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In vivo assessment of optimal b-value range for perfusion-insensitive apparent diffusion coefficient imaging.

ABSTRACT: To assess the optimal b-values range for perfusion-insensitive apparent diffusion coefficient (ADC) imaging of abdominal organs using short-duration DW-MRI acquisitions with currently available ADC estimation methods.DW-MRI data of 15 subjects were acquired with eight b-values in the range of 5-800 s∕mm(2). The reference-standard, a perfusion insensitive, ADC value (ADC(IVIM)), was computed using an intravoxel incoherent motion (IVIM) model with all acquired diffusion-weighted images. Simulated DW-MRI data was generated using an IVIM model with b-values in the range of 0-1200 s∕mm(2). Monoexponential ADC estimates were calculated using: (1) Two-point estimator (ADC(2)); (2) least squares three-point (ADC(3)) estimator and; (3) Rician noise model estimator (ADC(R)). The authors found the optimal b-values for perfusion-insensitive ADC calculations by minimizing the relative root mean square error (RRMS) between the ADC(IVIM) and the monoexponential ADC values for each estimation method and organ.Low b-value = 300 s∕mm(2) and high b-value = 1200 s∕mm(2) minimized the RRMS between the estimated ADC and the reference-standard ADC(IVIM) to less than 5% using the ADC(3) estimator. By considering only the in vivo DW-MRI data, the combination of low b-value = 270 s∕mm(2) and high b-value of 800 s∕mm(2) minimized the RRMS between the estimated ADC and the reference-standard ADC(IVIM) to <7% using the ADC(3) estimator. For all estimators, the RRMS between the estimated ADC and the reference standard ADC correlated strongly with the perfusion-fraction parameter of the IVIM model (r = [0.78-0.83], p ≤ 0.003).The perfusion compartment in DW-MRI signal decay correlates strongly with the RRMS in ADC estimates from short-duration DW-MRI. The impact of the perfusion compartment on ADC estimations depends, however, on the choice of b-values and estimation method utilized. Likewise, perfusion-related errors can be reduced to <7% by carefully selecting the b-values used for ADC calculations and method of estimation.

SUBMITTER: Freiman M

PROVIDER: S-EPMC3411587 | biostudies-other | 2012 Aug

REPOSITORIES: biostudies-other

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Project description:BackgroundSuspicious breast lesions [Breast Imaging Reporting and Data System (BI-RADS) category 4 or 5] detected only by magnetic resonance imaging (MRI) and invisible on other initial imaging modalities (MRI-only lesions) are usually small and poorly characterized in previous literature, thus making diagnosis and management difficult. This study aimed to investigate the clinical significance of quantitative apparent diffusion coefficient (ADC) metrics derived from conventional diffusion-weighted imaging (DWI) on evaluating MRI-only lesions.MethodsA total of 90 suspicious MRI-only lesions were evaluated, including 51 malignant and 39 benign lesions. Morphological and kinetic characteristics of all lesions (termed BI-RADS parameters) were described according to the BI-RADS lexicon on dynamic contrast-enhanced (DCE) imaging. Minimum, maximum, and mean ADC values (ADCmin, ADCmax, ADCmean) were obtained by measuring the ADC map of DWI. ADCheterogeneity was then obtained by the following formula: ADCheterogeneity = (ADCmax - ADCmin)/ADCmean. Diagnostic performance of these parameters was assessed and compared using the receiver operating characteristic (ROC) curve.ResultsOf the 90 MRI-only lesions, there were 45 masses and 45 non-mass lesions. Among BI-RADS parameters, only two different kinetic patterns were significantly different between benign and malignant groups (P=0.005 and P<0.001, respectively). The area under the ROC curve (AUC) of combined significant ADC parameters (ADCmin, ADCmean, and ADCmax, all P≤0.001) was significantly higher than that of the two different kinetic patterns (P=0.006 for both). For MRI-only masses, only ADCmean and ADCmax, among all BI-RADS and ADC parameters, had diagnostic value (combined AUC =0.833). For non-mass lesions, size, distribution, ADCmin, and ADCmean were significantly different between benign and malignant groups (P=0.004, P<0.001, P=0.001, and P<0.001, respectively). In addition, ADCmean had the highest diagnostic performance among all ADC parameters, regardless of mass or non-mass (AUC =0.825 and 0.812, respectively). ADCheterogeneity showed no significant differences, no matter in mass or non-mass groups (P=0.62 and 0.43, respectively).ConclusionsIn differentiating MRI-only suspicious lesions, quantitative ADC metrics generally performed better than BI-RADS parameters, and ADCmean is still the best ADC parameter to distinguish MRI-only lesions.

Project description:BackgroundThe efficacy of neoadjuvant chemotherapy is closely related to the long-term prognosis of colorectal cancer (CRC) patients. Apparent diffusion coefficient (ADC) is an index in dynamic enhanced magnetic resonance imaging (MRI), reflecting the density of tumor cells. ADC has been shown to be related to the efficacy of neoadjuvant chemotherapy in other malignant tumors, but there is still a lack of relevant research in CRC patients.MethodsA total of 128 patients with CRC treated with neoadjuvant chemotherapy in The First Affiliated Hospital of Xiamen University from January 2016 to January 2017 were retrospectively collected. According to the response after neoadjuvant chemotherapy, the patients were divided into an objective response group (n=80) and a control group (n=48). The clinical characteristics and ADC levels of the two groups were compared, and the predictive value of ADC on the efficacy of neoadjuvant chemotherapy was analyzed. The patients were followed up for 5 years to observe the difference of survival rate between the two groups, and further analyzed the correlation between ADC and survival rate.ResultsCompared with the control group, the tumor size in the objective response group was significantly reduced (3.32±1.60 vs. 5.07±2.19 cm, P=0.000); ADC significantly increased (1.23±0.18 vs. 0.98±0.18 ×10-3 mm2/s, P=0.000); albumin significantly increased (39.32±4.14 vs. 37.46±4.18 g/L, P=0.016); the proportion of patients with poorly differentiated or undifferentiated tumor cells was significantly lower (51.25% vs. 72.92%, P=0.016); and the 5-year mortality decreased significantly (40.00% vs. 58.33%, P=0.044). ADC had the highest predictive value of objective response for locally advanced CRC patients after neoadjuvant chemotherapy, and the area under the curve (AUC) was 0.834 [95% confidence interval (CI): 0.765-0.903, P=0.000]; ADC had certain predictive value for the 5-year survival of locally advanced CRC patients, and the AUC was 0.778 (95% CI: 0.696-0.861, P=0.000). ADC >1.055×10-3 mm2/s, tumor size <4.1 cm, and moderately or well differentiated tumors were favorable factors for patients with locally advanced CRC to obtain objective response after neoadjuvant chemotherapy (P<0.05).ConclusionsADC could be used as a predictor of the efficacy of neoadjuvant chemotherapy in locally advanced CRC patients.

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In vivo assessment of optimal b-value range for perfusion-insensitive apparent diffusion coefficient imaging.

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