Rationale and Objectives
The aim of this study was to evaluate differences in tumor depiction and measured tumor apparent diffusion coefficient (ADC) with the use of a high-resolution diffusion-weighted (DW) magnetic resonance imaging (MRI) sequence, compared to a standard DW MRI sequence, in patients with locally advanced breast cancer.
Materials and Methods
Patients with locally advanced breast cancer were scanned with a reduced–field of view (rFOV) DW MRI sequence (high resolution) and a standard–field of view diffusion sequence (standard resolution), and differences between the two sequences were evaluated quantitatively (by calculating tumor ADC distribution parameters) and qualitatively (by radiologists’ visual assessments of images).
Results
Although the mean tumor ADC for both sequences was similar, differences were found in other parameters, including the 12.5th percentile ( P = .042) and minimum tumor ADC ( P = .003). Qualitatively, visualization of tumor morphologic detail, heterogeneity, and conspicuity was improved with rFOV DW MRI, and image quality was higher.
Conclusions
Differences in ADC distribution parameters and qualitative image features suggest that the sequences differ in their ability to capture tumor heterogeneity. These differences are not apparent when the mean is used to evaluate tumor ADC. In particular, differences found in lower ADC values are compatible with reduced partial voluming in rFOV DW MRI, suggesting that rFOV DW MRI may be valuable in imaging the lower ADCs expected to correspond to viable tumor in most invasive breast cancers.
Diffusion-weighted (DW) magnetic resonance imaging (MRI) provides a noninvasive, noncontrast, three-dimensional method to measure the random motion of water molecules, quantified as the apparent diffusion coefficient (ADC), in vivo. DW MRI is a promising tool for characterizing microstructural properties of breast lesions, with applications to both diagnostic and prognostic studies. Decreased ADC has been reported in malignant tumors relative to normal breast tissue . In patients with locally advanced breast cancer, DW MRI has been shown to have value in predicting response to neoadjuvant chemotherapy .
Despite this promise, DW MRI of the breast has yet to be fully integrated into clinical practice. Some prognostic studies have found little value in breast DW MRI in monitoring treatment response . Tumor response to treatment is likely to be heterogeneous, and high spatial resolution could improve the ability to capture heterogeneity in diffusivity. High-resolution DW MRI could improve prognostic and diagnostic applications in the breast, but obtaining higher resolution is technically challenging with current commercially available sequences. Most commercially available DW MRI sequences are echo-planar imaging (EPI) based, and spatial resolution is limited by the imaging field of view (FOV) and the number of phase and frequency encoding steps that can be acquired before the signal decays. Acquired in-plane resolution in DW MRI of the breast is generally 2 mm or worse. EPI sequences are also prone to distortion. In breast EPI, distortion and other artifacts are a particular problem, because of changes in magnetic susceptibility at the air-tissue interfaces at the anterior and lateral borders of both breasts, as well as in the adjacent lung.
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Materials and methods
Patients
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Imaging
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Contrast-enhanced imaging
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DW imaging
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Image Processing
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Image Analysis
Quantitative analysis
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Qualitative analysis
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Statistic Analysis
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Results
Patient Accrual and Tumor Characteristics
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Table 1
Characteristics of Tumors in rFOV DW MRI Study
Characteristic Number of Tumors Histopathologic subtype Invasive ductal carcinoma 10 (91%) Invasive lobular carcinoma 1 (9%) Tumor grade 1 0 2 8 (73%) 3 3 (27%) MRI tumor size MRI tumor volume (cm 3 ) 14.5 ± 16 (0.4–46.6) MRI longest diameter (cm) 4.4 ± 2.6 (1.3–9.3)
DW, diffusion-weighted; MRI, magnetic resonance imaging; rFOV, reduced–field of view.
Data are expressed as number (percentage) or as mean ± standard deviation (range).
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Quantitative Assessment of Tumor ADC Distributions
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Table 2
Comparison of ADC Distribution Parameters between rFOV and Standard-FOV DW MRI Acquisitions
Tumor ADC Variable rFOV Standard FOV Mean % Difference ∗ in rFOV Relative to Standard FOV_P_ Mean SD Mean SD Mean ADC 1094.8 120.1 1132.8 117.2 −2.83 .577 Skew 0.43 0.51 0.36 0.59 23.68 .638 Kurtosis 3.52 1.09 3.37 1.35 13.11 .320 Minimum ADC 231.18 269.0 603.73 306.62 −38.61 .003 12.5th-percentile ADC 749.59 169.1 870.18 192.65 −9.98 .042 25th-percentile ADC 877.50 139.9 962.4 150.52 −7.76 .083 50th-percentile ADC 1071.1 116.7 1102.6 118.29 −2.35 .638 75th-percentile ADC 1288.0 130.1 1295.5 100.92 −0.25 .765 87.5th-percentile ADC 1470.4 148.3 1451.2 93.25 1.65 .765 Maximum ADC 2149.7 272.6 1780.2 190.83 21.92 .002 ADC range 1918.5 446.2 1176.5 398.46 78.31 .001 Number of occupied bins 19.73 4.3 11.91 3.78 76.96 .001
ADC, apparent diffusion coefficient; DW, diffusion-weighted; FOV, field of view; MRI, magnetic resonance imaging; rFOV, reduced–field of view; SD, standard deviation. ADC and SD in units of 10 −6 mm 2 /s.
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![Figure 1, Bland-Altman plot of mean tumor apparent diffusion coefficient (ADC) calculated with reduced–field of view (rFOV) and standard-FOV diffusion-weighted (DW) magnetic resonance imaging (MRI). For each case, the average mean tumor ADC measure (1/2 × [mean ADC calculated from rFOV + mean ADC calculated from standard FOV]) is plotted against the difference between mean tumor ADC measures calculated from rFOV and standard-FOV DW MRI. Differences in measurements of mean ADC (×10 −6 mm 2s) are within 1.96 standard deviations (dotted lines) of the mean difference (dashed lines). The 95% confidence interval for the limits of agreement (dotted lines) is −207.38 × 10 −6 mm 2s to 283.26 × 10 −6 mm 2s.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/HighresolutionDiffusionweightedMagneticResonanceImaginginPatientswithLocallyAdvancedBreastCancer/0_1s20S1076633211005526.jpg)
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Qualitative Analysis
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Case Studies
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Discussion
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Conclusions
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