Rationale and Objectives
The aim of this study was to investigate the feasibility of applying measures sensitive to time-to-peak ( T peak ) heterogeneity as indicators for malignancy on breast dynamic contrast-enhanced magnetic resonance imaging.
Materials and Methods
The study included 39 benign and 97 malignant breast lesions from 103 patients. Lesions were automatically segmented by k-means clustering. Voxel-by-voxel T peak values were extracted using an empirical model. The p th percentile values ( p = 10, 20…) of the T peak distribution within each lesion and the fractional and absolute hot spot volumes were determined, where the hot spot volume is the volume of tissue with T peak less than a threshold value. Using the area under the receiver-operating characteristic curve (AUC), these measures were tested as indicators for differentiating fibroadenomas from invasive lesions and from ductal carcinoma in situ, as well as for differentiating nonfibroadenoma benign lesions from these malignant lesions. Region of interest–based T peak measurements were also tested. Finally, the relationship between hot spot volume and lesion volume was investigated.
Results
For differentiating fibroadenomas from malignant lesions, AUC values increased with decreasing values of p . At the optimal threshold (3 minutes), the hot spot volume provided high diagnostic performance (AUC ≥0.96 ± 0.02 for absolute hot spot volume). However, for differentiating nonfibroadenoma benign lesions from malignant lesions, AUC values were low. A significant correlation between absolute hot spot volume and lesion volume was found for malignant lesions and nonfibroadenoma benign lesions.
Conclusion
Quantitative analysis of the T peak distribution can be optimized for diagnostic performance, providing indicators sensitive to intralesion T peak heterogeneity.
Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) is used extensively for the diagnosis of breast lesions . Clinical DCE MRI analysis typically involves visual inspection of the time evolution of the signal enhancement and morphology of the enhanced region . However, there is growing interest in the development and assessment of quantitative methods to provide objective and improved diagnostic indicators .
Quantitative analysis applied to the time evolution (kinetics) of breast DCE MRI includes both empirical measures as well as pharmacokinetic models . Although the latter have the advantage of providing physiologic parameters, these models can be challenging to apply. There is ongoing research to deal with complex issues involved in their application, such as how to obtain accurate and robust arterial input functions as well as the level of model complexity and time resolution required . Empirical measures, on the other hand, are much simpler to apply. They can be applied to images that have been acquired in clinical scans using imaging parameters (eg., high spatial resolution, full breast coverage) that are preferred for radiologic assessment but may not be ideal for pharmacokinetic model analysis.
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Materials and methods
Patients and Lesions
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Table 1
Histopathologic Diagnoses for the 136 Breast Lesions
Diagnosis_n_Benign lesions 39 Fibroadenoma 23 Fibrosis 3 Fibrocystic change 3 Intraductal papilloma 2 Complex papillary lesion 3 Scar tissue 2 Skin lesion 1 Apocrine metaplasia 1 Fat necrosis 1Malignant lesions 97 Invasive ductal carcinoma 76 Ductal carcinoma in situ 12 Invasive lobular carcinoma 5 Invasive cancer with mucinous features 4All lesions 136
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Image Acquisition
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Whole-lesion Image Analysis
Lesion segmentation
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T peak analysis
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ΔS(t)=a∗t∗exp(−tc/b), Δ
S
(
t
)
=
a
∗
t
∗
exp
(
−
t
c
/
b
)
,
ΔS(t)=S(t)−S0, Δ
S
(
t
)
=
S
(
t
)
−
S
0
,
where t is the time elapsed after the beginning of contrast agent administration; S ( t ) is signal intensity at time t ; S 0 is signal intensity before contrast agent administration; and a , b , and c are free parameters that can vary from voxel to voxel. The trust-region algorithm was applied for nonlinear curve fitting. The T peak of each curve was calculated using the following relationship :
Tpeak=(b/c)1c. T
peak
=
(
b
/
c
)
1
c
.
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ROI Image Analysis
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Receiver-operating Characteristic (ROC) Analysis
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Results
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Table 2
AUC Values for Five Measures in Differentiating Four Groups of Breast Lesions
Comparison AUC ± Standard Error Manual ROI 10th Percentile 50th Percentile Fractional (3 minutes) Absolute (3 minutes) Fibroadenoma vs invasive 0.87 ± 0.05 c 0.93 ± 0.03 a,b 0.88 ± 0.03 b,c 0.95 ± 0.02 a 0.96 ± 0.02 a Fibroadenoma vs DCIS 0.94 ± 0.04 a,b 0.87 ± 0.06 b 0.63 ± 0.11 c 0.94 ± 0.04 a,b 0.99 ± 0.01 a Nonfibroadenoma benign vs invasive 0.58 ± 0.09 c 0.66 ± 0.09 c 0.66 ± 0.09 c 0.67 ± 0.08 c 0.72 ± 0.08 c Nonfibroadenoma benign vs DCIS 0.63 ± 0.11 c 0.52 ± 0.11 c 0.41 ± 0.11 c 0.53 ± 0.11 c 0.71 ± 0.10 c
Absolute, absolute hot spot volume; AUC, area under the receiver-operating characteristic curve; DCIS, ductal carcinoma in situ; Fractional, fractional hot spot volume; ROI, region of interest.
In the same row, measures with different subscript letters are significantly different (receiver-operating characteristic comparison test, P < .05), and measures with the same subscript letters are not significantly different (receiver-operating characteristic comparison test, P ≥ .05).
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Table 3
Linear Regression Analysis for Absolute Hot Spot Volume at a Threshold of 3 Minutes Versus Lesion Volume
Lesion Coefficient_F_ Statistics Slope Intercept (mm 3 )R 2 F__P Nonfibroadenoma benign 0.17 ± 0.08 400 ± 900 0.26 4.9 .04 Ductal carcinoma in situ 0.09 ± 0.03 500 ± 700 0.53 11 .007 Invasive 0.27 ± 0.02 50 ± 400 0.74 243 <.001
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Discussion
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Conclusions
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Appendix
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C(t)=D⋅Ktrans⋅∑2i=1ai⋅e−kep⋅t−e−mi⋅tmi−kep, C
(
t
)
=
D
⋅
K
trans
⋅
∑
i
=
1
2
a
i
⋅
e
−
k
ep
⋅
t
−
e
−
m
i
⋅
t
m
i
−
k
ep
,
where D is the dose of contrast agent (gadopentetate dimeglumine) normalized by body weight (millimoles per kilogram), K trans is the endothelial transfer constant for transporting contrast agent from plasma to interstitial space, and k ep is the rate constant for transport from interstitial space to plasma. Also, a i and m i are the amplitudes and rate constants describing the two exponential components of the arterial input function.
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0=∑2i=1ai⋅mi⋅e−mi⋅Tpeak−kep⋅e−kep⋅Tpeakmi−kep. 0
=
∑
i
=
1
2
a
i
⋅
m
i
⋅
e
−
m
i
⋅
T
peak
−
k
ep
⋅
e
−
k
ep
⋅
T
peak
m
i
−
k
ep
.
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