Correlation between histology-derived and ISODATA-derived non-viable tumor fractions.

<p>Correlation plots of ISODATA-derived non-viable tumor fractions following segmentation with feature vectors {ADC}, {T₂, ADC} and {T₁, T₂, ADC} as a function of the histology-derived non-viable tumor fractions for two different groups of animals: ‘1 h after HIFU + Control’ (<b>A</b>) and ‘72 h after HIFU + Control’ (<b>B</b>). The symbols ○, □ and ▴indicate groups ‘1 h after HIFU’, ‘72 h after HIFU’ and ‘Control’, respectively. Correlation values between the ISODATA-derived and the histology-derived tumor fractions are listed in the top left corner of each plot.</p

One-to-one correspondence between histology-derived and ISODATA-derived non-viable tumor fractions.

<p>Scatter plots of the ISODATA-derived non-viable tumor fractions following segmentation with feature vectors {ADC}, {T₂, ADC} and {T₁, T₂, ADC} as a function of the histology-derived non-viable tumor fractions. The symbols ○, □ and ▴ indicate groups ‘1 h after HIFU’, ‘72 h after HIFU’ and ‘Control’, respectively. The line of identity is shown as visual reference. The R² values of the data to the line of identity are shown in the top left corner of each plot.</p

R² values of ISODATA-derived versus histology-derived non-viable tumor fractions to the line of identity for all assessed feature vectors.

<p>R² values of ISODATA-derived versus histology-derived non-viable tumor fractions to the line of identity for all assessed feature vectors.</p

Multiparametric MRI Analysis for the Identification of High Intensity Focused Ultrasound-Treated Tumor Tissue

<div><p>Purpose</p><p>In this study endogenous magnetic resonance imaging (MRI) biomarkers for accurate segmentation of High Intensity Focused Ultrasound (HIFU)-treated tumor tissue and residual or recurring non-treated tumor tissue were identified.</p><p>Methods</p><p>Multiparametric MRI, consisting of quantitative T₁, T₂, Apparent Diffusion Coefficient (ADC) and Magnetization Transfer Ratio (MTR) mapping, was performed in tumor-bearing mice before (n = 14), 1 h after (n = 14) and 72 h (n = 7) after HIFU treatment. A non-treated control group was included (n = 7). Cluster analysis using the Iterative Self Organizing Data Analysis (ISODATA) technique was performed on subsets of MRI parameters (feature vectors). The clusters resulting from the ISODATA segmentation were divided into a viable and non-viable class based on the fraction of pixels assigned to the clusters at the different experimental time points. ISODATA-derived non-viable tumor fractions were quantitatively compared to histology-derived non-viable tumor volume fractions.</p><p>Results</p><p>The highest agreement between the ISODATA-derived and histology-derived non-viable tumor fractions was observed for feature vector {T₁, T₂, ADC}. R₁ (1/T₁), R₂ (1/T₂), ADC and MTR each were significantly increased in the ISODATA-defined non-viable tumor tissue at 1 h after HIFU treatment compared to viable, non-treated tumor tissue. R₁, ADC and MTR were also significantly increased at 72 h after HIFU.</p><p>Conclusions</p><p>This study demonstrates that non-viable, HIFU-treated tumor tissue can be distinguished from viable, non-treated tumor tissue using multiparametric MRI analysis. Clinical application of the presented methodology may allow for automated, accurate and objective evaluation of HIFU treatment.</p></div

Mean MRI parameter values in ISODATA-defined viable and non-viable tumor tissue.

<p>MRI parameter values (mean±SD) in viable tumor tissue (tumor tissue assigned as viable tumor tissue at all time points (n = 14)), non-viable tumor tissue at 1 h after HIFU (n = 14) and non-viable tumor tissue at 72 h after HIFU (n = 7) of the HIFU-treated animals following ISODATA segmentation with feature vector {T₁, T₂, ADC}. * and ** denote a significant difference between viable and non-viable tumor tissue with p<0.05 and p<0.001, respectively (paired Student's t-test).</p

MRI parameter maps before and longitudinally after HIFU treatment.

<p>Representative example of multiparametric MRI of the hind limb region of a HIFU-treated tumor-bearing mouse before and 1 h and 72 h after HIFU treatment. T₂-weighted images of an axial slice of the tumor-bearing paw are shown in the left panel. The hyper-intense tumor tissue is surrounded by hypo-intense muscle tissue. In the other panels the same T₂-weighted images are displayed except that the tumor pixels are overlaid with MRI parameter maps. The parameter maps were scaled according to the color scale bar shown at the right-hand side of the figure. The corresponding parameter range for this scale bar is indicated above each panel. The approximate direction of the HIFU treatment is shown by the white arrow on the T₂-weighted image, which was collected 1 h after HIFU treatment.</p

Visual correspondence between ISODATA-derived and histology-derived non-viable tumor areas.

<p><b>A</b>) Representative T₂-weighted images of the hind limb region of two HIFU-treated mice before, 1 h after and 72 h after HIFU. The results of ISODATA segmentation with feature vector {T₁, T₂, ADC} are overlaid on the tumor pixels. NADH-diaphorase stained sections of tumors dissected at 72 h after HIFU were made at approximately the same location within the tumor and are shown at the bottom of each column. ROIs around the entire (black line) and non-viable (red line) tumor tissue were drawn manually. Data in the left column are from the animal presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099936#pone-0099936-g001" target="_blank">Figure 1</a>. <b>B</b>) Similar data of a non-treated control mouse that was subjected to serial MRI measurements at the same time points (Day 0, Day 1 and Day 4) as the HIFU-treated animals. Scale bar = 1 mm.</p

Average tumor values of DCE-MRI derived parameters at different time points before and after PDT, for treated and non-treated animals.

<p>Based on independent <i>t</i>-tests, average non-enhanced tumor fractions were significantly different between treated and non-treated animals right after, and 24 and 72 h after PDT (all: <i>p</i> < 0.0005). For all time points after PDT, the repeated measurements difference of treated animals compared to before PDT was significant (all: <i>p</i> < 0.0005), while this was not the case for controls. Directly after PDT, the average tumor K^trans decreased and v_e increased significantly compared to baseline based on repeated measures (both: <i>p</i> < 0.0001), and also compared to untreated animals at the same time point (<i>p</i> < 0.0001 and <i>p</i> = 0.038, respectively).</p

Mean R₁, R₂, and ADC values of tumors of non-treated mice and treated mice.

<p>At 24 h, ADC values were significantly different for treated versus control mice (independent <i>t</i>-test, <i>p</i> = 0.002) as well as for treated versus baseline (paired <i>t</i>-test, <i>p</i> = 0.003). At 72 h, all parameters were significantly increased, compared to control animals at the same time point (independent <i>t</i>-test, <i>p</i> = 0.009 for R₁, <i>p</i> = 0.010 for R₂, <i>p</i> < 0.001 for ADC) as well as compared to baseline values (paired <i>t</i>-test, <i>p</i> = 0.019 for R₁, <i>p</i> = 0.027 for R₂, and <i>p</i> < 0.001 for ADC).</p

Representative examples of maps of endogenous MR parameters of two mice.

<p>First, second, and third columns show measurements of a single mouse obtained before, right after, and 24 h after PDT, respectively. The other three columns contain data acquired before, right after, and at 72 h post PDT of another mouse. The upper row contains T₂-weighted anatomical reference images, which were used for tumor segmentation, indicated by the red contours. Rows 2 to 4 show R₁ maps, R₂ maps, and ADC maps, respectively. The color bar corresponds to the range of values indicated on the left.</p