offers with dual-energy CT a further static perfusion method. For example, differences between these techniques apply on the direct assessment of

Radiation dose of a comprehensive protocol containing rest, stress, delayed enhancement, and calcium scoring have generally been reported in the range of 12–14 mSv. This is comparable to the radiation dose during SPECT examination [6]. Modified protocols in research contain considerably lower radiation. Feuchtner et al. achieved high accuracy (sensitivity 96%, specificity 88%, PPV 93%, and NPV 94%) in a stress approach and reported radiation dose of 2.5 mSv for cCTA and perfusion imaging with pharmacological stress [61]. Radiation doses for CTMP can be expected to decrease further, as radiation doses <1 mSv on cCTA studies are

As mentioned in the introduction of this chapter, CT myocardial perfusion offers additional functional data of the myocardial blood supply. In contrast, ordinary cCTA only provides anatomical evaluation of the heart. Combined cCTA plus CTMP provides incremental diagnostic value compared with cCTA alone to assess the status of the myocardial blood supply

described based on the American Heart Association segmental model [14].

quantitative perfusion parameters or radiation exposure [6, 60].

and for the detection of significant coronary stenosis [6, 57, 58].

**5.2. Radiation exposure**

still state of the art [61].

**5.3. Clinical setting**

Myocardial perfusion derived from computed tomography is a growing diagnostic method that provides a comprehensive evaluation of coronary artery disease along with functional assessment of the myocardium with promising findings in current clinical studies. Combining cCTA with CTMP significantly improves specificity and positive predictive value [57, 58].

The multicentre DECIDE-Gold trial [66] might contribute in establishment myocardial perfusion within the clinical setting. Focus of current research is, e.g., the order and general need of all three sequences in times of modern dual energy computed tomography scanners. Meinel et al. postulates a dual energy rest-stress approach as protocol of choice. Furthermore, he achieves excellent sensitivity and specificity in a rest-only approach [67]. This would represent substantial advantage for the patient. Functional situation of myocardial blood supply could be derived simultaneously from ordinary coronary computed tomography angiography within the same examination, without additional radiation, drugs or prolonged examination.

CT myocardial perfusion imaging offers great potential to reclassify findings in cCTA and to evaluate the myocardial blood supply [68]. Regarding risk of invasive coronary angiography [69], an initial noninvasive diagnostic selection would be desirable to reduce invasive angiograms, showing no obstructive CAD. Addition of CTMP to cCTA holds highly promising potential to adopt this role and to establish CT as a single imaging examination for comprehensive evaluation of CAD and direct assessment of myocardial ischemia in one examination (**Figure 1**).

**Figure 1.** 59-year-old female with known hypertension presenting with chest pain. (I) cCTA show several moderate stenoses of the LAD (arrows). **(II)** DECT show minor iodine distribution within basal LAD and RCA territory as a sign of hemodynamic significance (arrows). **(III)** Invasive catheter angiography show severe artery disease of all three vessels. Subtotal stenosis of RCA, significant stenosis of the left main trunk (arrow) and 75% stenosis of mid RCX and Ramus marginalis. cCTA, coronary computed tomography; DECT, dual-energy computed tomography; LAD, left anterior descending; RCA, right coronary artery; RCX, ramus circumflexus.

**Figure 2.(A)** cCTA shows stenotic noncalcified plaque of the LAD. **(B + C)** Color-coded automated plaque quantification by the analysis software showed the plaque composition as predominantly noncalcified. cCTA, coronary computed tomography angiography; LAD, left anterior descending.
