Evaluation of Myocardial Perfusion by Computed Tomography - Principles, Technical Background and Recommendations.

Coronary computed tomography angiography (CCTA) has gained a prominent role in the evaluation of coronary artery disease. However, its anatomical nature does not allow the evaluation of the functional repercussion of coronary obstructions. It has been made possible to evaluate Myocardial computed tomography perfusion (Myocardial CTP) recently, based on myocardial contrast changes related to coronary stenoses. Several studies have validated this technique against the anatomical reference method (cardiac catheterization) and other functional methods, including myocardial perfusion scintigraphy and fractional flow reserve. The Myocardial CTP is performed in conjunction with the CCTA, a combined analysis of anatomy and function. The stress phase (with assessment of myocardial perfusion) can be performed before or after the resting phase (assessment of resting perfusion and coronary arteries), and different acquisition parameters are proposed according to the protocol and type of equipment used. Stressors used are based on coronary vasodilation (e.g. dipyridamole, adenosine). Image interpretation, similar to other perfusion assessment methods, is based on the identification and quantification of myocardial perfusion defects. The integration of both perfusion and anatomical findings is fundamental for the examination interpretation algorithm, allowing to define if the stenoses identified are hemodynamically significant and may be related to myocardial ischemia.

Evaluation of Myocardial Perfusion by Computed Tomography - Principles, Technical Background and Recommendations / Avaliação da Perfusão Miocárdica por Tomografia Computadorizada - Princípios, Fundamentação Técnica e Recomendações

Abstract Coronary computed tomography angiography (CCTA) has gained a prominent role in the evaluation of coronary artery disease. However, its anatomical nature does not allow the evaluation of the functional repercussion of coronary obstructions. It has been made possible to evaluate Myocardial computed tomography perfusion (Myocardial CTP) recently, based on myocardial contrast changes related to coronary stenoses. Several studies have validated this technique against the anatomical reference method (cardiac catheterization) and other functional methods, including myocardial perfusion scintigraphy and fractional flow reserve. The Myocardial CTP is performed in conjunction with the CCTA, a combined analysis of anatomy and function. The stress phase (with assessment of myocardial perfusion) can be performed before or after the resting phase (assessment of resting perfusion and coronary arteries), and different acquisition parameters are proposed according to the protocol and type of equipment used. Stressors used are based on coronary vasodilation (e.g. dipyridamole, adenosine). Image interpretation, similar to other perfusion assessment methods, is based on the identification and quantification of myocardial perfusion defects. The integration of both perfusion and anatomical findings is fundamental for the examination interpretation algorithm, allowing to define if the stenoses identified are hemodynamically significant and may be related to myocardial ischemia.

Resumo A angiografia coronariana por tomografia computadorizada (ACTC) assumiu um papel de destaque na avaliação da doença arterial coronariana. Entretanto, sua natureza anatômica não permitia a avaliação da repercussão funcional das obstruções coronarianas. Recentemente, tornou-se possível a avaliação da perfusão miocárdica por tomografia computadorizada (PMTC), baseando-se nas alterações de contrastação miocárdicas relacionadas às estenoses coronarianas. Diversos estudos permitiram validar esta técnica perante o método anatômico de referência (cateterismo cardíaco) e outros métodos funcionais, incluindo cintilografia de perfusão miocárdica e a reserva de fluxo fracionada. A PMTC é realizada conjuntamente com a ACTC, em uma análise combinada de anatomia e função. A fase de estresse (com avaliação da perfusão miocárdica) pode ser realizada antes ou depois da fase de repouso (avaliação da perfusão de repouso e artérias coronárias), e diferentes parâmetros de aquisição são propostos conforme o protocolo e o tipo de equipamento utilizados. Os agentes estressores utilizados baseiam-se na vasodilatação coronariana (ex: dipiridamol, adenosina). A interpretação das imagens, semelhante a outros métodos de avaliação perfusional, baseia-se na identificação e quantificação de defeitos de perfusão miocárdicos. A integração dos achados perfusionais e anatômicos é parte fundamental do algoritmo de interpretação do exame, permitindo definir se as estenoses identificadas são hemodinamicamente significativas, podendo se relacionar com isquemia miocárdica.

Cohort study of cardiovascular risk in asymptomatic young adults: subclinical atherosclerosis and coronary calcium score.

Coronary artery calcification is an early marker of subclinical atherosclerosis, but little research has been done in asymptomatic individuals under 45 years. In this cohort study with 17 years of follow-up, 155 participants were assessed in 2016 with a coronary calcium score for the association with cardiovascular risk factors. During follow-up, there was a significant increase in anthropometric measurements, cholesterol and fractions, and diastolic pressure. Participants who gained 1 cm in waist circumference had a mean reduction of 0.36 mg/dL in HDL-cholesterol and those who gained 1 kg/m2 in body mass index had a reduction of 0.72 mg/dL in HDL-cholesterol. Married participants had a 4.78 mg/dL reduction in HDL-cholesterol levels compared to singles. There was an increase of 2.09 mg/dL in HDL-cholesterol at each higher level of self-perceived health. One single case, a 32-year-old male, smoker, sedentary individual with a family history of cardiovascular disease, presented coronary calcification (0.6%). His HDL-cholesterol was reduced by 43.4%, with levels of less than 25 mg/dL at the time of coronary calcium scoring. Our findings may prompt broader studies of populations under 35 years with HDL-C levels below 25 mg/dL and family histories of cardiovascular disease, associated with obesity, sedentary lifestyle and smoking.

Prognostic value of routine cardiac magnetic resonance assessment of left ventricular ejection fraction and myocardial damage: an international, multicenter study.

BACKGROUND: Cardiac magnetic resonance (CMR) is considered the reference standard for assessment of left ventricular ejection fraction (LVEF) and myocardial damage. However, few studies have evaluated the relationship between CMR findings and patient outcome, and of these, most are small and none multicenter. We performed an international, multicenter study to assess the prognostic importance of routine CMR in patients with known or suspected heart disease. METHODS AND RESULTS: From 10 centers in 6 countries, consecutive patients undergoing routine CMR assessment of LVEF and myocardial damage by cine and delayed-enhancement imaging (DE-CMR), respectively, were screened for enrollment. Clinical data, CMR protocol information, and findings were collected at all sites and submitted to the data coordinating center for verification of completeness and analysis. The primary end point was all-cause mortality. A total of 1560 patients (age, 59±14 years; 70% men) were enrolled. Mean LVEF was 45±18%, and 1049 (67%) patients had hyperenhanced tissue (HE) on DE-CMR indicative of damage. During a median follow-up time of 2.4 years (interquartile range, 1.2, 2.9 years), 176 (11.3%) patients died. Patients who died were more likely to be older (P<0.0001), have coronary disease (P=0.004), have lower LVEF (P<0.0001), and have more segments with HE (P<0.0001). In multivariable analysis, age, LVEF, and number of segments with HE were independent predictors of mortality. Among patients with near-normal LVEF (≥50%), those with above-median HE (>4 segments) had reduced survival compared to patients with below- or at-median HE (P=0.02). CONCLUSIONS: Both LVEF and amount of myocardial damage as assessed by routine CMR are independent predictors of all-cause mortality. Even in patients with near-normal LVEF, significant damage identifies a cohort with a high risk for early mortality.

Extent of myocardial scarring on nonstress delayed-contrast-enhancement cardiac magnetic resonance imaging correlates directly with degrees of resting regional dysfunction in chronic ischemic heart disease.

BACKGROUND: Hyper-enhancement on delayed-enhancement magnetic resonance imaging (DE-MRI) is a marker of irreversible myocardial injury. Both reversible and irreversible ischemically injured regions of myocardium develop reductions in systolic function compared with unaffected regions. This study evaluated whether there is a relationship between myocardial hyper-enhancement from remote scarring on DE-MRI and the degree of myocardial circumferential shortening (%CS) as determined with dynamic MRI tissue tagging (TAG-MRI) in the setting of chronic ischemic heart disease (CIHD). METHODS: Thirty-five patients with CIHD and 8 control patients underwent nonstress, resting DE-MRI and TAG-MRI. A total of 168 CIHD and 96 control segments from the basal- and middle-thirds of the left ventricle (LV) were selected to achieve a balanced test set. With a 16-segment model, segmental myocardial scarring was graded on the basis of the amount of hyper-enhancement on DE-MRI. With TAG-MRI images, segmental %CS was calculated. RESULTS: Patients with CIHD had lower LV ejection fraction compared with the control patients (28% vs 67%). The %CS of normal segments was notably different from %CS of CIHD segments, regardless of the presence or absence of myocardial hyper-enhancement on DE-MRI. Among the CIHD segments, however, %CS correlated inversely with the amount of myocardial hyper-enhancement from scarring (P <.0001, r = -0.38). CONCLUSIONS: On cardiac MRI for CIHD, myocardial hyper-enhancement correlates inversely with %CS, supporting the direct relationship between the amount of remote myocardial scarring determined with nonstress DE-MRI and baseline resting functional impairment.

Nonstress delayed-enhancement magnetic resonance imaging of the myocardium predicts improvement of function after revascularization for chronic ischemic heart disease with left ventricular dysfunction.

BACKGROUND: The extent of myocardial scarring of the left ventricle (LV) is important in patients with chronic ischemic heart disease (CIHD). With delayed-enhancement magnetic resonance imaging (DE-MRI), scarred myocardium (hyper-enhanced) is easily distinguishable from viable (dark) myocardium. This investigation assessed the use of DE-MRI for predicting functional improvement after coronary artery bypass grafting (CABG) in patients with CIHD and significant LV dysfunction. METHODS: The patient population (n = 29) with CIHD and LV dysfunction (ejection fraction 28% +/- 10%) underwent both DE-MRI, to delineate scarred regions before revascularization, and echocardiography (Echo), to assess segmental function before and after CABG (interval 188 +/- 57 days). Using a 16-segment model, LV myocardium was semiquantitatively analyzed for scarring based on DE-MRI and for improvements in resting function by pre- and post-CABG Echo. RESULTS: Before CABG, 82% of targeted myocardial segments had abnormal contraction; 78% showed scarring, including 38% with greater than mild amounts (25%-100%). Normal contraction was found in 18% of segments before revascularization; scarred areas were identified in 42%, 84% of which had, at most, minimal amounts (0%-24%). Of segments with pre-CABG dysfunction, 82% with no evidence of scar recovered, compared to only 18% with > or =50% scarring. Amount of hyper-enhancement was a very good indicator of improvement of function, especially at the > or =50%/segment threshold; overall accuracy was 0.74 (95% CI 0.66-0.82, P <.001). CONCLUSIONS: In patients with CIHD and significant LV dysfunction, DE-MRI can predict likelihood of functional improvement after revascularization.

Three-dimensional reconstruction of pulmonary veins in patients with atrial fibrillation and controls: morphological characteristics of different veins.

Multidetector computed tomography can be used to evaluate the anatomy of pulmonary veins (PVs) in patients with AF. The study evaluated two groups. Group 1 included 61 patients assessed following PV ablation with ultrasound of RF energy. Group 2 included 15 patients undergoing ablation for AF and 14 control subjects without a history of AF matched for age and sex. The anatomy of the PVs was analyzed in this group prior to the ablation and compared to controls. Computed tomography was used to measure the ostium of the left superior, left inferior, right superior, right inferior PVs, and the left atrial appendage size. In group 1, PV stenosis was seen in 14 (30%) of 46 patients undergoing ablation with RF energy and in none of the 15 patients receiving ablation with ultrasound energy. In group 2, the ostium size was not different between patients with AF and controls. Similarly, the ostium of the PV that appeared to trigger AF was not larger than the ostium of the remaining veins. A "clustering pattern" of PV branches near the right inferior PV ostium was seen in almost every patient, independent of the presence of the arrhythmia. Computed tomography frequently detects PV stenosis following RF ablation. Ultrasound ablation does not appear to result in PV narrowing. Overall, patients with AF do not have larger sizes of PV ostia. Multiple ramifications from the right inferior PV ostium is a common pattern and may represent a protective anatomic variant.

Evaluation of left ventricular dysfunction using multiphasic reconstructions of coronary multi-slice computed tomography data in patients with chronic ischemic heart disease: validation against cine magnetic resonance imaging.

PURPOSE: Multi-slice computed tomography (MSCT) is an emerging technique for the angiographic assessment of coronary artery disease (CAD). The purpose of this work was to determine if multiphasic reconstructions of the same data used for the assessment of CAD could also be used for global functional evaluation of the left ventricle (LV). MATERIALS AND METHODS: Fifteen patients with chronic ischemic heart disease (CIHD) were imaged for CAD using a contrast-enhanced retrospective electrocardiographic-gated spiral technique on a MSCT scanner. The same data were reconstructed at both end-diastole and end-systole in order to measure left ventricular end-diastolic volume (LVEDV), end-systolic volume (LVESV), and ejection fraction (LVEF). The results were compared to values obtained using a cine true-fast imaging with steady-state precession technique on a magnetic resonance imaging (MRI) scanner. Interobserver variability in the measurement from MSCT images was also evaluated. RESULTS: For LVEF, there was substantial agreement between MSCT and MRI (intraclass correlation coefficient of 0.825); the intermodality reproducibility for LVEF (5%) was within an acceptable clinical range. However, mean values of LVEDV and LVESV with MSCT compared to cine MRI (LVEDV: 262.0 +/- 85.6 ml and 297.2 +/- 98.8 ml, LVESV: 196.2 +/- 75.6 ml and 218.6 +/- 90.99 ml, respectively) were significantly less for both volumes (p < 0.015). Intermodality variabilities for these measurements were high (15 and 13% for LVEDV and LVESV, respectively). Readers' mean measurements of LVESV from MSCT images were significantly different (p = 0.003) resulting in differences in calculation of LVEF (p < 0.024). Still, interobserver variabilities for all values were acceptable (6, 8, and 5% for LVEDV, LVESV, and LVEF, respectively). CONCLUSION: Although values for LVEDV and LVESV were less with MSCT than with MRI, LVEF values were in agreement. This suggests that combined imaging of CAD and the evaluation of global LV dysfunction due to CIHD is feasible with the same MSCT acquisition.

Clinical blood flow quantification with segmented k-space magnetic resonance phase velocity mapping.

PURPOSE: To evaluate the accuracy of segmented k-space magnetic resonance phase velocity mapping (PVM) in quantifying aortic blood flow from through-plane velocity measurements. MATERIALS AND METHODS: Two segmented PVM schemes were evaluated, one with seven lines per segment (seg-7) and one with nine lines per segment (seg-9), in twenty patients with cardiovascular disease. A non-segmented (non-seg) PVM acquisition was also performed to provide the reference data. RESULTS: There was agreement between the aortic flow curves acquired with segmented and non-segmented PVM. The calculated systolic and total flow volume per cycle from the seg-7 and the seg-9 scans correlated and agreed with the flow volumes from the non-seg scans (differences < 5%). Sign tests showed that there were no statistically significant differences (P-values > 0.05) between the segmented and the non-segmented PVM measurements [corrected]. Seg-9, which was the fastest among the three sequences, provided adequate spatial and temporal resolution (> 10 phases per cycle). CONCLUSION: Segmented k-space PVM shows great clinical potential in blood flow quantification.

Takayasu arteritis: utility and limitations of magnetic resonance imaging in diagnosis and treatment.

OBJECTIVE: Previous studies have confirmed the poor correlation of symptoms, signs, and levels of acute-phase reactants with disease activity in approximately 50% of all patients with Takayasu arteritis (TA). Invasive angiographic studies demonstrate vessel lumen anatomy, but do not provide qualitative information about the vessel wall. Moreover, sequential invasive angiographic studies expose patients to high-dose ionizing radiation and catheter/procedure-related morbidity. The aim of the present study was to determine the utility of new developments in vascular magnetic resonance (MR) technology in patients with TA. METHODS: Electrocardiogram-gated "edema-weighted" MR was used to evaluate the aorta and its primary branches with regard to the vascular lumen, vessel wall anatomy, and vessel wall edema in 24 TA patients (77 studies). Inclusion criteria were age <50 years and features of TA on both clinical examination and invasive angiographic studies. Patients were stratified based on clinical and laboratory indications of having either unequivocally active disease, inactive disease, or uncertain disease status. RESULTS: MR revealed vessel wall edema in 94% (17 of 18), 81% (13 of 16), and 56% (24 of 43) of studies obtained during periods of unequivocally active disease, uncertain disease activity, and apparent clinical remission, respectively. Westergren erythrocyte sedimentation rate and C-reactive protein values did not correlate with either the clinical assessment of disease activity or MR evidence of vascular edema. The frequency of presumed vascular inflammation (edema), as assessed by MR, in patients who appeared to be in remission was similar to the reported frequency of new angiographic lesions and histopathologic evidence of active disease in surgical specimens from patients thought to be in remission. However, the presence of edema within vessel walls did not consistently correlate with the occurrence of new anatomic changes found on subsequent studies. CONCLUSION: Inconsistencies in the presence or absence of vessel edema and subsequent anatomic changes have cast doubt on the utility of edema-weighted MR imaging as a sole guide to disease activity and treatment in TA. In this study, the greatest utility of MR was in providing a safe, noninvasive means of assessing changes in vascular anatomy.

Ultrafast flow quantification with segmented k-space magnetic resonance phase velocity mapping.

Magnetic resonance (MR) phase-velocity mapping (PVM) is routinely being used clinically to measure blood flow velocity. Conventional nonsegmented PVM is accurate but relatively slow (3-5 min per measurement). Ultrafast k-space segmented PVM offers much shorter acquisitions (on the order of seconds instead of minutes). The aim of this study was to evaluate the accuracy of segmented PVM in quantifying flow from through-plane velocity measurements. Experiments were performed using four straight tubes (inner diameter of 5.6-26.2 mm), under a variety of steady (1.7-200 ml/s) and pulsatile (6-90 ml/cycle) flow conditions. Two different segmented PVM schemes were tested, one with five k-space lines per segment and one with nine lines per segment. Results showed that both segmented sequences provided very accurate flow quantification (errors<5%) under both steady and pulsatile flow conditions, even under turbulent flow conditions. This agreement was confirmed via regression analysis. Further statistical analysis comparing the flow data from the segmented PVM techniques with (i) the data from the nonsegmented technique and (ii) the true flow values showed no significant difference (all p values>>0.05). Preliminary flow measurements in the ascending aorta of two human subjects using the nonsegmented sequence and the segmented sequence with nine lines per segment showed very close agreement. The results of this study suggest that ultrafast PVM has great potential to measure blood velocity and quantify blood flow clinically.