Is a timely assessment of the hematocrit necessary for cardiovascular magnetic resonance-derived extracellular volume measurements?

Estimating synthetic hematocrit and extracellular volume from native blood pool T1 times at 3 Tesla CMR: Derivation of a conversion equation, accuracy and comparison with published formulas

PURPOSE

Calculation of extracellular volume fraction (ECV), a marker of myocardial fibrosis in cardiac magnetic resonance imaging (CMR), requires hematocrit (Hct). We aimed to correlate Hct levels with native blood T1 times, to derive a formula for estimating synthetic Hct (Hctsyn) and synthetic ECV (ECVsyn), to assess accuracy of ECVsyn and to compare our model with published formulas.

METHOD

In this retrospective study, a cohort of 250 CMR scans with T1 mapping (3T, MOLLI 5(3)3, endsystolic aquisition), was divided into a derivation and validation cohort. Native T1 times of the left ventricular blood pool (T1native,midLV) were correlated with Hct levels from blood sampling within 24 h (Hct24h) and a formula for calculation of Hctsyn was derived by linear regression.

RESULTS

In the derivation cohort (n = 167), Hct24h showed a good association with T1native,midLV (r = -0.711, p < 0.001). The resulting regression equation was Hctsyn = 1/T1native,midLV * 1355.52-0.310. In the validation cohort (n = 83), Hctsyn and Hct24h showed good correlation (r = 0.726, p < 0.001), while ECVsyn, and ECV24h demonstrated excellent correlation (r = 0.940, p < 0.001). ECVsyn had a minimal bias of 0.28 % and the misclassification rate (8.8 %) was comparable to the variability introduced by repeated Hct measurements (misclassification in 7.5 %). Applying published formulas in our cohort resulted in incorrect classification in up to 60 %.

CONCLUSION

We provide a formula for estimating Hctsyn from native blood T1 on a 3T scanner. The measurement error of ECVsyn is low and comparable to the error due to retest variability of conventional Hct. Scanner- and sequence-specific formulas should be used.

Hepatic and pancreatic extracellular volume fraction analysis using contrast-enhanced CT in patients with diabetes mellitus and pre-diabetes

PURPOSE

Liver and pancreatic fibrosis is associated with diabetes mellitus (DM), and liver fibrosis is associated with pancreatic fibrosis. This study aimed to investigate the relationship between the hepatic and pancreatic extracellular volume fractions (fECVs), which correlate with tissue fibrosis, and their relationships with DM and pre-DM (pDM).

MATERIAL AND METHODS

We included 100 consecutive patients with known or suspected liver and/or pancreatic diseases who underwent contrast-enhanced CT. Patients were classified as nondiabetes, pDM, and DM with hemoglobin A1c (HbA1c) levels of < 5.7%, 5.7%-6.5%, and ≥ 6.5% or fasting plasma glucose (FPG) levels of < 100, 100-125 mg/dL, and ≥ 126 mg/dL, respectively. Subtraction images between unenhanced and equilibrium-phase images were prepared. The liver and the pancreas were automatically extracted using a high-speed, three-dimensional image analysis system, and their respective mean CT values were calculated. The enhancement degree of the aorta (Δaorta) was measured. fECV was calculated using the following equation: fECV = (100 - hematocrit) * Δliver or pancreas/Δaorta. Differences were investigated in hepatic and pancreatic fECVs among the three groups, and the correlation between each two in hepatic fECV, pancreatic fECV, and HbA1c was determined.

RESULTS

The pancreatic fECV, which was positively correlated with the hepatic fECV and HbA1c (r = 0.51, P < 0.001, and r = 0.51, P < 0.001, respectively), significantly differed among the three groups (P < 0.001) and was significantly greater in DM than in pDM or nondiabetes and in pDM with nondiabetes (P < 0.001). Hepatic fECV was significantly greater in DM than in nondiabetes (P < 0.05).

CONCLUSION

The pancreatic fECV and pDM/DM are closely related.

A comparative study of synthetic and venous hematocrit for calculating cardiovascular magnetic resonance-derived extracellular volume

The extracellular volume (ECV) fraction derived from cardiac magnetic resonance (CMR) can reflect various pathologies. The application of ECVs was limited by the strict requirement that hematocrit (Hct0) should be obtained within 24 hours of CMR scan. The aim of this study was to obtain accurate and convenient ECV calculated from the venous Hct and synthetic Hct in CMR. A total of 839 subjects were retrospectively enrolled. The subjects were divided into derivation cohort for local sex-specific models and validation cohort for assessing the accuracy of different ECVs. In the validation cohort, venous Hcts from 7 days before the scan (Hct1 - 7), outside 7 days (Hct> 7), the closest day (Hctclosest), and Hctsyn were compared with Hct0. The agreement and correlation of the conventional ECV (ECV0) with the corresponding ECVs were analyzed. The factors affecting the accuracy of ECVsyn were assessed. ECV1-7 and ECVclosest had the best correlation and smallest bias with ECV0 (R = 0.959 and 0.951, bias = 0.02% and - 0.03%). When using an absolute 2% error as the standard, the performance of ECV1-7 was the best, with an accuracy of 81.0%, followed by ECVclosest (78.8%), ECV> 7 (77.2%) and ECVsyn (70.7%). Abnormally low and high Hcts and decreased left ventricular ejection fractions were associated with miscalculation of ECVsyn, especially patients with dilated cardiomyopathy. We recommend extending the time interval between a Hct and a CMR scan to 7 days for ECV calculation. The synthetic ECV should be used cautiously, especially for patients with extremely low or high Hcts, decreased cardiac function, and dilated cardiomyopathy.

Prediction of pancreatic fibrosis by dual-energy CT-derived extracellular volume fraction: Comparison with MRI

OBJECTIVES

To investigate the correlation between dual-energy CT (DECT) and MRI measurements of the extracellular volume fraction (ECV) and to assess the accuracy of both methods in predicting pancreatic fibrosis (PF).

METHODS

We retrospectively analyzed 43 patients who underwent pancreatectomy and preoperative pancreatic DECT and MRI between November 2018 and May 2022. The ECV was calculated using the T1 relaxation time (for MR-ECV) or absolute enhancement (for DECT-ECV) at equilibrium phase (180 s after contrast injection in our study). Pearson coefficient and Bland-Altman analysis were used to compare the correlation between the two ECVs, Spearman correlations were used to investigate the association between imaging parameters and PF, Receiver operating characteristic (ROC) curves were used to assess the diagnostic performance of the ECVs for advanced fibrosis (F2-F3), and multivariate logistic regression analysis was used to examine the relationship between PF and imaging parameters.

RESULTS

There was a strong correlation between DECT- and MR-derived ECVs (r = 0.948; p < 0.001). The two ECVs were positively correlated with PF (DECT: r = 0.647, p < 0.001; MR: r = 0.614, p < 0.001), and the mean values were 0.34 ± 0.08 (range: 0.22-0.62) and 0.35 ± 0.09 (range: 0.24-0.66), respectively. The area under the operating characteristic curve (AUC) for subjects with advanced fibrosis diagnosed by ECV was 0.86 for DECT-ECV and 0.87 for MR-ECV. Multivariate logistic regression analysis showed that the DECT-ECV was an independent predictor of PF.

CONCLUSIONS

The ECV could be an effective predictor of histological fibrosis, and DECT is equivalent to MRI for characterizing pancreatic ECV changes.

Tafamidis decreased cardiac amyloidosis deposition in patients with Ala97Ser hereditary transthyretin cardiomyopathy: a 12-month follow-up cohort study

BACKGROUND

Transthyretin cardiac cardiomyopathy (ATTR-CM) is a rare but life-threatening disease. Tafamidis is an effective treatment for patients with ATTR-CM, however its long-term effects on cardiac remodeling and cardiac amyloid deposition are unknown. This study aimed to used cardiac magnetic resonance (CMR) to investigate the effects of tafamidis on patients with hereditary A97S ATTR-CM.

METHODS

We retrospectively analyzed a prospective cohort of ATTR-CM patients, including 14 with hereditary A97S ATTR-CM and 17 healthy controls with baseline CMR data. All ATTR-CM patients received tafamidis treatment and received CMR with extracellular volume (ECV) at baseline and after 1 year of follow-up.

RESULTS

Baseline N-terminal pro-B-type natriuretic peptide, left ventricular (LV) mass, LV ejection fraction, global radial, circumferential and longitudinal strain, T1 mapping and ECV were significantly worse in the patients with ATTR-CM compared with the healthy controls. After 1 year of tafamidis treatment, ECV decreased from 51.5 ± 8.9% to 49.0 ± 9.4% (P = 0.041), however there were no significant changes in LV mass, LV ejection fraction, global radial strain, global circumferential strain, global longitudinal strain and T1 mapping.

CONCLUSIONS

After a one-year treatment period, tafamidis exhibited subtle but statistically significant reductions in ECV, potentially indicating a decrease in amyloid deposition among patients diagnosed with hereditary A97S ATTR-CM.

Quantification of myocardial extracellular volume without blood sampling

Aims

Cardiac magnetic resonance (CMR) T1 relaxation time mapping is an established technique primarily used to identify diffuse interstitial fibrosis and oedema. The myocardial extracellular volume (ECV) can be calculated from pre- and post-contrast T1 relaxation times and is a reproducible parametric index of the proportion of volume occupied by non-cardiomyocyte components in myocardial tissue. The conventional calculation of the ECV requires blood sampling to measure the haematocrit (HCT). Given the high variability of the HCT, the blood collection is recommended within 24 h of the CMR scan, limiting its applicability and posing a barrier to the clinical routine use of ECV measurements. In recent years, several research groups have proposed a method to determine the ECV by CMR without blood sampling. This is based on the inverse relationship between the T1 relaxation rate (R1) of blood and the HCT. Consequently, a 'synthetic' HCT could be estimated from the native blood R1, avoiding blood sampling.

Methods and results

We performed a review and meta-analysis of published studies on synthetic ECV, as well as a secondary analysis of previously published data to examine the effect of the chosen regression modell on bias. While, overall, a good correlation and little bias between synthetic and conventional ECV were found in these studies, questions regarding its accuracy remain.

Conclusion

Synthetic HCT and ECV can provide a 'non-invasive' quantitative measurement of the myocardium's extracellular space when timely HCT measurements are not available and large alterations in ECV are expected, such as in cardiac amyloidosis. Due to the dependency of T1 relaxation times on the local setup, calculation of local formulas using linear regression is recommended, which can be easily performed using available data.

Pancreatic fibrosis by extracellular volume fraction using Contrast-enhanced computed tomography and relationship with pancreatic cancer

PURPOSE

This study aimed to assess the relationship between pancreatic fibrosis measured by the extracellular volume fraction (ECV) using contrast-enhanced computed tomography (CT) and the histologic pancreatic fibrosis fraction and investigate the relationship between pancreatic fibrosis and pancreatic cancer.

METHOD

The study included 88 consecutive patients (48 males, 40 females; median age, 69 years; range, 17-89 years); 47 had pancreatic cancer, and 41 had other diseases. Fifty-two cases were evaluated pathologically for pancreatic fibrosis. The histologic pancreatic fibrosis fraction was quantified using image analysis software in nontumorous pancreatic tissue at the resection stump using 2-µm-thick Azan-stained slides. Two board-certified radiologists measured ECV in the pancreatic parenchyma at an estimated transection line. The correlation between histologic pancreatic fibrosis fraction and ECV was investigated, and whether the ECV value could be used as a biomarker for pancreatic cancer was investigated.

RESULTS

The histologic pancreatic fibrosis fraction was significantly correlated with the ECV (r = 0.64, P < 0.01). Pancreatic fibrosis evaluated by ECV was higher in pancreatic cancer patients than in other patients (P < 0.01). On receiver-operating characteristic curve analysis, the ECV had good diagnostic accuracy for the development of pancreatic cancer (cut-off value 32.8%; sensitivity 61.0%, specificity 85.1%). ECV was identified on multivariate analysis as an independent risk factor for pancreatic cancer (odds ratio 1.16; P < 0.01).

CONCLUSIONS

Extracellular volume fraction was strongly related to the histologic pancreatic fibrosis fraction, which was independently associated with pancreatic cancer. Thus, extracellular volume fraction is an imaging biomarker that reflects the progression of pancreatic fibrosis and may potentially help predict the development of pancreatic cancer, although further investigation will be needed.

Phantom-based correction for standardization of myocardial native T1 and extracellular volume fraction in healthy subjects at 3-Tesla cardiac magnetic resonance imaging

OBJECTIVES

To investigate the effect of the phantom-based correction method for standardizing myocardial native T1 and extracellular volume fraction (ECV) in healthy subjects.

METHODS

Seventy-one healthy asymptomatic adult (≥ 20 years) volunteers of five different age groups (34 men and 37 women, 45.5 ± 15.5 years) were prospectively enrolled in three academic hospitals. Cardiac MRI including Modified Look - Locker Inversion recovery T1 mapping sequence was performed using a 3-Tesla system with a different type of scanner for each hospital. Native T1 and ECV were measured in the short-axis T1 map and analyzed for mean values of the 16 entire segments. The myocardial T1 value of each subject was corrected based on the site-specific equation derived from the T1 Mapping and ECV Standardization phantom. The global native T1 and ECV were compared between institutions before and after phantom-based correction, and the variation in native T1 and ECV among institutions was assessed using a coefficient of variation (CoV).

RESULTS

The global native T1 value significantly differed between the institutions (1198.7 ± 32.1 ms, institution A; 1217.7 ± 39.9 ms, institution B; 1232.7 ± 31.1 ms, institution C; p = 0.002), but the mean ECV did not (26.6-27.5%, p = 0.355). After phantom-based correction, the global native T1 and ECV were 1289.7 ± 32.4 ms and 25.0 ± 2.7%, respectively, and CoV for native T1 between the three institutions decreased from 3.0 to 2.5%. The corrected native T1 value did not significantly differ between institutions (1284.5 ± 31.5 ms, institution A; 1296.5 ± 39.1 ms, institution B; 1291.3 ± 29.3 ms, institution C; p = 0.440), and neither did the ECV (24.4-25.9%, p = 0.078).

CONCLUSIONS

The phantom-based correction method can provide standardized reference T1 values in healthy subjects.

KEY POINTS

• After phantom-based correction, the global native T1 of 16 entire myocardial segments on 3-T cardiac MRI is 1289.4 ± 32.4 ms, and the extracellular volume fraction was 25.0 ± 2.7% for healthy subjects. • After phantom - based correction was applied, the differences in the global native T1 among institutions became insignificant, and the CoV also decreased from 3.0 to 2.5%.

Synthetic Extracellular Volume in Cardiac Magnetic Resonance Without Blood Sampling: a Reliable Tool to Replace Conventional Extracellular Volume

Background:

The calculation of extracellular volume (ECV) in cardiac magnetic resonance requires hematocrit, limiting its applicability in clinical practice. Based on the linear relationship between hematocrit and blood T1 relaxivity, a synthetic ECV could be estimated without a blood sample. We aim to develop and test regression models for synthetic ECV without blood sampling in 1.5-T and 3.0-T scanners.

Methods:

A total of 1101 subjects who underwent cardiac magnetic resonance scanning with native and postcontrast T1 mapping and venous hematocrit within 24 hours were retrospectively enrolled. Subjects were randomly split into derivation (n=550) and validation (n=551) subgroups for each scanner. Different regression models were derived controlling for sex, field strength, and left ventricle/right ventricle blood pool and validated in the validation group. We performed additional validation analyses in subgroups of patients with histological validation (n=17), amyloidosis (n=29), anemia (n=185), and reduced ejection fraction (n=322).

Results:

In the derivation group, 8 specific models and 2 common estimate models were derived. In the validation group, using specific models, synthetic ECV had high agreement with conventional ECV (R², 0.87; P<0.0001 and R², 0.88, P<0.0001; −0.16% and −0.10%, left ventricle and right ventricle model, respectively). Common models also performed well (R², 0.88; P<0.0001 and R², 0.89, P<0.0001; −0.21% and −0.18%, left ventricle and right ventricle model, respectively). Histological validation demonstrated equal performance of synthetic and measured ECV. Synthetic ECV as calculated by the common model showed a bias in the anemia cohort significantly reduced by the specific model (−2.45 to −1.28, right ventricle common and specific model, respectively).

Conclusions:

Synthetic ECV provided a promising way to calculate ECV without blood sampling. Specific models could provide the most accurate value, while common models could be more suitable in routine clinical practice because of their simplicity while maintaining adequate accuracy.

Performance of Synthetic Extracellular Volume Fraction in Different Cardiac Phenotypes From a Prospective Cohort of Patients Referred for Cardiac Magnetic Resonance

BACKGROUND

A synthetic myocardial extracellular volume fraction (sECV) can be obtained without blood hematocrit (Hct) by using the linear relationship between Hct and the longitudinal relaxation time of blood. Concerns have been raised about the widespread clinical application of this approach.

PURPOSE

To assess the relationship between measured ECV (m-ECV) and sECV, using both a published model and a locally derived one.

STUDY TYPE

Single-center, prospective.

FIELD STRENGTH/SEQUENCE

A 1.5 T/modified Look Locker (MOLLI) sequence.

SUBJECTS

Fifty-two healthy subjects and 113 patients (76 with and 37 without a hypertrophic cardiac phenotype).

ASSESSMENT

Three ECV values were obtained for each patient: 1) measured ECV (m-ECV), using Hct from a venous blood sample; 2) Fent-synthetic ECV (F-sECV), using the equation proposed by Fent et al; and 3) Local-synthetic ECV (L-sECV), using the equation obtained from a local derivation cohort comprising 83 subjects.

STATISTICAL TESTS

Shapiro-Wilk test, analysis of variance, Kruskal Wallis test, Pearson correlation, Bland-Altman analysis, univariate and multivariable regression analysis.

RESULTS

In the validation cohort (N = 82), Bland-Altmann analysis revealed an excellent agreement between m-ECV and L-sECV with a statistically insignificant bias (-0.1%, limits of agreement: -2.8% and 2.6%; P = 0.528), while in the overall population (N = 165), the mean bias between m-ECV and F-sECV was small but significant (1.2%, limits of agreement: -1.5% and 3.9%, P < 0.05). F-sECV bias was significantly higher for measured Hct (m-Hct) values <0.372 (2.3% vs. 1.0%, P < 0.05). Among the phenotype subgroups, amyloidotic patients showed a higher bias compared to others, both with F-sECV and L-sECV (2.3% vs. 1.1%, P < 0.05 and 1.1% vs. 0.2%, P < 0.05, respectively).

DATA CONCLUSION

Although synthetic ECV performs well in an external cohort, the use of a local formula further improves the accuracy of ECV estimate over a broad spectrum of cardiac phenotypes. Local sECV performs better for a wider range of Hct values, compared to the published model. Amyloidosis is the only group associated with a lower accuracy.

LEVEL OF EVIDENCE

5 TECHNICAL EFFICACY: Stage 2.