ABC | Volume 113, Nº4, October 2019

Review Article Magalhães et al. Principles of MPCT Arq Bras Cardiol. 2019; 113(4):758-767 Table 2 – Contrast dose and flow by patient weight53 weight (Kg) First phase: 100% Contrast (ml) Second phase: 30% contrast and 70% Serum (ml) Third phase: 100% serum (ml) Flow (ml/s) < 60 44 20 50 4 60-70 54 20 50 4.5 71-100 54 20 50 5 > 100 64 20 50 5 Modified table from George et al. 53 peak pharmacological stress acquisition, 32x1.0 mm collimation, 100 mA and 100 Kv (preferred). Devices with latest hardware and state-of-the-art software can take advantage of available technological advances (e.g. prospective acquisition) and be based on a protocol with less radiation and the same diagnostic capability. After iodinated contrast infusion, imaging acquisition can be performed manually as soon as the contrast is visually detected in the left atrium. 2 – Volumetric acquisition scanners (eg 240-320 detectors, or high-pitch beat acquisition): The rest protocol will simultaneously acquire anatomical image (coronary angiography) and myocardial perfusion. The start and end of acquisition should be programmed based on previously acquired calcium score images, trying to minimize the radiation dose. Acquisition parameters used include 240-320 0.5 mm detectors with 100-120 kV voltage probe, gantry rotation from 0.280 to 0.375 seconds, with prospective ECG trigger. Intravenous contrast will be infused by pump injection in a biphasic or three-phase protocol: 100% contrast in the first phase, 30% contrast plus 70% saline in the second phase, and 100% saline in the third phase. The contrast dose will be adjusted according to the patient’s weight (see Table 2). 53 Contrast injection monitoring must be performed by rapid real-time acquisitions initiated 5 seconds after the start of infusion. An apnea command is to be performed 14 seconds after the start of intravenous contrast infusion. When the contrast density peak reaches 300 UH in the descending aorta, acquisition of resting myocardial perfusion images and coronary angiography by CT will be initiated. The pharmacological stress protocol will focus on stress myocardial perfusion image. Again, the beginning and end of the acquisition should be programmed based on previously acquired images, calcium score and rest perfusion. Acquisition parameters used include 240-320 0.5mmdetectors with 100‑120 kV tube voltage, gantry rotation from 0.280 to 0.375 seconds with a prospective ECG trigger. 53 Following administration of the stressor, a 12-lead ECG should be performed, along with blood pressure and heart rate checks. 3 – Other protocols Different techniques and forms of image acquisition are available and constantly evolving, including dual energy and dynamic acquisition. Although promising, such techniques require further investigation and radiation reduction strategies. Therefore, we will not address the protocols used for such techniques in this document. CCTA/CTMP Interpretation and Integration The assessment of CTMP involves a sequence of steps, which must be systematized to produce a result that reflects a physiopathological change or a state of normality. In this approach, initial assessment of CCTA is recommended (Figure 2), 57 given that the additional value of CT perfusion defects in the absence of atherosclerosis has not been investigated so far. Once the CCTA is evaluated and any coronary stenosis and non-interpretable segments (stents, calcifications, artifacts) are quantified, the next step is to assess stress and rest myocardial perfusion. At this stage, qualitative and quantitative visual analyses (below) are used to establish the severity and extent of myocardial perfusion deficit, as well as its reversibility. The third step in the process of image interpretation is the reclassification of anatomical findings. Due to potential limitations of luminal assessment by CCTA and the existence of intermediate stenoses, 22,51,58 myocardial perfusion analysis may be the information required to define obstruction. In this sense, in coronary segments whose evaluation was doubtful for any reason, the presence of myocardial ischemia observed by the Myocardial CTP should strongly suggest significant stenosis. The final step in the interpretation process is anatomical- perfusion alignment based on the integration of CCTA and Myocardial CTP findings. This process is essential to define the presence of flow-limiting stenoses, 24 i.e. the presence of epicardial obstructions causing myocardial perfusion defects, whether fixed (fibrosis) or reversible (ischemia). This correlation should be performed mainly by multiplanar reconstructions, in order to align each epicardial vessel with its respective myocardial territory, defined by well-established myocardial segmentation models. 59 This process should produce a correlation between epicardial stenoses and eventual perfusion defects, whose description should clear and detailed in the final report. Quantitative analysis of myocardial stress perfusion by tomography Among the methods used for quantitative evaluation we can mention transmural perfusion ratio (TPR) and summed stress score (SSS), obtained through static acquisition. MBF estimates, although likely to be performed by dynamic myocardial perfusion, will not be addressed in this document. 762