Diffusion-weighted imaging of a prostate cancer xenograft model seen on a 7 Tesla animal MR scanner: comparison of ADC values and pathologic findings

Microvascular proliferation is associated with high tumour blood flow by mpMRI and disease progression in primary prostate cancer

Active angiogenesis may be assessed by immunohistochemistry using Nestin, a marker of newly formed vessels, combined with Ki67 for proliferating cells. Here, we studied microvascular proliferation by Nestin-Ki67 co-expression in prostate cancer, focusing on relations to quantitative imaging parameters from anatomically matched areas obtained by preoperative mpMRI, clinico-pathological features and prognosis. Tumour slides from 67 patients (radical prostatectomies) were stained for Nestin-Ki67. Proliferative microvessel density (pMVD) and presence of glomeruloid microvascular proliferation (GMP) were recorded. From mpMRI, forward volume transfer constant (Ktrans), reverse volume transfer constant (kep), volume of EES (ve), blood flow, and apparent diffusion coefficient (ADC) were obtained. High pMVD was associated with high blood flow (p = 0.008) and low ADC (p = 0.032). High Ktrans, kep, and blood flow were associated with high Gleason score. High pMVD, GMP, and low ADC were associated with most adverse clinico-pathological factors. Regarding prognosis, high pMVD, Ktrans, kep, and low ADC were associated with reduced biochemical recurrence-free- and metastasis-free survival (p ≤ 0.044) and high blood flow with reduced time to biochemical- and clinical recurrence (p < 0.026). In multivariate analyses however, microvascular proliferation was a stronger predictor compared with blood flow. Indirect, dynamic markers of angiogenesis from mpMRI and direct, static markers of angiogenesis from immunohistochemistry may aid in the stratification and therapy planning of prostate cancer patients.

Signaling new therapeutic opportunities: cytokines in prostate cancer

INTRODUCTION

Despite FDA approval of sipuleucel-T in 2010, endeavors to use immune checkpoint inhibitors in unselected prostate cancer patients have not improved clinical outcomes. These efforts include studies with anti-PD1/PD-L1 and anti-CTLA-4 alone and in combination with existing standards of care. These strategies are generally T-cell centric and disregard the broader complex and pleiotropic components of the prostate cancer tumor microenvironment such as natural killer cells, myeloid-derived suppressor cells and tumor associated macrophages.

AREAS COVERED

We performed an online literature search and undertook a review of existing pre-clinical and clinical literature for cytokine-based therapy relating to prostate cancer, specifically on interleukin (IL)-2, IL-15, IL-12, IL-23, IL-8 and transforming growth factor (TGF)-β.

EXPERT OPINION

Cytokine-based therapies present an alternative immune strategy to target the pleiotropic prostate cancer tumor microenvironment beyond T-cells. Future immunotherapy strategies in prostate cancer should address these immune cell populations which may play more important roles in the prostate cancer tumor microenvironment.

Intravoxel Incoherent Motion Diffusion-Weighted Imaging for Predicting and Monitoring the Response of Anti-Angiogenic Treatment in the Orthotopic Nude Mouse Model of Lung Adenocarcinoma

BACKGROUND

The treatment efficacy of angiogenesis inhibitor could be underestimated at an early stage based on tumor volume changes. Intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) can quantitatively assess tumors at the cellular level, but it is unclear whether it can provide useful information for assessing treatment response of anti-angiogenic treatment for lung adenocarcinoma.

PURPOSE

To determine the use of IVIM-DWI for non-invasive monitoring of the early response to anti-angiogenic treatment in the orthotopic transplantation of lung adenocarcinoma model.

STUDY TYPE

Prospective.

POPULATION

Thirty-seven nude mice were randomized into two groups: treatment group (received bevacizumab + cisplatin, N = 20) and control group (received saline, N = 17).

FIELD STRENGTH/SEQUENCE

Single-shot turbo spin-echo (TSE) IVIM-DWI, TSE T2-weighted imaging at 3.0 T.

ASSESSMENT

Tumor volume, IVIM parameters (apparent diffusion coefficient [ADC], diffusivity [D], perfusion fraction [f], and pseudo-diffusion coefficient [D*]) were measured before and 2 hours, 3, 7, 10 and 14 days after treatment. Regions of interest were manually drawn along the inner edge of the tumor by two radiologists with 5 and 10-year experience in magnetic resonance imaging. Pathological examinations (hematoxylin and eosin stain, cluster of differentiation 34) were performed.

STATISTICAL TESTS

Kolmogorov-Smirnov test, repeated-measure two-way analysis of variance test, Mann-Whitney U test, Pearson correlation analysis, receiver operating characteristic curve. P < 0.05 was considered statistically significant.

RESULTS

The tumor volume of the two groups was significantly different only on day 14 (control group vs. treatment group, 43.15 ± 18.28 mm³ vs. 28.41 ± 1.71 mm³ ). ADC_2h , ADC_10d , D_2h , D_7d , D_10d , and D_14d were significantly higher, while f_10d and f_14d were significantly lower in the treatment group compared to those of the control group. Both the △ADC_2h (r = -0.631) and △D_2h (r = -0.700) showed moderate correlations with the relative tumor volume on day 14.

DATA CONCLUSION

IVIM has the potential to predict and monitor the early response to anti-angiogenic treatment, earlier than size changes, for lung adenocarcinoma.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 4.

Association Between VEGF Expression and Diffusion Weighted Imaging in Several Tumors-A Systematic Review and Meta-Analysis

To date, only a few studies have investigated relationships between Diffusion-weighted imaging (DWI) and Vascular endothelial growth factor (VEGF) expression in tumors. The reported results are contradictory. The aim of the present analysis was to review the published results and to perform a meta-analysis regarding associations between apparent diffusion coefficients (ADC) derived from DWI and VEGF expression. MEDLINE library was screened for relationships between ADC and VEGF expression up to January 2019. Overall, 14 studies with 578 patients were identified. In 10 studies (71.4%) 3 T scanners were used and in four studies (28.6%) 1.5 T scanners. Furthermore, seven studies (50%) had a prospective design and seven studies (50%) had a retrospective design. Most frequently, prostate cancer, followed by rectal cancer, cervical cancer and esophageal cancer were identified. The pooled correlation coefficient of all tumors was r = -0.02 [95% CI -0.26-0.21]. ADC values derived from routinely acquired DWI do not correlate with VEGF expression in various tumors. Therefore, DWI is not sensitive enough to reflect angiogenesis-related microstructure of tumors.

Study of diffusion-weighted magnetic resonance imaging in the evaluation of the response to AAV2-VEGF-Trap neoadjuvant treatment in a triple-negative breast cancer animal model

Objective

Evaluation of the efficacy of adeno‐associated virus 2 mediated gene transfer of vascular endothelial growth factor Trap (AAV2‐VEGF‐Trap) alone or combination with paclitaxel in a mouse model of triple‐negative breast cancer (TNBC) using diffusion‐weighted magnetic resonance imaging (DW‐MRI) and in vivo fluorescence imaging.

Materials and Methods

Xenografted TNBC tumors were established by subcutaneous injection of MDA‐MB‐231 cells into nude mice. Tumors were treated with AAV2‐VEGF‐Trap, paclitaxel, AAV2‐VEGF‐Trap combined with paclitaxel and control. A 7.0‐Tesla magnetic resonance (MR) was used to obtain the apparent diffusion coefficient (ADC) values and ΔADC values. In vivo fluorescence imaging coupled with the optical imaging probe AngioSense680 EX was acquired to obtain average luminous intensity values. Immunohistochemical staining of tumor Ki‐67 and vascular endothelial cell marker antigen (CD31) were used to evaluate the effects on tumor proliferation and angiogenesis.

Results

The combination of AAV2‐VEGF‐Trap with paclitaxel exhibited greater tumor growth inhibition compared with the other groups. The ADC values in the paclitaxel group and the AAV2‐VEGF‐Trap in combination with paclitaxel group were significant greater compared with the control group, and the ΔADC values of all treatment groups were significantly increased compared with the control group on the 14th day after administration. Decreased microvessel density and luminous intensity in the treatment groups that contain AAV2‐VEGF‐Trap were observed. Reduced proliferation activity was noted in groups that contained paclitaxel.

Conclusion

AAV2‐VEGF‐Trap inhibits TNBC growth though inhibiting tumor neovascularization with a single intravenous injection, and AAV2‐VEGF‐Trap exhibits a synergistic effect when used in combination with paclitaxel for TNBC neoadjuvant therapy. In vivo fluorescence imaging can detect the anti‐angiogenesis effect of AAV2‐VEGF‐Trap early and noninvasively. DW‐MRI can longitudinally monitor the neoadjuvant efficacy of TNBC.

Diffusion-weighted MRI in solitary pulmonary lesions: associations between apparent diffusion coefficient and multiple histopathological parameters

Apparent diffusion coefficient (ADC) from diffusion-weighted imaging (DWI) has gained wide attention as potential tool for differentiating between malignant and benign solitary pulmonary lesions (SPLs). The overall effects of multiple histopathological parameters on ADC have not been elucidated, which may help to explain the overlapping of ADC between malignant and benign SPLs. The study sought to explore associations between ADC and histopathological parameters in SPLs, and to compare diagnostic capability of ADC among different types of SPLs. Multiple histopathological parameters (cell density, nuclear-to-cytoplasm ratio, necrotic fraction, presence of mucus and grade of differentiation) were quantified in 52 malignant and 13 benign SPLs with surgical pathology available. Cell density (β = −0.40) and presence of mucus (β = 0.77) were independently correlated with ADC in malignant SPLs. The accurate diagnosis rate of squamous carcinomas, adenocarcinomas without mucus and malignant tumors with mucus was 100%, 82% and 0%, respectively. Our study suggested that cell density and presence of mucus are independently correlated with ADC in malignant SPLs. Squamous carcinoma maybe more accurately diagnosed as malignancy by ADC value. Malignant SPLs with mucus and adenocarcinomas with low cell density should be kept in mind in differentiating SPLs using ADC because of insufficient diagnostic capability.

Apparent diffusion coefficients in prostate cancer: correlation with molecular markers Ki-67, HIF-1α and VEGF

Prostate cancer (PCa) is the second most common cancer in men. The Gleason score (GS) and biomarkers play important roles in the diagnosis and treatment of patients with PCa. The purpose of this study was to investigate the relationship between the apparent diffusion coefficient (ADC) and the molecular markers Ki-67, hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) in PCa. Thirty-nine patients with 39 lesions, who had been diagnosed with PCa, were enrolled in this study. All patients underwent diffusion-weighted magnetic resonance imaging (DW-MRI) (b = 800 s/mm² ). The expression of Ki-67, HIF-1α and VEGF was assessed by immunohistochemistry. Statistical analysis was applied to analyze the association between ADC and prostate-specific antigen (PSA), GS and the expression of Ki-67, HIF-1α and VEGF. The group differences in ADC among different grades of Ki-67, HIF-1α and VEGF were also analyzed. The mean ± standard deviation of ADC was (0.76 ± 0.27) × 10^-3  mm² /s. ADC correlated negatively with PSA and GS (p < 0.05). The Ki-67 staining index (SI), HIF-1α expression and VEGF expression in PCa were correlated inversely with ADC, controlling for age (r = -0.332, p < 0.05; r = -0.662, p < 0.0005; and r = -0.714, p < 0.0005, respectively). ADC showed a significant difference among different grades of Ki-67 (F = 9.164, p = 0.005), HIF-1α (F = 40.333, p < 0.0005) and VEGF (F = 22.048, p < 0.0005). In conclusion, ADC was correlated with PSA, GS, and Ki-67, HIF-1α and VEGF expression in patients with PCa. ADC may be used to evaluate tumor proliferation, hypoxia and angiogenesis in PCa.

The impact of computed high b-value images on the diagnostic accuracy of DWI for prostate cancer: A receiver operating characteristics analysis

To evaluate the performance of computed high b value diffusion-weighted images (DWI) in prostate cancer detection. 97 consecutive patients who had undergone multiparametric MRI of the prostate followed by biopsy were reviewed. Five radiologists independently scored 138 lesions on native high b-value images (b = 1200 s/mm²), apparent diffusion coefficient (ADC) maps, and computed high b-value images (contrast equivalent to b = 2000 s/mm²) to compare their diagnostic accuracy. Receiver operating characteristic (ROC) analysis and McNemar’s test were performed to assess the relative performance of computed high b value DWI, native high b-value DWI and ADC maps. No significant difference existed in the area under the curve (AUC) for ROCs comparing B1200 (b = 1200 s/mm²) to computed B2000 (c-B2000) in 5 readers. In 4 of 5 readers c-B2000 had significantly increased sensitivity and/or decreased specificity compared to B1200 (McNemar’s p < 0.05), at selected thresholds of interpretation. ADC maps were less accurate than B1200 or c-B2000 for 2 of 5 readers (P < 0.05). This study detected no consistent improvement in overall diagnostic accuracy using c-B2000, compared with B1200 images. Readers detected more cancer with c-B2000 images (increased sensitivity) but also more false positive findings (decreased specificity).

[68Ga]pentixafor for CXCR4 imaging in a PC-3 prostate cancer xenograft model - comparison with [18F]FDG PET/CT, MRI and ex vivo receptor expression

Purpose

The aim was to characterize the properties of [⁶⁸Ga]Pentixafor as tracer for prostate cancer imaging in a PC-3 prostate cancer xenograft mouse model and to investigate its correlation with [¹⁸F]FDG PET/CT, magnetic resonance imaging (MRI) and ex vivo analyses.

Methods

Static [⁶⁸Ga]Pentixafor and [¹⁸F]FDG PET as well as morphological/ diffusion weighted MRI and ¹H MR spectroscopy was performed. Imaging data were correlated with ex vivo biodistribution and CXCR4 expression in PC-3 tumors (immunohistochemistry (IHC), mRNA analysis). Flow cytometry was performed for evaluation of localization of CXCR4 receptors (in vitro PC-3 cell experiments).

Results

Tumor uptake of [⁶⁸Ga]Pentixafor was significantly lower compared to [¹⁸F]FDG. Ex vivo CXCR4 mRNA expression of tumors was shown by PCR. Only faint tumor CXCR4 expression was shown by IHC (immuno reactive score of 3). Accordingly, flow cytometry of PC-3 cells revealed only a faint signal, cell membrane permeabilisation showed a slight signal increase. There was no significant correlation of [⁶⁸Ga]Pentixafor tumor uptake and ex vivo receptor expression. Spectroscopy showed typical spectra of prostate cancer.

Conclusion

PC-3 tumor uptake of [⁶⁸Ga]Pentixafor was existent but lower compared to [¹⁸F]FDG. No significant correlation of ex vivo tumor CXCR4 receptor expression and [⁶⁸Ga]Pentixafor tumor uptake was shown. CXCR4 receptor expression on the surface of PC-3 cells was existent but rather low possibly explaining the limited [⁶⁸Ga]Pentixafor tumor uptake; receptor localization in the interior of PC-3 cells is presumable as shown by cell membrane permeabilisation. Further studies are necessary to define the role of [⁶⁸Ga]Pentixafor in prostate cancer imaging.

Application of in vivo imaging techniques to monitor therapeutic efficiency of PLX4720 in an experimental model of microsatellite instable colorectal cancer

OBJECTIVES

Patient-derived tumor cell lines are a powerful tool to analyze the sensitivity of individual tumors to specific therapies in mice. An essential prerequisite for such an approach are reliable quantitative techniques to monitor tumor progression in vivo.

METHODS

We have employed HROC24 cells, grown heterotopically in NMRI Foxn1^nu mice, as a model of microsatellite instable colorectal cancer to investigate the therapeutic efficiencies of 5'-fluorouracil (5'-FU) and the mutant BRAF inhibitor PLX4720, a vemurafenib analogue, by three independent methods: external measurement by caliper, magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-(¹⁸F)fluoro-D-glucose (¹⁸F-FDG).

RESULTS

Repeated measure ANOVA by a general linear model revealed that time-dependent changes of anatomic tumor volumes measured by MRI differed significantly from those of anatomic volumes assessed by caliper and metabolic volumes determined by PET/CT. Over the investigation period of three weeks, neither 5'-FU, PLX4720 nor a combination of both drugs affected the tumor volumes. Also, there was no drug effect on the apparent diffusion constant (ADC) value as detected by MRI. Interestingly, however, PET/CT imaging showed that PLX4720-containing therapies transiently reduced the standardized uptake value (SUV), indicating a temporary response to treatment.

CONCLUSIONS

5'-FU and PLX4720 were largely ineffective with respect to HROC24 tumor growth. Tumoral uptake of ¹⁸F-FDG, as expressed by the SUV, proved as a sensitive indicator of small therapeutic effects. Metabolic imaging by ¹⁸F-FDG PET/CT is a suitable approach to detect effects of tumor-directed therapies early and even in the absence of morphological changes.

Evaluation of the efficacy of chemoradiotherapy in cervical cancer using diffusion-weighted imaging and apparent diffusion coefficient

Objective

This study aims to evaluate the efficacy of chemoradiotherapy (CRT) in cervical cancer using diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) values.

Methods

A total of 71 patients with cervical cancer were enrolled in this study. All patients underwent conventional magnetic resonance imaging and DWI scanning before CRT and at 7, 14, 21 days, and 6 months after CRT. These patients were divided into the complete response (CR) and non-CR groups according to the response evaluation criteria in solid tumors criteria. Receiver operating characteristic (ROC) curve was used to evaluate the accuracy of ADC values in predicting the efficacy of CRT in cervical cancer.

Results

Compared with before-CRT treatment, tumor volumes were reduced and ADC values were elevated in both CR and non-CR groups after CRT treatment. At 21 days after CRT, tumor volumes in the CR group were smaller than those in the non-CR group. During the period of 21 days to 6 months after CRT, tumor regression rate and the increased rate of ADC values in the CR group were higher than those in the non-CR group. ROC curves revealed that the increased rate of ADC values at 21 days after CRT was the optimal time point for the prediction of CRT efficacy in cervical cancer, with the area under the curve, sensitivity, and specificity of 0.775, 92.7%, and 62.5%, respectively.

Conclusion

Our study provides evidence that the increased rate of ADC at 21 days after CRT might be a promising tool for predicting the efficacy of CRT in cervical cancer.

Enhanced binding of necrosis-targeting immunocytokine NHS-IL12 after local tumour irradiation in murine xenograft models

PURPOSE

NHS-IL12 is an immunocytokine targeting necrotic tumour areas. IL12 shows anti-tumour activity. As local irradiation might induce additional necrosis in solid tumours, we aimed to evaluate the increase in intratumoural accumulation of NHS-IL12 after irradiation and correlate the findings with diffusion-weighted MRI studies in two xenograft models.

METHODS

Human rhabdomyosarcoma (A204) and prostate cancer (PC3) cells were studied in vitro and as subcutaneous xenografts. Radiation sensitivity of the cell lines was assessed in vitro by colony formation assays. In vivo tumour necrosis was assessed based on apparent diffusion coefficients (ADC). Biodistribution of NHS-IL12 was evaluated with and without tumour irradiation using in vivo small-animal PET and ex vivo biodistribution.

RESULTS

A204 and PC3 differed in their intrinsic radiation sensitivity. Accordingly, radiation-induced tumour necrosis was found only in A204 xenografts. In comparison with control, ADC was significantly increased after irradiation of A204 tumours with 1 × 8.0 Gy and 5 × 2.0 Gy, whereas no change in ADC was observed in PC3 xenografts in all irradiation regimes. ADC correlated with histology. An enhanced uptake of radiolabelled NHS-IL12 in A204 tumours was detected by PET and ex vivo biodistribution after tumour irradiation. In PC3 tumours, no increase in NHS-IL12 uptake was observed.

CONCLUSIONS

In dependence of the tumour model, tumour irradiation enhanced tumour necrosis measured in MRI and histology. In vivo PET and ex vivo biodistribution showed enhanced binding of NHS-IL12 in rhabdomyosarcoma xenografts. Thus, enhanced binding of necrosis-targeting immunocytokines might be a novel mechanism of additive effects in combination with irradiation.

The Correlation Between Diffusion-Weighted Imaging at 3.0-T Magnetic Resonance Imaging and Histopathology for Pancreatic Ductal Adenocarcinoma

PURPOSE

The aim of this study was to discuss the correlation between diffusion-weighted imaging (DWI) at 3.0-T magnetic resonance and histopathology for pancreatic ductal adenocarcinoma (PDA).

MATERIALS AND METHODS

Twenty-eight patients with histopathologically proven PDA were included in this study after 108 cases of suspected pancreatic tumors had been performed with DWI. The sequences of DWI included respiratory-triggered DWI and breath-hold DWI, which were performed with 2 b values (0 and 500 s/mm; 0 and 1000 s/mm), respectively. According to magnetic resonance images, wax blocks and slices were selected and stained with hematoxylin-eosin for anti-vascular endothelial growth factor (VEGF), anti-CD34, and anti-Ki-67 (Mib-1). The relationship between tumor apparent diffusion coefficient (ADC) and tumor fibrosis, as well as the expression of tumor VEGF, Ki-67, and multivessel density (MVD), were studied.

RESULTS

The ADC values of PDA of different grades of differentiation and fibrosis grade did not show statistically significant difference. The ADC values of PDA did not show the statistically significant correlation with the grades of differentiation, fibrosis grade, Ki-67 expression, and expression of VEGF and MVD.

CONCLUSIONS

The ADC of PDA cannot be used to reflect grades of differentiation, degree of tumor fibrosis, the expression of VEGF, the expression of Ki-67, and the tumor MVD.

Quantitative correlation at the molecular level of tumor response to docetaxel by multimodal diffusion-weighted magnetic resonance imaging and [¹⁸F]FDG/[¹⁸F]FLT positron emission tomography

We aimed to quantitatively characterize the treatment effects of docetaxel in the HCT116 xenograft mouse model, applying diffusion-weighted magnetic resonance imaging (MRI) and positron emission tomography (PET) using 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) and 3'-deoxy-3'-[¹⁸F]-fluorothymidine ([¹⁸F]FLT). Mice were imaged at four time points over 8 days. Docetaxel (15 mg/kg) was administered after a baseline scan. Voxel-wise scatterplots of PET and apparent diffusion coefficient (ADC) data of tumor volumes were evaluated with a threshold cluster analysis and compared to histology (GLUT1, GLUT3, Ki67, activated caspase 3a). Compared to the extensive tumor growth observed in the vehicle-treated group (from 0.32 ± 0.21 cm³ to 0.69 ± 0.40 cm³), the administration of docetaxel led to tumor growth stasis (from 0.32 ± 0.20 cm³ to 0.45 ± 0.23 cm³). The [¹⁸F]FDG/ADC cluster analysis and the evaluation of peak histogram values revealed a significant treatment effect matching histology as opposed to [¹⁸F]FLT/ADC. [¹⁸F]FLT uptake and the Ki67 index were not in good agreement. Our voxel-based cluster analysis uncovered treatment effects not seen in the separate inspection of PET and MRI data and may be used as an independent analysis tool. [¹⁸F]FLT/ADC cluster analysis could still point out the treatment effect; however, [¹⁸F]FDG/ADC reflected the histology findings in higher agreement.

Comparison of stretched-Exponential and monoexponential model diffusion-Weighted imaging in prostate cancer and normal tissues

BACKGROUND

To compare stretched-exponential and monoexponential model diffusion-weighted imaging (DWI) in prostate cancer and normal tissues.

METHODS

Twenty-seven patients with prostate cancer underwent DWI exam using b-values of 0, 500, 1000, and 2000 s/mm(2) . The distributed diffusion coefficients (DDC) and α values of prostate cancer and normal tissues were obtained with stretched-exponential model and apparent diffusion coefficient (ADC) values using monoexponential model. The ADC, DDC (both in 10(-3) mm(2)/s), and α values (range, 0-1) were compared among different prostate tissues. The ADC and DDC were also compared and correlated in each tissue, and the standardized differences between DDC and ADC were compared among different tissues.

RESULTS

Data were obtained for 31 cancers, 36 normal peripheral zone (PZ) and 26 normal central gland (CG) tissues. The ADC (0.71 ± 0.12), DDC (0.60 ± 0.18), and α value (0.64 ± 0.05) of tumor were all significantly lower than those of the normal PZ (1.41 ± 0.22, 1.47 ± 0.20, and 0.85 ± 0.09) and CG (1.25 ± 0.14, 1.32 ± 0.13, and 0.82 ± 0.06) (all P < 0.05). ADC was significantly higher than DDC in cancer, but lower than DDC in the PZ and CG (all P < 0.05). The ADC and DDC were strongly correlated (R(2)  = 0.99, 0.98, 0.99, respectively, all P < 0.05) in all the tissue, and standardized difference between ADC and DDC of cancer was slight but significantly higher than that in normal tissue.

CONCLUSION

The stretched-exponential model DWI provides more parameters for distinguishing prostate cancer and normal tissue and reveals slight differences between DDC and ADC values.

Intratumoral heterogeneity of breast cancer xenograft models: texture analysis of diffusion-weighted MR imaging

Objective

To investigate whether there is a relationship between texture analysis parameters of apparent diffusion coefficient (ADC) maps and histopathologic features of MCF-7 and MDA-MB-231 xenograft models.

Materials and Methods

MCF-7 estradiol (+), MCF-7 estradiol (-), and MDA-MB-231 xenograft models were made with approval of the animal care committee. Twelve tumors of MCF-7 estradiol (+), 9 tumors of MCF-7 estradiol (-), and 6 tumors in MDA-MB-231 were included. Diffusion-weighted MR images were obtained on a 9.4-T system. An analysis of the first and second order texture analysis of ADC maps was performed. The texture analysis parameters and histopathologic features were compared among these groups by the analysis of variance test. Correlations between texture parameters and histopathologic features were analyzed. We also evaluated the intraobserver agreement in assessing the texture parameters.

Results

MCF-7 estradiol (+) showed a higher standard deviation, maximum, skewness, and kurtosis of ADC values than MCF-7 estradiol (-) and MDA-MB-231 (p < 0.01 for all). The contrast of the MCF-7 groups was higher than that of the MDA-MB-231 (p = 0.004). The correlation (COR) of the texture analysis of MCF-7 groups was lower than that of MDA-MB-231 (p < 0.001). The histopathologic analysis showed that Ki-67_mean and Ki-67_diff of MCF-7 estradiol (+) were higher than that of MCF-7 estradiol (-) or MDA-MB-231 (p < 0.05). The microvessel density (MVD)_mean and MVD_diff of MDA-MB-231 were higher than those of MCF-7 groups (p < 0.001). A diffuse-multifocal necrosis was more frequently found in MDA-MB-231 (p < 0.001). The proportion of necrosis moderately correlated with the contrast (r = -0.438, p = 0.022) and strongly with COR (r = 0.540, p = 0.004). Standard deviation (r = 0.622, r = 0.437), skewness (r = 0.404, r = 0.484), and kurtosis (r = 0.408, r = 0.452) correlated with Ki-67_mean and Ki-67_diff (p < 0.05 for all). COR moderately correlated with Ki-67_diff (r = -0.388, p = 0.045). Skewness (r = -0.643, r = -0.464), kurtosis (r = -0.581, r = -0.389), contrast (r = -0.473, r = -0.549) and COR (r = 0.588, r = 0.580) correlated with MVD_mean and MVD_diff (p < 0.05 for all).

Conclusion

The texture analysis of ADC maps may help to determine the intratumoral spatial heterogeneity of necrosis patterns, amount of cellular proliferation and the vascularity in MCF-7 and MDA-MB-231 xenograft breast cancer models.

Potential of hybrid ¹⁸F-fluorocholine PET/MRI for prostate cancer imaging

PURPOSE

To report the first results of hybrid (18)F-fluorocholine PET/MRI imaging for the detection of prostate cancer.

METHODS

This analysis included 26 consecutive patients scheduled for prostate PET/MRI before radical prostatectomy. The examinations were performed on a hybrid whole-body PET/MRI scanner. The MR acquisitions which included T2-weighted, diffusion-weighted and dynamic contrast-enhanced sequences were followed during the same session by whole-body PET scans. Parametric maps were constructed to measure normalized T2-weighted intensity (nT2), apparent diffusion coefficient (ADC), volume transfer constant (K (trans)), extravascular extracellular volume fraction (v e) and standardized uptake values (SUV). With pathology as the gold standard, ROC curves were calculated using logistic regression for each parameter and for the best combination with and without PET to obtain a MR model versus a PETMR model.

RESULTS

Of the 26 patients initially selected, 3 were excluded due to absence of an endorectal coil (2 patients) or prosthesis artefacts (1 patient). In the whole prostate, the area under the curve (AUC) for SUVmax, ADC, nT2, K (trans) and v e were 0.762, 0.756, 0.685, 0.611 and 0.529 with a best threshold at 3.044 for SUVmax and 1.075 × 10(-3) mm(2)/s for ADC. The anatomical distinction between the transition zone and the peripheral zone showed the potential of the adjunctive use of PET. In the peripheral zone, the AUC of 0.893 for the PETMR model was significantly greater (p = 0.0402) than the AUC of 0.84 for the MR model only. In the whole prostate, no relevant correlation was observed between ADC and SUVmax. The SUVmax was not affected by the Gleason score.

CONCLUSION

The performance of a hybrid whole-body (18)F-fluorocholine PET/MRI scan in the same session combined with a prostatic MR examination did not interfere with the diagnostic accuracy of the MR sequences. The registration of the PET data and the T2 anatomical MR sequence data allowed precise localization of hypermetabolic foci in the prostate. While in the transition zone the adenomatous hyperplasia interfered with cancer detection by PET, the quantitative analysis tool performed well for cancer detection in the peripheral zone.

Tumor perfusion-related parameter of diffusion-weighted magnetic resonance imaging: correlation with histological microvessel density

PURPOSE

We obtained intravoxel incoherent motion (IVIM) parameters through biexponential analysis on diffusion-weighted MR imaging (DWI) using multiple b values. Correlation was evaluated between these parameters and histological microvessel density (MVD) for the possibility of noninvasive evaluation of MVD with DWI.

METHODS

Twenty-five nude mice with the HT29 colorectal cancer cells implanted were analyzed after undergoing DWI with multiple b values (0, 50, 100, 300, 500, 700, and 1000 s/mm(2)). Tissue diffusivity (D(t)), pseudo-diffusion coefficient (D(p)), and perfusion fraction (f(p)) were calculated using a biexponential analysis, and these parameters were correlated with MVD. The MVD was determined with the CD31 stain. For statistical analysis, Spearman's rank correlation was applied.

RESULTS

The mean value and correlation coefficient with MVD for each IVIM parameter were as follows: D(t)  = 0.98 ± 0.06 × 10(-3) mm(2)/s with r = 0.139 (P = 0.508); D(p) = 23.70 ± 7.94 × 10(-3) mm(2)/s with r = 0.782 (P < 0.001); and f(p) = 15.58 ± 5.7% with r = 0.749 (P < 0.001). D(p) and f(p) showed significant correlation with MVD, but D(t) did not.

CONCLUSION

The IVIM parameters, D(p) and f(p), on DWI might be used in the noninvasive evaluation of MVD.

Biexponential apparent diffusion coefficients values in the prostate: comparison among normal tissue, prostate cancer, benign prostatic hyperplasia and prostatitis

Objective

To investigate the biexponential apparent diffusion parameters of diverse prostate tissues and compare them with monoexponential apparent diffusion coefficient (ADC) value in the efficacy to discriminate prostate cancer from benign lesions.

Materials and Methods

Eleven healthy volunteers and 61 patients underwent a conventional (b-factors 0, 1000 s/mm²) and a 10 b-factor (0 to 3000 s/mm²) diffusion-weighted imaging (DWI). The monoexponential ADC value and biexponential parameters of fast ADC (ADCf), fraction of ADCf (f), slow ADC (ADCs) value for 29 prostate cancer, 28 benign prostatic hyperplasia (BPH), 24 prostatitis lesions and normal tissue were calculated and compared. Receiver operating characteristic analysis was performed to determine the sensitivity, specificity and optimal cut-off points.

Results

Prostate cancer had lower ADC, ADCf, f, and ADCs than all other tissues (p < 0.01). Prostatitis exhibited a lower ADC, ADCf, ADCs and f than the peripheral zone tissue (p < 0.01), and BPH showed a lower ADC and ADCf than the central gland tissue (p < 0.01). The ADCf demonstrated a comparable accuracy with ADC in differentiating cancer from BPH [area under the curve (AUC) 0.93 vs. 0.92] and prostatitis AUC 0.98 vs. 0.99) (both p > 0.05), but the AUC of f and ADCs in differentiating cancer from BPH (0.73 and 0.81) and prostatitis (0.88 and 0.91) were significantly lower than ADC (all p < 0.05).

Conclusion

The biexponential DWI appears to provide additional parameters for tissue characterization in prostate, and ADCf helps to yield comparable accuracy with ADC in differentiating cancer from benign lesions.