Effect of image quality on myocardial extracellular volume quantification using cardiac computed tomography: a phantom study

Clinical Significance of Extracellular Volume of Myocardium (ECV) Assessed by Computed Tomography: A Systematic Review and Meta-Analysis

Background/Objectives: Extracellular volume (ECV) of the myocardium, a biomarker of interstitial space and fibrosis, plays a critical role in cardiac disease diagnosis and prognosis. Although cardiac magnetic resonance imaging (MRI) is the gold standard for ECV assessment, computed tomography (CT) offers a viable alternative, particularly in patients with contraindications to MRI. This study aimed to assess whether CT-derived ECV is systematically elevated in cardiac diseases associated with myocardial fibrosis. Methods: A systematic search of PubMed and Web of Science up to January 2023 identified 364 studies, including 16 from registers and 4 from manual searches. After exclusions, 73 studies were included in the systematic review. Of these, 15 provided quantitative data on group sizes, mean ECV values, standard deviations, and imaging modalities (CTA, DECT, LIE-DECT) and were analyzed in the meta-analysis. Standardized mean differences (SMD) were calculated using Cochrane Handbook formulas. Statistical analyses employed random-effects models (R version 4.4.2). Results: The pooled analysis showed that ECV was significantly higher in pathological groups compared to controls (SMD 1.60; 95% CI: 1.23-1.96; I2 = 84.6%). Elevated ECV correlated with worse clinical outcomes, including higher mortality in heart failure and advanced myocardial fibrosis in amyloidosis and cardiomyopathies. Subgroup analyses demonstrated that advanced CT techniques (DECT, LIE-DECT) and CTA provided comparable diagnostic accuracy. Conclusions: CT-derived ECV is a reliable, non-invasive marker of myocardial fibrosis, offering diagnostic and prognostic value similar to MRI. Standardizing CT protocols and conducting multicenter studies are essential to validate its broader clinical application.

Basic verification of myocardial extracellular volume quantification by prototype photon-counting detector computed tomography: A phantom study

Objectives

This study aimed to investigate the accuracy of myocardial extracellular volume (ECV) quantification using a prototype photon-counting detector (PCD) computed tomography (CT) and examine the association between radiation dose and spectral image settings.

Material and Methods

A multi-energy CT phantom that simulated the blood pool and myocardium was used. The tube voltage was set at 120 kVp and three types of tube current-time products (105, 150, and 300 mAs) were applied for pre- and post-contrast scans. Virtual monoenergetic images (VMIs) at 50-100 keV were reconstructed. The ECV value was calculated from the CT numbers between pre-contrast and post-contrast. We compared the accuracy of ECV values at each VMI level.

Results

Each radiation dose setting demonstrated a small but significant difference in ECV values at each keV level. ECV was overestimated at higher keV in all radiation dose settings. A significant difference in ECV value variabilities was found among keV levels in all three radiation dose settings, with higher keV exhibiting greater variability. The variation was particularly large in the low-dose setting. The residual values were significantly larger at higher keV levels in all radiation dose settings. The residual values were smaller at 50 and 60 keV with no significant difference in 150- and 300-mAs settings.

Conclusion

Setting appropriate VMI keV and radiation dose settings was necessary when quantifying myocardial ECV with PCD-CT because the keV levels caused differences in the quantification value and measurement variation.

Myocardial extracellular volume measurement using cardiac computed tomography

Myocardial fibrosis is a common endpoint of many cardiac diseases and increasingly recognized as a predictor of heart failure, arrhythmia, and death. Recent studies have utilised cardiac computed tomography (CT) scans with delayed phase imaging to quantify diffuse fibrosis of the myocardium. CT extracellular volume (CT-ECV) measurement correlates well with CMR and histological myocardial fibrosis. Furthermore, CT-ECV predicts outcomes such as death, heart failure and arrhythmia in various disease states. This review summarizes the rationale and methodology behind CT-ECV measurement and provides a detailed summary of the current clinical evidence for the use of CT-ECV.

Variation of computed tomography-derived extracellular volume fraction and the impact of protocol parameters: A systematic review and meta-analysis

BACKGROUND

Cardiac computed tomography quantification of extracellular volume fraction (CT-ECV) is an emerging biomarker of myocardial fibrosis which has demonstrated high reproducibility, diagnostic and prognostic utility. However, there has been wide variation in the CT-ECV protocol in the literature and useful disease cut-offs are yet to be established. The objectives of this meta-analysis were to describe mean CT-ECV estimates and to estimate the effect of CT-ECV protocol parameters on between-study variation.

METHODS

We conducted a meta-analysis of studies assessing CT-ECV in healthy and diseased participants. We used meta-analytic methods to pool estimates of CT-ECV and performed meta-regression to identify the contribution of protocol parameters to CT-ECV heterogeneity.

RESULTS

Thirteen studies had a total of 248 healthy participants who underwent CT-ECV assessment. Studies of healthy participants had high variation in CT-ECV protocol parameters. The pooled estimate of CT-ECV in healthy participants was 27.6% (95%CI 25.7%-29.4%) with significant heterogeneity (I2 ​= ​93%) compared to 50.2% (95%CI 46.2%-54.2%) in amyloidosis, 31.2% (28.5%-33.8%) in severe aortic stenosis and 36.9% (31.6%-42.3%) in non-ischaemic dilated cardiomyopathies. Meta-regression revealed that CT protocol parameters account for approximately 25% of the heterogeneity in CT-ECV estimates.

CONCLUSION

CT-ECV estimates for healthy individuals vary widely in the literature and there is significant overlap with estimates in cardiac disease. One quarter of this heterogeneity is explained by differences in CT-ECV protocol parameters. Standardization of CT-ECV protocols is necessary for widespread implementation of CT-ECV assessment for diagnosis and prognosis.

Diagnostic performance of unenhanced electrocardiogram-gated cardiac CT for detecting myocardial edema

To assess the diagnostic performance of unenhanced electrocardiogram (ECG)-gated cardiac computed tomography (CT) for detecting myocardial edema, using MRI T2 mapping as the reference standard. This retrospective study protocol was approved by our institutional review board, which waived the requirement for written informed consent. Between December 2017 to February 2019, consecutive patients who had undergone T2 mapping for myocardial tissue characterization were identified. We excluded patients who did not undergo unenhanced ECG-gated cardiac CT within 3 months from MRI T2 mapping or who had poor CT image quality. All patients underwent unenhanced ECG-gated cardiac CT with an axial scan using a third-generation, 320 × 0.5 mm detector-row CT unit. Two radiologists together drew regions of interest (ROIs) in the interventricular septum on the unenhanced ECG-gated cardiac CT images. Using T2 mapping as the reference standard, the diagnostic performance of unenhanced cardiac CT for detecting myocardial edema was evaluated by using the area under the receiver operating characteristic curve with sensitivity and specificity. Youden index was used to find an optimal sensitivity-specificity cutoff point. A cardiovascular radiologist independently performed the measurements, and interobserver reliability was assessed using intraclass correlation coefficients for CT value measurements. A P value of <.05 was considered statistically significant. We included 257 patients who had undergone MRI T2 mapping. Of the 257 patients, 35 patients underwent unenhanced ECG-gated cardiac CT. One patient was excluded from the study because of poor CT image quality. Finally, 34 patients (23 men; age 64.7 ± 14.6 years) comprised our study group. Using T2 mapping, we identified myocardial edema in 19 patients. Mean CT and T2 values for 34 patients were 46.3 ± 2.7 Hounsfield unit and 49.0 ± 4.9 ms, respectively. Mean CT values moderately correlated with mean T2 values (Rho = -0.41; P < .05). Mean CT values provided a sensitivity of 63.2% and a specificity of 93.3% for detecting myocardial edema, with a cutoff value of ≤45.0 Hounsfield unit (area under the receiver operating characteristic curve = 0.77; P < .01). Inter-observer reproducibility in measuring mean CT values was excellent (intraclass correlation coefficient = 0.93; [95% confidence interval: 0.86, 0.96]). Myocardial edema could be detected by CT value of myocardium in unenhanced ECG-gated cardiac CT.

Myocardial late enhancement and extracellular volume with single-energy, dual-energy, and photon-counting computed tomography

Computed tomography late enhancement (CT-LE) is emerging as a non-invasive technique for cardiac diagnosis with wider accessibility compared to MRI, despite its typically lower contrast-to-noise ratio. Optimizing CT-LE image quality necessitates a thorough methodology addressing contrast administration, timing, and radiation dose, alongside a robust understanding of extracellular volume (ECV) quantification methods. This review summarizes CT-LE protocols, clinical utility, and advances in ECV measurement through both single-energy and dual-energy CT. It also highlights photon-counting detector CT technology as an innovative means to potentially improve image quality and reduce radiation exposure.