The Cognitive Ageing, Nutrition and Neurogenesis (CANN) trial: Design and progress.

INTRODUCTION: The Cognitive Ageing, Nutrition and Neurogenesis trial hypothesizes that a combined intervention with long-chain n-3 polyunsaturated fatty acids (n-3) and cocoa flavan-3-ols (FLAV) will mitigate the cognitive decline anticipated to naturally occur over 1 year in older adults. METHODS: In a double-blinded, placebo-controlled parallel design, 259 individuals with mild cognitive impairment or subjective memory impairment were randomized to a control or n-3 FLAV group (1.5 g docosahexaenoic acid + eicosapentaenoic acid and 500 mg n-3 FLAV daily) for 12 months. Cognition was measured at 0, 3, and 12 months. The primary end-point is hippocampus-sensitive cognitive function (e.g., number of false-positives on the Picture Recognition Task of the Cognitive Drug Research test battery). Secondary outcomes include additional cognitive measures, brain atrophy and blood flow (assessed by magnetic resonance imaging), vascular function, circulating biomarkers of cardiovascular and cognitive health, gut microflora, red blood cell fatty acid status, and urine flavan-3-ol metabolites. RESULTS: Screening began in 2015, with all baseline visits completed in March 2017. The intervention was finished in March 2018. DISCUSSION: Cognitive Ageing, Nutrition and Neurogenesis aims to identify an effective diet-based intervention to prevent or delay cognitive impairment in cognitively at-risk individuals, which could ultimately contribute to a reduced population burden of dementia. CLINICALTRIALSGOV: NCT02525198.

Accuracy of high b-value diffusion-weighted MRI for prostate cancer detection: a meta-analysis.

Background The diagnostic accuracy of diffusion-weighted imaging (DWI) to detect prostate cancer is well-established. DWI provides visual as well as quantitative means of detecting tumor, the apparent diffusion coefficient (ADC). Recently higher b-values have been used to improve DWI's diagnostic performance. Purpose To determine the diagnostic performance of high b-value DWI at detecting prostate cancer and whether quantifying ADC improves accuracy. Material and Methods A comprehensive literature search of published and unpublished databases was performed. Eligible studies had histopathologically proven prostate cancer, DWI sequences using b-values ≥ 1000 s/mm2, less than ten patients, and data for creating a 2 × 2 table. Study quality was assessed with QUADAS-2 (Quality Assessment of diagnostic Accuracy Studies). Sensitivity and specificity were calculated and tests for statistical heterogeneity and threshold effect performed. Results were plotted on a summary receiver operating characteristic curve (sROC) and the area under the curve (AUC) determined the diagnostic performance of high b-value DWI. Results Ten studies met eligibility criteria with 13 subsets of data available for analysis, including 522 patients. Pooled sensitivity and specificity were 0.59 (95% confidence interval [CI], 0.57-0.61) and 0.92 (95% CI, 0.91-0.92), respectively, and the sROC AUC was 0.92. Subgroup analysis showed a statistically significant ( P = 0.03) improvement in accuracy when using tumor visual assessment rather than ADC. Conclusion High b-value DWI gives good diagnostic performance for prostate cancer detection and visual assessment of tumor diffusion is significantly more accurate than ROI measurements of ADC.

An improved model for prostate diffusion incorporating the results of Monte Carlo simulations of diffusion in the cellular compartment.

The purpose of this work was to refine a previously published model of prostate diffusion by incorporating improved estimates of cellular diffusivity obtained by Monte Carlo simulation. Stromal and epithelial cell size and intracellular volume fraction in different grades of cancer were determined from histological images. Diffusion in different mixtures of cells, corresponding to different tumor grades, was simulated and cellular apparent diffusion coefficient and kurtosis values determined. These values were incorporated into the previously published model of prostate diffusion and model predictions compared with values found in the literature. Stromal cell radius and intracellular volume fraction were 3.74 ± 0.96 µm and 13 ± 3% respectively in normal peripheral zone (PZ), and were similar in all grades of cancer. Epithelial cell radius and intracellular volume fraction were 3.40 ± 0.15 µm and 45 ± 5% respectively in normal PZ, rising to 4.75 ± 0.20 µm and 70 ± 8% in high grade cancer. Cellular apparent diffusion coefficient and kurtosis were 1.02 µm2 ms-1 and 0.58 respectively in normal PZ, and 0.61 µm2 ms-1 and 1.15 in high grade cancer (variation in simulation values are less than 0.1%). Agreement between model predictions and measurements were good, with a mean square error of 0.22 µm2 ms-1 . Incorporation of cellular diffusion coefficient and kurtosis values obtained by Monte Carlo simulation into a model of prostate diffusion gives good agreement with published results.

A model describing diffusion in prostate cancer.

PURPOSE: Quantitative diffusion MRI has frequently been studied as a means of grading prostate cancer. Interpretation of results is complicated by the nature of prostate tissue, which consists of four distinct compartments: vascular, ductal lumen, epithelium, and stroma. Current diffusion measurements are an ill-defined weighted average of these compartments. In this study, prostate diffusion is analyzed in terms of a model that takes explicit account of tissue compartmentalization, exchange effects, and the non-Gaussian behavior of tissue diffusion. METHOD: The model assumes that exchange between the cellular (ie, stromal plus epithelial) and the vascular and ductal compartments is slow. Ductal and cellular diffusion characteristics are estimated by Monte Carlo simulation and a two-compartment exchange model, respectively. Vascular pseudodiffusion is represented by an additional signal at b = 0. Most model parameters are obtained either from published data or by comparing model predictions with the published results from 41 studies. Model prediction error is estimated using 10-fold cross-validation. RESULTS: Agreement between model predictions and published results is good. The model satisfactorily explains the variability of ADC estimates found in the literature. CONCLUSION: A reliable model that predicts the diffusion behavior of benign and cancerous prostate tissue of different Gleason scores has been developed. Magn Reson Med 78:316-326, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

A monte carlo study of restricted diffusion: Implications for diffusion MRI of prostate cancer.

PURPOSE: Diffusion MRI is used frequently to assess prostate cancer. The prostate consists of cellular tissue surrounding fluid filled ducts. Here, the diffusion properties of the ductal fluid alone were studied. Monte Carlo simulations were used to investigate ductal residence times to determine whether ducts can be regarded as forming a separate compartment and whether ductal radius could determine the Apparent Diffusion Coefficient (ADC) of the ductal fluid. METHODS: Random walks were simulated in cavities. Average residence times were estimated for permeable cavities. Signal reductions resulting from application of a Stejskal-Tanner pulse sequence were calculated in impermeable cavities. Simulations were repeated for cavities of different radii and different diffusion times. RESULTS: Residence times are at least comparable with diffusion times even in relatively high grade tumors. ADCs asymptotically approach theoretical limiting values. At large radii and short diffusion times, ADCs are similar to free diffusion. At small radii and long diffusion times, ADCs are reduced toward zero, and kurtosis approaches a value of -1.2. CONCLUSIONS: Restricted diffusion in cavities of similar sizes to prostate ducts may reduce ductal ADCs. This may contribute to reductions in total ADC seen in prostate cancer. Magn Reson Med 77:1671-1677, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Parameter Estimation Error Dependency on the Acquisition Protocol in Diffusion Kurtosis Imaging.

Mono-exponential kurtosis model is routinely fitted on diffusion weighted, magnetic resonance imaging data to describe non-Gaussian diffusion. Here, the purpose was to optimize acquisitions for this model to minimize the errors in estimating diffusion coefficient and kurtosis. Similar to a previous study, covariance matrix calculations were used, and coefficients of variation in estimating each parameter of this model were calculated. The acquisition parameter, b values, varied in discrete grids to find the optimum ones that minimize the coefficient of variation in estimating the two non-Gaussian parameters. Also, the effect of variation of the target values on the optimized values was investigated. Additionally, the results were benchmarked with Monte Carlo noise simulations. Simple correlations were found between the optimized b values and target values of diffusion and kurtosis. For small target values of the two parameters, there is higher chance of having significant errors; this is caused by maximum b value limits imposed by the scanner than the mathematical bounds. The results here, cover a wide range of parameters D and K so that they could be used in many directionally averaged diffusion weighted cases such as head and neck, prostate, etc.

Does Magnetic Resonance Brain Scanning at 3.0 Tesla Pose a Hyperthermic Challenge to Term Neonates?

Next-generation 3-Tesla magnetic resonance (MR) scanners offer improved neonatal neuroimaging, but the greater associated radiofrequency radiation may increase the risk of hyperthermia. Safety data for neonatal 3-T MR scanning are lacking. We measured rectal temperatures continuously in 25 neonates undergoing 3-T brain MR imaging and observed no significant hyperthermic threat.

MRI texture analysis of subchondral bone at the tibial plateau.

OBJECTIVES: To determine the feasibility of MRI texture analysis as a method of quantifying subchondral bone architecture in knee osteoarthritis (OA). METHODS: Asymptomatic subjects aged 20-30 (group 1, n = 10), symptomatic patients aged 40-50 (group 2, n = 10) and patients scheduled for knee replacement aged 55-85 (group 3, n = 10) underwent high spatial resolution T1-weighted coronal 3T knee MRI. Regions of interest were created in the medial (MT) and lateral (LT) tibial subchondral bone from which 20 texture parameters were calculated. T2 mapping of the tibial cartilage was performed in groups 1 and 2. Mean parameter values were compared between groups using ANOVA. Linear discriminant analysis (LDA) was used to evaluate the ability of texture analysis to classify subjects correctly. RESULTS: Significant differences in 18/20 and 12/20 subchondral bone texture parameters were demonstrated between groups at the MT and LT respectively. There was no significant difference in mean MT or LT cartilage T2 values between group 1 and group 2. LDA demonstrated subject classification accuracy of 97 % (95 % CI 91-100 %). CONCLUSION: MRI texture analysis of tibial subchondral bone may allow detection of alteration in subchondral bone architecture in OA. This has potential applications in understanding OA pathogenesis and assessing response to treatment. KEY POINTS: • Improved techniques to monitor OA disease progression and treatment response are desirable • Subchondral bone (SB) may play significant role in the development of OA • MRI texture analysis is a method of quantifying changes in SB architecture • Pilot study showed that this technique is feasible and reliable • Significant differences in SB texture were demonstrated between individuals with/without OA.

Quantitative analysis of tibial subchondral bone: Texture analysis outperforms conventional trabecular microarchitecture analysis.

BACKGROUND: The aim of this study was to compare two different methods of quantitative assessment of tibial subchondral bone in osteoarthritis (OA): statistical texture analysis (sTA) and trabecular microarchitecture analysis (tMA). METHODS: Asymptomatic controls aged 20-30 (n = 10), patients aged 40-50 with chronic knee pain but without established OA (n = 10) and patients aged 55-85 with advanced OA scheduled for knee replacement (n = 10) underwent knee MR imaging at 3 Tesla with a three-dimensional gradient echo sequence to allow sTA and tMA. tMA and sTA features were calculated using region of interest creation in the medial (MT) and lateral (LT) tibial subchondral bone. Features were compared between groups using one-way analysis of variance. The two most discriminating tMA and sTA features were used to construct exploratory discriminant functions to assess the ability of the two methods to classify participants. RESULTS: No tMA features were significantly different between groups at either MT or LT. 17/20 and 11/20 sTA features were significantly different between groups at the MT/LT, respectively (P < 0.001). Discriminant functions created using tMA features classified 12/30 participants correctly (40% accuracy; 95% confidence interval [CI], 22-58%) based on MT data and 9/30 correctly (30%,; 95% CI, 14-46) based on LT data. Discriminant functions using sTA features classified 16/30 participants correctly (53%; 95% CI, 35-71) based on MT data and 14/30 correctly (47%; 95% CI, 29-65) based on LT data. CONCLUSION: sTA features showed more significant differences between the three study groups and improved classification accuracy compared with tMA features.

Pharmacokinetic modeling of multislice dynamic contrast-enhanced MRI in normal-healing radial fractures: A pilot study.

PURPOSE: To define the range of quantitative pharmacokinetic parameters in normal-healing bone with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). DCE-MRI is an established technique for characterizing abnormal tissue microvasculature within solid tumors, but has also shown promise for assessing bone and bone marrow. MATERIALS AND METHODS: In this study ethical approval for eight patients was obtained. Inclusion criteria were an extra-articular distal radial fracture in patients aged 20-50 years which had united by 6 weeks in plaster cast. This was assessed by an experienced orthopedic surgeon. DCE-MRI was performed at 1.5T 6 weeks after initial injury. The transfer constant (K(trans) ), transfer rate (Kep ), and initial area under the curve (IAUC) values for the fracture site and adjacent marrow were obtained for each patient. RESULTS: The mean T1 , K(trans) , Kep , and IAUC at the fracture site were 1713 (standard deviation [SD] 645), 0.09 (SD 0.07), 0.17 (SD 0.17) and 4.9 (SD 4.4). The relative standard deviation (RSD) for the fracture site ranged from 0.38 to 0.97 and for the adjacent marrow ranged from 0.95-3.88. Within each patient the range of RSDs was 0.04-0.42 for T1 , 0.26-0.91 for K(trans) , 0.14-1.06 for Kep , and 0.35-0.96 for the IAUC. CONCLUSION: Pharmacokinetic measures of perfusion can be obtained from healing fractures using DCE-MRI with "excellent" intraclass correlation coefficients for inter- and intrarater reliability. The use of these perfusion parameters is limited by wide patient-to-patient variation and slice-to-slice variation within patients.

Minimization of errors in biexponential T2 measurements of the prostate.

PURPOSE: To determine the echo times that provide the greatest precision in measurements of prostate T2s. T2 relaxation time measurements in the prostate are complicated by the structure of prostate tissue, which consists of fluid-filled glands surrounded by epithelial and stromal cells. Since the glands are large relative to diffusion distances, there is little water exchange between the two compartments and T2s are biexponential. Because the relative size and characteristics of the two compartments change in prostate tumors, accurate measurement of the characteristics of each may provide useful information on tumor grade. MATERIALS AND METHODS: T2s were measured in a group of 25 men with biopsy-proven prostate cancer. Subjects were scanned at 3T with a 16-echo turbo-spin echo T2-mapping sequence. Normal prostate T2s were measured in areas showing no disease. Optimum echo times for measurement of normal prostate T2s were found by calculating the covariance matrix, which provides estimates of parameter variance. Echo times that minimize T2 variance were then found by searching over grids of different echo times. Optima for four to eight echo acquisitions were found. Optima were tested by Monte Carlo simulation. RESULTS: Fast and slow T2s were 60 msec and 360 msec, respectively. The fast signal fraction was 0.6. Optimum echo times were between 0 and 780 msec, depending on the number of echoes acquired. CONCLUSION: Use of optimum echo times can substantially improve the precision of biexponential T2 measurements. This optimization is anticipated to improve prostate cancer characterization using T2 measurements.

Analytical derivation of the b matrix of a time-efficient isotropic diffusion weighting gradient waveform.

PURPOSE: Diffusion-weighted magnetic resonance imaging of (3)He provides information about lung structure. If rotationally invariant measures of diffusion are desired, an equal diffusion weighting in all three spatial directions is necessary to obtain. In order to achieve such isotropic diffusion weighting, gradients have to be applied in these three spatial directions, which can be time consuming. Therefore, the purpose of this study was the analytic derivation of a time-efficient isotropic diffusion weighting scheme. METHODS: The complete b matrix of a preselected gradient waveform was derived analytically. The effect of ramp times and the contribution of the imaging gradients were included in the calculation. The time-efficient waveform was compared to a standard isotropic diffusion weighting scheme by determining the mean diffusivity of hyperpolarized (3)He in human lungs. RESULTS: An analytically derived expression of the b matrix for a time-efficient gradient scheme allowing isotropic diffusion weighting was derived. Additionally, the b matrix of a common set of imaging gradients was calculated. Diffusion measurements of hyperpolarized (3)He in human lungs using the derived optimized gradient scheme and a standard gradient waveform used for isotropic diffusion weighting, respectively, gave results for the mean diffusivity which did not show any statistical difference. However, the echo time using the optimized scheme was reduced by 2.5 ms in comparison with the standard scheme which leads to a theoretical signal increase of 30%. CONCLUSIONS: The analytically derived b matrix allows for the straightforward determination of time-efficient isotropic diffusion weighting schemes. By using those schemes, a substantial gain in signal can be achieved whereas the resulting values for the mean diffusivity did not show any statistical difference to the values obtained when using standard waveforms for isotropic diffusion weighting.

ΔR2 (*) gadolinium-diethylenetriaminepentacetic acid relaxivity in venous blood.

The accuracy of perfusion measurements using dynamic, susceptibility-weighted, contrast-enhanced MRI depends on estimating contrast agent concentration in an artery, i.e., the arterial input function. One of the difficulties associated with obtaining an arterial input function are partial volume effects when both blood and brain parenchyma occupy the same pixel. Previous studies have attempted to correct arterial input functions which suffer from partial volume effects using contrast concentration in venous blood. However, the relationship between relaxation and concentration (C) in venous blood has not been determined in vivo. In this note, a previously employed fitting approach is used to determine venous relaxivity in vivo. In vivo relaxivity is compared with venous relaxivity measured in vitro in bulk blood. The results show that the fitting approach produces relaxivity calibration curves which give excellent agreement with arterial measurements.

Intravascular contrast agent T2* relaxivity in brain tissue.

Dynamic susceptibility-weighted contrast-enhanced (DSC) MRI perfusion measurements depend on estimating intravascular contrast agent (CA) concentrations (C) from signal intensity changes in T2*-weighted images after bolus injection. Generally, linearity is assumed between relaxation and C, but previous studies have shown that compartmentalization of CA and secondary magnetic field perturbations generate deviations from linearity. Physical phantoms using bulk blood have been used to empirically determine the relationship between relaxation rate and C in large vessels. However, the relaxivity of CA in the microvasculature is not easily measured since constructing appropriate phantoms is difficult. Instead, theoretical relaxivity models have been developed. In this study, we empirically tested a non-linear expression based on static dephasing regime (SDR) and linear approximation. Signal-time curves in white (WM) and grey matter (GM) were converted to concentration time curves (CTCs) using both expressions. Parameters for both linear and non-linear formulations were adjusted to give a best agreement between cerebral blood volumes (CBV) calculated from WM and arterial CTCs in a group of normal subjects scanned at 3T. Optimized parameters were used to calculate blood volume in WM and GM in healthy subjects scanned at 3T and in meningioma patients scanned at 1.5T. Results from this study showed that a non-linear SDR formulation gave an acceptable functional form for tissue relaxivity, giving reliable CBV estimates at different field strengths and echo times.

Prostate cancer: feasibility and preliminary experience of a diffusional kurtosis model for detection and assessment of aggressiveness of peripheral zone cancer.

PURPOSE: To assess the feasibility of diffusional kurtosis (DK) imaging for distinguishing benign from malignant regions, as well as low- from high-grade malignant regions, within the peripheral zone (PZ) of the prostate in comparison with standard diffusion-weighted (DW) imaging. MATERIALS AND METHODS: The institutional review board approved this retrospective HIPAA-compliant study and waived informed consent. Forty-seven patients with prostate cancer underwent 3-T magnetic resonance imaging by using a pelvic phased-array coil and DW imaging (maximum b value, 2000 sec/mm2). Parametric maps were obtained for apparent diffusion coefficient (ADC); the metric DK (K), which represents non-Gaussian diffusion behavior; and corrected diffusion (D) that accounts for this non-Gaussianity. Two radiologists reviewed these maps and measured ADC, D, and K in sextants positive for cancer at biopsy. Data were analyzed by using mixed-model analysis of variance and receiver operating characteristic curves. RESULTS: Seventy sextants exhibited a Gleason score of 6; 51 exhibited a Gleason score of 7 or 8. K was significantly greater in cancerous sextants than in benign PZ (0.96±0.24 vs 0.57±0.07, P<.001), as well as in cancerous sextants with higher rather than lower Gleason score (1.05±0.26 vs 0.89±0.20, P<.001). K showed significantly greater sensitivity for differentiating cancerous sextants from benign PZ than ADC or D (93.3% vs 78.5% and 83.5%, respectively; P<.001), with equal specificity (95.7%, P>.99). K exhibited significantly greater sensitivity for differentiating sextants with low- and high-grade cancer than ADC or D (68.6% vs 51.0% and 49.0%, respectively; P≤.004) but with decreased specificity (70.0% vs 81.4% and 82.9%, respectively; P≤.023). K had significantly greater area under the curve for differentiating sextants with low- and high-grade cancer than ADC (0.70 vs 0.62, P=.010). Relative contrast between cancerous sextants and benign PZ was significantly greater for D or K than ADC (0.25±0.14 and 0.24±0.13, respectively, vs 0.18±0.10; P<.001). CONCLUSION: Preliminary findings suggest increased value for DK imaging compared with standard DW imaging in prostate cancer assessment.

Treatment-related change versus tumor recurrence in high-grade gliomas: a diagnostic conundrum--use of dynamic susceptibility contrast-enhanced (DSC) perfusion MRI.

OBJECTIVE: The purpose of this article is to address radiation necrosis, pseudoprogression, and pseudoresponse relative to high-grade gliomas and evaluate the role of conventional MRI and, in particular, dynamic susceptibility contrast-enhanced perfusion MRI in assessing such treatment-related changes from tumor recurrence. CONCLUSION: Posttreatment imaging assessment of high-grade gliomas remains challenging. Familiarity with the expected MR imaging appearances of treatment-related change and tumor recurrence will help distinguish these entities allowing appropriate management.

An improved model for describing the contrast bolus in perfusion MRI.

PURPOSE: Quantification of perfusion measurements using dynamic, susceptibility-weighted contrast-enhanced (DSC) MRI depends on estimating the size and shape of the tracer bolus. Typically, the bolus is described as a gamma variate function (GV) fitted to the bolus portion of tracer concentration time curve (CTC). However, the last point to fit is arbitrary which can lead to considerable variation in the fitted curve in the presence of noise. In this technical note, we present a model which takes into account recirculation explicitly and fits robustly to the entire CTC in the presence of noise. METHODS: Signal data measurements from ten DSC MRI patients were fitted with our new model and a GV function using four different methods of estimating the end of the bolus. Estimates of the area under the curves (AUC) and first moments (FMs) of the bolus were compared at different noise levels. RESULTS: The new model gave errors similar to or smaller than those of the most effective methods for fitting a GV. CONCLUSIONS: The single compartment recirculation (SCR) model is the most robust fitting technique with respect to noise both for bias and variability.

Relative cerebral blood volume measurements of low-grade gliomas predict patient outcome in a multi-institution setting.

BACKGROUND/PURPOSE: The prognostic value of defining subcategories of gliomas is still controversial. This study aims to determine the utility of relative cerebral blood volume (rCBV) in predicting clinical response in patients with low-grade glioma at multiple institutions. MATERIALS AND METHODS: Sixty-nine patients were studied with dynamic susceptibility contrast-enhanced perfusion MRI at two institutions. The pathologic diagnoses of the low-grade gliomas were 34 astrocytomas, 20 oligodendroglioma, 9 oligoastrocytomas, 1 ganglioglioma and 5 with indeterminate histology. Wilcoxon tests were used to compare patients in different response categories with respect to baseline rCBV. Kaplan-Meier curve and log-rank tests were used to predict the association of rCBV with time to progression. RESULTS: At both institutions, patients with an adverse event (progressive disease or death) had a significantly higher baseline rCBV than those without (complete response or stable disease) (p value=0.0138). The odds ratio for detecting an adverse event when using rCBV was 1.87 (95% confidence interval: 1.14-3.08). rCBV was significantly negatively associated with time to progression (p=0.005). The median time to progression among subjects with rCBV>1.75 was 365 days, while there was 95% confidence that the median time to progression was at least 889 days among subjects with rCBV<1.75. CONCLUSION: Our study suggests not only that rCBV measurements correlate well with time to progression or death, but also that the findings can be replicated across institutions, which supports the application of rCBV as an adjunct to pathology in predicting glioma biology.

Robust quantification of contrast agent (CA) concentration with magnetic field correlation (MFC) imaging.

Contrast-enhanced perfusion studies of the brain by means magnetic resonance imaging (MRI) are used to estimate a number of important brain tissue parameters, including cerebral blood flow and volume. In order to calculate these parameters, the contrast agent (CA) concentration must first be estimated. This is usually accomplished by measurement of a nuclear magnetic resonance (NMR) relaxation rate with the assumption of a linear relationship between the rate and the CA concentration. However, such a linear relationship does not necessarily hold in biological tissues due to compartmentalization of the CA in either the intravascular or extracellular spaces. Here we propose an alternative MRI method of CA quantification based on measurement of the magnetic field correlation (MFC), which is theoretically predicted to have a robust quadratic dependence on the CA concentration even when the CA is compartmentalized. In this study, CA concentration estimation by means of MFC is shown to be more accurate than established methods based on relaxation rates in yeast cell suspensions.