Magnetic resonance imaging of human melanoma xenografts in vivo: proton spin-lattice and spin-spin relaxation times versus fractional tumour water content and fraction of necrotic tumour tissue

T1 and T2 mapping for identifying malignant lymph nodes in head and neck squamous cell carcinoma

BACKGROUND

This study seeks to assess the utility of T1 and T2 mapping in distinguishing metastatic lymph nodes from reactive lymphadenopathy in patients with head and neck squamous cell carcinoma (HNSCC), using diffusion-weighted imaging (DWI) as a comparison.

METHODS

Between July 2017 and November 2019, 46 HNSCC patients underwent neck MRI inclusive of T1 and T2 mapping and DWI. Quantitative measurements derived from preoperative T1 and T2 mapping and DWI of metastatic and non-metastatic lymph nodes were compared using independent samples t-test or Mann-Whitney U test. Receiver operating characteristic curves and the DeLong test were employed to determine the most effective diagnostic methodology.

RESULTS

We examined a total of 122 lymph nodes, 45 (36.9%) of which were metastatic proven by pathology. Mean T2 values for metastatic lymph nodes were significantly lower than those for benign lymph nodes (p < 0.001). Conversely, metastatic lymph nodes exhibited significantly higher apparent diffusion coefficient (ADC) and standard deviation of T1 values (T1SD) (p < 0.001). T2 generated a significantly higher area under the curve (AUC) of 0.890 (0.826-0.954) compared to T1SD (0.711 [0.613-0.809]) and ADC (0.660 [0.562-0.758]) (p = 0.007 and p < 0.001). Combining T2, T1SD, ADC, and lymph node size achieved an AUC of 0.929 (0.875-0.983), which did not significantly enhance diagnostic performance over using T2 alone (p = 0.089).

CONCLUSIONS

The application of T1 and T2 mapping is feasible in differentiating metastatic from non-metastatic lymph nodes in HNSCC and can improve diagnostic efficacy compared to DWI.

Histogram analysis of quantitative parameters from synthetic MRI: correlations with prognostic factors in nasopharyngeal carcinoma

OBJECTIVES

To evaluate the correlation between histogram parameters derived from synthetic magnetic resonance imaging (SyMRI) and prognostically relevant factors in nasopharyngeal carcinoma (NPC).

METHODS

Fifty-nine consecutive NPC patients were prospectively enrolled. Quantitative parameters (T1, T2, and proton density (PD)) were obtained by outlining the three-dimensional volume of interest (VOI) of all lesions. Then, histogram analysis of these quantitative parameters was performed and the correlations with prognostically relevant factors were assessed. By choosing appropriate cutoff, we divided the sample into two groups. Independent-samples t test/Mann-Whitney U test was used and ROC curve analysis was further processed.

RESULTS

Histogram parameters of the T1, T2, and PD maps were positively correlated with the Ki-67 expression levels, and PD_mean was the most representative parameter (AUC: 0.861). The PD map exhibited good performance in differentiating epidermal growth factor receptor (EGFR) expression levels (AUC: 0.706~0.732) and histological type (AUC: 0.650~0.660). T2_minimum was highest correlated with Epstein-Barr virus (EBV) DNA levels (r =  - 0.419), and PD_75th percentile exhibited the highest performance in distinguishing positive and negative EBV DNA groups (AUC: 0.721). T1_minimum was statistically correlated with EA-IgA expression (r =  - 0.313). Additionally, several histogram parameters were negatively correlated with tumor stage (T stage: r =  - 0.259 ~ - 0.301; N stage: r =  - 0.348 ~  - 0.456; clinical stage: r =  - 0.419).

CONCLUSIONS

Histogram parameters of SyMRI could reflect tissue intrinsic characteristics and showed potential value in assessing the Ki-67 and EGFR expression levels, histological type, EBV DNA level, EA-IgA, and tumor stage.

KEY POINTS

• SyMRI combined with histogram analysis may help clinicians to assess different prognostic factor statuses in nasopharyngeal carcinoma. • The PD map exhibited good discriminating performance in the Ki-67 and EGFR expression levels. • Histogram parameters of SyMRI were negatively correlated with EBV-related blood biomarkers and TNM stage.

Non-Invasive Monitoring of Increased Fibrotic Tissue and Hyaluronan Deposition in the Tumor Microenvironment in the Advanced Stages of Pancreatic Ductal Adenocarcinoma

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease with a poor prognosis. A better understanding of the tumor microenvironment may help better treat the disease. Magnetic resonance imaging may be a great tool for monitoring the tumor microenvironment at different stages of tumor evolution. Here, we used multi-parametric magnetic resonance imaging techniques to monitor underlying pathophysiologic processes during the advanced stages of tumor development and correlated with histologic measurements.

Abstract

Pancreatic ductal adenocarcinomas are characterized by a complex and robust tumor microenvironment (TME) consisting of fibrotic tissue, excessive levels of hyaluronan (HA), and immune cells. We utilized quantitative multi-parametric magnetic resonance imaging (mp-MRI) methods at 14 Tesla in a genetically engineered KPC (Kras^LSL-G12D/+, Trp53^LSL-R172H/+, Cre) mouse model to assess the complex TME in advanced stages of tumor development. The whole tumor, excluding cystic areas, was selected as the region of interest for data analysis and subsequent statistical analysis. Pearson correlation was used for statistical inference. There was a significant correlation between tumor volume and T2 (r = −0.66), magnetization transfer ratio (MTR) (r = 0.60), apparent diffusion coefficient (ADC) (r = 0.48), and Glycosaminoglycan-chemical exchange saturation transfer (GagCEST) (r = 0.51). A subset of mice was randomly selected for histological analysis. There were positive correlations between tumor volume and fibrosis (0.92), and HA (r = 0.76); GagCEST and HA (r = 0.81); and MTR and CD31 (r = 0.48). We found a negative correlation between ADC low-b (perfusion) and Ki67 (r = −0.82). Strong correlations between mp-MRI and histology results suggest that mp-MRI can be used as a non-invasive tool to monitor the tumor microenvironment.

Intravital microscopy of tumor vessel morphology and function using a standard fluorescence microscope

Purpose

The purpose of the study was to demonstrate the performance and possible applications of an intravital microscopy assay using a standard fluorescence microscope.

Methods

Melanoma and pancreatic ductal adenocarcinoma xenografts were initiated in dorsal window chambers and subjected to repeated intravital microscopy. The entire tumor vasculature as well as the normal tissue surrounding the tumor was imaged simultaneously with high spatial and temporal resolution. Vascular morphology images were recorded by using transillumination, and vascular masks were produced to quantify vessel density, vessel diameter, vessel segment length, and vessel tortuosity. First-pass imaging movies were recorded after an intervenous injection of a fluorescent marker and were used to investigate vascular function. Lymphatics were visualized by intradermal injections of a fluorescent marker.

Results

The intravital microscopy assay was used to study tumor growth and vascularization, tumor vessel morphology and function, tumor-associated lymphatics, and vascular effects of acute cyclic hypoxia and antiangiogenic treatment. The assay was sensitive to tumor-line differences in vascular morphology and function and detected tumor-induced lymphatic dilation. Acute cyclic hypoxia induced angiogenesis and increased the density of small diameter vessels and blood supply times, whereas antiangiogenic treatment selectively removed small-diameter vessels, reduced blood supply times, and induced hypoxia. Moreover, the window chamber was compatible with magnetic resonance imaging (MRI), and parametric images derived by dynamic contrast-enhanced MRI were shown to reflect vascular morphology and function.

Conclusions

The presented assay represents a useful and affordable alternative to intravital microscopy assays using confocal and multi-photon microscopes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05243-0.

Characterisation of Biological Materials at THz Frequencies by Attenuated Total Reflection: Lard

The penetration depth of an evanescent wave in Attenuated Total Reflection (ATR) is dependent on the wavelength of the radiation utilised. At THz frequencies, the penetration depth into biological tissues is in the order of 0.1 to 0.5 mm; rendered pig lard was used as a model sample in this study. A method for the direct measurement of the evanescent wave penetration depth is presented which allows for the estimation of the dispersion of the complex refractive index by using the reflection of the evanescent wave from varying sample depths. The method employs frustrated total internal reflection, and has been demonstrated by using the THz/Far-IR beamline at the Australian synchrotron, and modelled using finite difference time domain (FDTD) simulations.

Renal carcinoma CD105-/CD44- cells display stem-like properties in vitro and form aggressive tumors in vivo

Clear cell renal cell carcinoma (ccRCC) is the most common kidney cancer. Prognosis for ccRCC is generally poor since it is largely resistant to chemo- and radiotherapy. Many studies suggested that cancer stem cells/tumor initiating cells (CSCs/TICs) are responsible for development of tumor, disease progression, aggressiveness, metastasis and drug resistance. However, tumorigenic potential of CSCs/TICs isolated from established RCC cell lines – basic ccRCC research model – has never been investigated in vivo. CD105+, CD105−, CD44+ and CD44− as well as CD44−/CD105− CD44+/CD105+ and CD44−/CD105+ cells were isolated from Caki-1 RCC cell line, confirming coexistence of multiple subpopulations of stem-related phenotype in stable cell line. Sorted cells were injected subcutaneously into NOD SCID mice and tumor growth was monitored with MRI and PET/CT. Tumor growth was observed after implantation of CD105+, CD44+, CD44−, CD44−/CD105+ and CD44−/CD105− but not CD105− or CD44+/CD105+. Implantation of CD44−/CD105− cells induced tumors that were characterized by longer T1 and distinct metabolic pattern than other tumors. All the tumors were characterized by low uptake of [18F]FDG. CD105+ and CD44− tumors expresses Nanog and Oct-4, while CD44− tumors additionally expressed endothelial cell marker - CD31.

Choosing The Right Animal Model for Renal Cancer Research

The increase in the life expectancy of patients with renal cell carcinoma (RCC) in the last decade is due to changes that have occurred in the area of preclinical studies. Understanding cancer pathophysiology and the emergence of new therapeutic options, including immunotherapy, would not be possible without proper research. Before new approaches to disease treatment are developed and introduced into clinical practice they must be preceded by preclinical tests, in which animal studies play a significant role. This review describes the progress in animal model development in kidney cancer research starting from the oldest syngeneic or chemically-induced models, through genetically modified mice, finally to xenograft, especially patient-derived, avatar and humanized mouse models. As there are a number of subtypes of RCC, our aim is to help to choose the right animal model for a particular kidney cancer subtype. The data on genetic backgrounds, biochemical parameters, histology, different stages of carcinogenesis and metastasis in various animal models of RCC as well as their translational relevance are summarized. Moreover, we shed some light on imaging methods, which can help define tumor microstructure, assist in the analysis of its metabolic changes and track metastasis development.

Computational phantom study of frozen melanoma imaging at 0.45 terahertz

Terahertz radiation (THz) is highly absorbed by liquid water. This creates the possibility of medical imaging on the basis of the water content difference between normal and diseased tissue. The effective penetration of THz is limited, however, to a tissue depth of 0.2-0.3 mm at body temperature. A unique feature of the 0.1-2.0 THz frequency is that there is a high disparity between liquid water absorption and ice absorption, with ice being 100 times more permeable to the radiation than liquid water. This results in 90% of the radiation surviving to 1.0 mm in ice, permitting the imaging of frozen tissues to a depth of 5.0 mm. This method is practical as an in vivo procedure before or during surgical excision. Finite difference time domain (FDTD) computational modeling of frozen normal skin and frozen melanoma was undertaken using tissue phantoms. The study suggests that sufficient contrast exists to differentiate normal frozen skin and melanoma on the basis of the difference of water content alone. When the melanin pigment in melanomas is modeled as a significant absorber of THz, the contrast changes. Based on the modeling, further exploration of the "THz-skin freeze" imaging technique is justified. In the modeling, the boundary between the frozen tissue and non-frozen tissue is shown to be strongly reflective. If the reflective properties of the boundary are substantiated, the "THz-skin freeze" technique will have applications in other areas of skin diagnostics and therapeutics. Bioelectromagnetics. 40:118-127, 2019. © 2019 Bioelectromagnetics Society.

Evaluation of pancreatic tumor development in KPC mice using multi-parametric MRI

Background

Pancreatic ductal adenocarcinoma (PDA) is a fatal disease with very poor prognosis. Development of sensitive and noninvasive methods to monitor tumor progression in PDA is a critical and unmet need. Magnetic resonance imaging (MRI) can noninvasively provide information regarding underlying pathophysiological processes such as necrosis, inflammatory changes and fibrotic tissue deposition.

Methods

A genetically engineered KPC mouse model that recapitulates human PDA was used to characterize disease progression. MR measures of T₁ and T₂ relaxation times, magnetization transfer ratio (MTR), diffusion and chemical exchange saturation transfer were compared in two separate phases i.e. slow and rapid growth phase of tumor. Fibrotic tissue accumulation was assessed histologically using Masson’s trichrome staining. Pearson correlation coefficient (r) was computed to assess the relationship between the fibrotic tissue accumulation and different MR parameters.

Results

There was a negative correlation between amide proton transfer signal intensity and tumor volume (r = − 0.63, p = 0.003) in the slow growth phase of the tumor development. In the terminal stage of rapid growth phase of the tumor development MTR was strongly correlated with tumor volume (r = 0.62, p = 0.008). Finally, MTR was significantly correlated with % fibrosis (r = 0.87; p < 0.01), followed by moderate correlation between tumor volume (r = 0.42); T₁ (r = − 0.61), T₂ (r = − 0.61) and accumulation of fibrotic tissue.

Conclusions

Here we demonstrated, using multi-parametric MRI (mp-MRI), that MRI parameters changed with tumor progression in a mouse model of PDA. Use of mp-MRI may have the potential to monitor the dynamic changes of tumor microenvironment with increase in tumor size in the transgenic KPC mouse model of pancreatic tumor.

Electronic supplementary material

The online version of this article (10.1186/s40644-018-0172-6) contains supplementary material, which is available to authorized users.

Tumor T1 Relaxation Time for Assessing Response to Bevacizumab Anti-Angiogenic Therapy in a Mouse Ovarian Cancer Model

Purpose

To assess whether T₁ relaxation time of tumors may be used to assess response to bevacizumab anti-angiogenic therapy. Procedures: 12 female nude mice bearing subcutaneous SKOV3ip1-LC ovarian tumors were administered bevacizumab (6.25ug/g, n=6) or PBS (control, n=6) therapy twice a week for two weeks. T₁ maps of tumors were generated before, two days, and 2 weeks after initiating therapy. Tumor weight was assessed by MR and at necropsy. Histology for microvessel density, proliferation, and apoptosis was performed.

Results

Bevacizumab treatment resulted in tumor growth inhibition (p<0.04, n=6), confirming therapeutic efficacy. Tumor T₁ relaxation times increased in bevacizumab treated mice 2 days and 2 weeks after initiating therapy (p<.05, n=6). Microvessel density decreased 59% and cell proliferation (Ki67+) decreased 50% in the bevacizumab treatment group (p<.001, n=6), but not apoptosis.

Conclusions

Findings suggest that increased tumor T₁ relaxation time is associated with response to bevacizumab therapy in ovarian cancer model and might serve as an early indicator of response.

Assessment of tumor necrotic fraction by dynamic contrast-enhanced MRI: a preclinical study of human tumor xenografts with histopathologic correlation

Contrary to the common notion that tumor necrotic regions are non-enhancing after contrast administration, recent evidence has shown that necrotic regions exhibit delayed and slow uptake of gadolinium tracer on dynamic contrast-enhanced MRI (DCE MRI). The purpose of this study is to explore whether the mapping of tumor voxels with delayed and slow enhancement on DCE MRI can be used to derive estimates of tumor necrotic fraction. Patient-derived tumor xenograft lines of seven human cancers were implanted in 26 mice which were subjected to DCE MRI performed using a spoiled gradient recalled sequence. Gadolinium tracer concentration was estimated using the variable flip angle technique. To identify tumor voxels exhibiting delayed and slow uptake of contrast medium, clustering analysis was performed using a k-means clustering algorithm that classified tumor voxels according to their contrast enhancement patterns. Comparison of the percentage of tumor voxels exhibiting delayed and slow enhancement with the tumor necrotic fraction estimated on histology showed a strong correlation (r = 0.962, p < 0.001). The mapping of tumor regions with delayed and slow contrast uptake on DCE MRI correlated strongly with tumor necrotic fraction, and can potentially serve as a non-invasive imaging surrogate for the in vivo assessment of necrotic fraction.

Tumour T1 changes in vivo are highly predictive of response to chemotherapy and reflect the number of viable tumour cells--a preclinical MR study in mice

Background

Effective chemotherapy rapidly reduces the spin–lattice relaxation of water protons (T₁) in solid tumours and this change (ΔT₁) often precedes and strongly correlates with the eventual change in tumour volume (TVol). To understand the biological nature of ΔT₁, we have performed studies in vivo and ex vivo with the allosteric mTOR inhibitor, everolimus.

Methods

Mice bearing RIF-1 tumours were studied by magnetic resonance imaging (MRI) to determine TVol and T₁, and MR spectroscopy (MRS) to determine levels of the proliferation marker choline and levels of lipid apoptosis markers, prior to and 5 days (endpoint) after daily treatment with vehicle or everolimus (10 mg/kg). At the endpoint, tumours were ablated and an entire section analysed for cellular and necrotic quantification and staining for the proliferation antigen Ki67 and cleaved-caspase-3 as a measure of apoptosis. The number of blood-vessels (BV) was evaluated by CD31 staining. Mice bearing B16/BL6 melanoma tumours were studied by MRI to determine T₁ under similar everolimus treatment. At the endpoint, cell bioluminescence of the tumours was measured ex vivo.

Results

Everolimus blocked RIF-1 tumour growth and significantly reduced tumour T₁ and total choline (Cho) levels, and increased polyunsaturated fatty-acids which are markers of apoptosis. Immunohistochemistry showed that everolimus reduced the %Ki67⁺ cells but did not affect caspase-3 apoptosis, necrosis, BV-number or cell density. The change in T₁ (ΔT₁) correlated strongly with the changes in TVol and Cho and %Ki67⁺. In B16/BL6 tumours, everolimus also decreased T₁ and this correlated with cell bioluminescence; another marker of cell viability. Receiver-operating-characteristic curves (ROC) for everolimus on RIF-1 tumours showed that ΔT₁ had very high levels of sensitivity and specificity (ROC_AUC = 0.84) and this was confirmed for the cytotoxic patupilone in the same tumour model (ROC_AUC = 0.97).

Conclusion

These studies suggest that ΔT₁ is not a measure of cell density but reflects the decreased number of remaining viable and proliferating tumour cells due to perhaps cell and tissue destruction releasing proteins and/or metals that cause T₁ relaxation. ΔT₁ is a highly sensitive and specific predictor of response. This MRI method provides the opportunity to stratify a patient population during tumour therapy in the clinic.

Assessment of colorectal hepatic metastases by quantitative T2 relaxation time

AIM

To determine the T(2) relaxation time of colorectal hepatic metastases and changes in T(2) relaxation times following chemotherapy.

MATERIALS AND METHODS

42 patients with 96 hepatic colorectal metastases underwent baseline MRI. Axial T(1), T(2) and multi-echo GRASE sequences were acquired. ROIs were drawn on T(2) relaxation maps, obtained from GRASE images, encompassing metastasis and normal liver to record T(2) relaxation time values. In 11 patients with 28 metastases, MRI was repeated using same protocol at 6 weeks following chemotherapy. The median pre-treatment T(2) values of metastases and normal liver were compared using the Mann-Whitney test. The pre- and post-treatment median T(2) values of metastases were compared using the Wilcoxon-Rank test for responding (n=16) and non-responding (n=12) lesions defined by RECIST criteria. The change in T(2) values (ΔT(2)) were compared and correlated with percentage change in lesion size.

RESULTS

There was no difference in the pre-treatment median T(2) of metastases between responding (67.3±8.6) and non-responding metastases (71.4±16.5). At the end of chemotherapy, there was a decrease in the median T(2) of responding lesions (61.6±12.6) p=0.83, and increase in non-responding lesions (76.2±18.4) p=0.03, but these were not significantly different from the pre-treatment values. There was no significant difference in ΔT(2) of responding and non-responding lesions (p=0.18) and no correlation was seen between size change and ΔT(2) (coefficient=0.3).

CONCLUSION

T(2) relaxation time does not appear to predict response of colorectal liver metastasis to chemotherapy.

Terahertz pulsed imaging of freshly excised human colonic tissues

We present the results from a feasibility study which measures properties in the terahertz frequency range of excised cancerous, dysplastic and healthy colonic tissues from 30 patients. We compare their absorption and refractive index spectra to identify trends which may enable different tissue types to be distinguished. In addition, we present statistical models based on variations between up to 17 parameters calculated from the reflected time and frequency domain signals of all the measured tissues. These models produce a sensitivity of 82% and a specificity of 77% in distinguishing between healthy and all diseased tissues and a sensitivity of 89% and a specificity of 71% in distinguishing between dysplastic and healthy tissues. The contrast between the tissue types was supported by histological staining studies which showed an increased vascularity in regions of increased terahertz absorption.

ADC response to radiation therapy correlates with induced changes in radiosensitivity

PURPOSE

Magnetic resonance imaging was used to compare the responses of human glioma tumor xenografts to a single fraction of radiation, where a change in radiosensitivity was induced by use of a suture-based ligature.

METHODS

Ischemia was induced by use of a suture-based ligature. Six mice were treated with 800 cGy of 200 kVp x rays while the ligature was applied. An additional six mice had the ligature applied for the same length of time but were not irradiated. Quantitative maps of each tumor were produced of water apparent diffusion coefficient (ADC) and transverse relaxation time (T2). Mice were imaged before and at multiple points after treatment. Volumetric, ADC, and T2 responses of the ligated groups were compared to previously measured responses of the same tumor model to the same radiation treatment, as well as those from an untreated control group.

RESULTS

Application of the ligature without irradiation did not affect tumor ADC values, but did produce a temporary decrease in tumor T2 values. Average tumor T2 was reduced by 6.2% 24 h after the ligature was applied. Average tumor ADC increased by 9.6% 7 days after irradiation with a ligature applied. This response was significantly less than that observed in the same tumor model when no ligature is present (21.8% at 7 days after irradiation).

CONCLUSIONS

These observations indicate that the response of ADC to radiation therapy is not determined entirely by physical dose deposition, but at least in part by radiosensitivity and resultant biological response.

Study of water concentration measurement in thin tissues with terahertz-wave parametric source

Water concentration and distribution in biotissues are important factors in many applications. THz-wave is a viable tool for water content measurement due to its highly sensitivity to water. In this study, the measuring errors of water concentration using THz-wave induced by transmittance and sample thickness were analyzed theoretically. The chosen basis for sample thickness and measuring THz frequency were presented theoretically. Measurements of the water two-dimensional mapping in different animal tissue samples were demonstrated experimentally, which clearly shows the spatial distribution of the tissues.

Quantified tumor t1 is a generic early-response imaging biomarker for chemotherapy reflecting cell viability

PURPOSE

Identification of a generic response biomarker by comparison of chemotherapeutics with different action mechanisms on several noninvasive biomarkers in experimental tumor models.

EXPERIMENTAL DESIGN

The spin-lattice relaxation time of water protons (T(1)) was quantified using an inversion recovery-TrueFISP magnetic resonance imaging method in eight different experimental tumor models before and after treatment at several different time points with five different chemotherapeutics. Effects on T(1) were compared with other minimally invasive biomarkers including vascular parameters, apparent diffusion coefficient, and interstitial fluid pressure, and were correlated with efficacy at the endpoint and histologic parameters.

RESULTS

In all cases, successful chemotherapy significantly lowered tumor T(1) compared with vehicle and the fractional change in T(1) (DeltaT(1)) correlated with the eventual change in tumor size (range: r(2) = 0.21, P < 0.05 to r(2) = 0.73, P < 0.0001), except for models specifically resistant to that drug. In RIF-1 tumors, interstitial fluid pressure was decreased, but apparent diffusion coefficient and permeability increased in response to the microtubule stabilizer patupilone and 5-fluorouracil. Although DeltaT(1) was small (maximum of -20%), the variability was very low (5%) compared with other magnetic resonance imaging methods (24-48%). Analyses ex vivo showed unchanged necrosis, increased apoptosis, and decreased %Ki67 and total choline, but only Ki67 and choline correlated with DeltaT(1). Correlation of Ki67 and DeltaT(1) were observed in other models using patupilone, paclitaxel, a VEGF-R inhibitor, and the mammalian target of rapamycin inhibitor everolimus.

CONCLUSIONS

These results suggest that a decrease in tumor T(1) reflects hypocellularity and is a generic marker of response. The speed and robustness of the method should facilitate its use in clinical trials.

Tumor vascularity assessed by magnetic resonance imaging and intravital microscopy imaging

Gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is considered to be a useful method for characterizing the vascularity of tumors. However, detailed studies of experimental tumors comparing DCE-MRI-derived parametric images with images of the morphology and function of the microvascular network have not been reported. In this communication, we describe a novel MR-compatible mouse dorsal window chamber and report comparative DCE-MRI and intravital microscopy studies of A-07-GFP tumors xenografted to BALB/c nu/nu mice. Blood supply time (BST) images (i.e., images of the time from when arterial blood enters a tumor through the supplying artery until it reaches a vessel segment within the tumor) and morphologic images of the microvascular network were produced by intravital microscopy. Images of E.F (E is the initial extraction fraction of Gd-DTPA and F is perfusion) were produced by subjecting DCE-MRI series to Kety analysis. The E.F images mirrored the morphology (microvascular density) and the function (BST) of the microvascular networks well. Tumor regions showing high E.F values colocalized with tumor regions showing high microvascular density and low BST values. Significant correlations were found between E.F and microvascular density and between E.F and BST, both within and among tumors.

Cranial MRI of small rodents using a clinical MR scanner

Increasing numbers of small animal models are in use in the field of neuroscience research. Magnetic resonance imaging (MRI) provides an excellent method for non-invasive imaging of the brain. Using three-dimensional (3D) MR sequences allows lesion volumetry, e.g. for the quantification of tumor size. Specialized small-bore animal MRI scanners are available for high-resolution MRI of small rodents' brain, but major drawbacks of this dedicated equipment are its high costs and thus its limited availability. Therefore, more and more research groups use clinical MR scanners for imaging small animal models. But to achieve a reasonable spatial resolution at an acceptable signal-to-noise ratio with these scanners, some requirements concerning sequence parameters have to be matched. Thus, the aim of this paper was to present in detail a method how to perform MRI of small rodents brain using a standard clinical 1.5 T scanner and clinically available radio frequency coils to keep material costs low and to circumvent the development of custom-made coils.

Dynamic contrast-enhanced magnetic resonance imaging of human melanoma xenografts with necrotic regions

PURPOSE

To investigate whether high-resolution images of necrotic regions in tumors can be derived from gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) series.

MATERIALS AND METHODS

E-13 human melanoma xenografts were used as preclinical models of human cancer. DCE-MRI was performed at a voxel size of 0.23 x 0.47 x 2.0 mm3 with the use of spoiled gradient recalled sequences. Tumor images of E . F (E is the initial extraction fraction of Gd-DTPA and F is blood perfusion) and lambda (the partition coefficient of Gd-DTPA, which is proportional to extracellular volume fraction) were produced by subjecting DCE-MRI series to Kety analysis, and these images were compared with histological preparations from the imaged slices.

RESULTS

Strong correlations were found between fraction of necrotic tissue and fraction of voxels with lambda > lambdaL for lambdaL values of 0.4 to 0.6. Binary lambda images differentiating between lambda values > lambdaL and lambda values < lambdaL were found to mirror necrotic regions well in tumors with large necroses. However, necrotic foci that were small compared with the voxel size were not detectable.

CONCLUSION

Clinically relevant images of necrotic tumor regions can be obtained for E-13 melanomas by subjecting Gd-DTPA-based DCE-MRI series to Kety analysis.

Assessment of microvascular density, extracellular volume fraction, and radiobiological hypoxia in human melanoma xenografts by dynamic contrast-enhanced MRI

PURPOSE

To investigate whether gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may be a useful method for assessing fraction of radiobiologically hypoxic cells in tumors.

MATERIALS AND METHODS

A-07 and R-18 human melanoma xenografts were used as preclinical tumor models. DCE-MRI was performed at a voxel size of 0.23 x 0.47 x 2.0 mm(3). Tumor images of E . F (E is the initial extraction fraction of Gd-DTPA and F is blood perfusion) and lambda (the partition coefficient of Gd-DTPA) were produced by subjecting DCE-MRI series to Kety analysis. Microvascular density and extracellular volume fraction (ECVF) were determined by analysis of histological preparations. The fraction of radiobiologically hypoxic cells was measured by the paired survival curve method.

RESULTS

E . F correlated with microvascular density, and lambda correlated with ECVF. The fraction of hypoxic cells was approximately 6.5-fold higher in R-18 tumors than in A-07 tumors, consistent with the observation that A-07 tumors showed higher values for E . F and microvascular density and lower cell density (i.e., higher values for lambda and ECVF) than R-18 tumors.

CONCLUSION

E . F and lambda images obtained by Kety analysis of DCE-MRI series contain information that may be utilized to estimate the extent of radiobiological hypoxia in tumors.

Magnetic resonance imaging measurements of vascular permeability and extracellular volume fraction of breast tumors by dynamic Gd-DTPA-enhanced relaxometry

Vascular permeability (k(ep), min(-1)) and extracellular volume fraction (v(e)) are tissue parameters of great interest to characterize malignant tumor lesions. Indeed, it is well known that tumors with high blood supply better respond to therapy than poorly vascularized tumors, and tumors with large extracellular volume tend to be more malignant than tumors showing lower extracellular volume. Furthermore, the transport of therapeutic agents depends on both extracellular volume fraction and vessel permeability. Thus, before treatment, these tissue parameters may prove useful to evaluate tumor aggressiveness and to predict responsiveness to therapy and variations during cytotoxic therapies could allow to assess treatment efficacy and early modified therapy schedules in case of poor responsiveness. As a consequence, there is a need to develop methods that could be routinely used to determine these tissue parameters. In this work, blood-tissue permeability and extracellular volume fraction information were derived from magnetic resonance imaging dynamic longitudinal relaxation rate (R(1)) mapping obtained after an intravenous bolus injection of Gd-DTPA in a group of 92 female patients with breast lesions, 68 of these being histologically proven to be with carcinoma. For the sake of comparison, 24 benign lesions were studied. The measurement protocol based on two-dimensional gradient echo sequences and a monoexponential plasma kinetic model was that validated in the occasion of previous animal experiments. As a consequence of neoangiogenesis, results showed a higher permeability in malignant than in benign lesions, whereas the extracellular volume fraction value did not allow any discrimination between benign and malignant lesions. The method, which can be easily implemented whatever the imaging system used, could advantageously be used to quantify lesion parameters (k(ep) and v(e)) in routine clinical imaging. Because of its large reproducibility, the method could be useful for intersite comparisons and follow-up studies.

Terahertz pulsed spectroscopy of human Basal cell carcinoma

Good contrast is seen between normal tissue and regions of tumor in terahertz pulsed imaging of basal cell carcinoma (BCC). To date, the source of contrast at terahertz frequencies is not well understood. In this paper we present results of a spectroscopy study comparing the terahertz properties (absorption coefficient and refractive index) of excised normal human skin and BCC. Both the absorption coefficient and refractive index were higher for skin that contained BCC. The difference was statistically significant over the range 0.2 to 2.0 THz (6.6 cm(-1) to 66.6 cm(-1)) for absorption coefficient and 0.25 to 0.90 THz (8.3 cm(-1) to 30 cm(-1)) for refractive index. The maximum difference for absorption was at 0.5 THz(16.7 cm(-1)). These changes are consistent with higher water content. These results account for the contrast seen in terahertz images of BCC and explain why parameters relating to the reflected terahertz pulse provide information about the lateral spread of the tumor. Knowing the properties of the tissue over the terahertz frequency range will enable the use of mathematical models to improve understanding of the terahertz response of normal and diseased tissue.

Terahertz pulsed imaging of human breast tumors

The feasibility of using terahertz pulsed imaging to map margins of exposed breast tumors was investigated by imaging 22 excised human breast tissue specimens with carcinoma excised from 22 women (mean age, 59 years; range, 39-80 years). The study was approved by the local ethics research committee, and informed consent was obtained from all patients. The size and shape of tumor regions on terahertz images were compared with those identified at histopathologic examination of the imaged section. Two image parameters were investigated: the minimum of the terahertz impulse function and the ratio of the minimum to the maximum of the terahertz impulse function. The correlation coefficient for the tumor area on images compared with that on a photomicrograph of all 22 samples was greater than 0.82 for both parameters. The shape of the tumor regions on terahertz images also correlated well with that on a photomicrograph (median Spearman rank correlation coefficient, 0.69). Findings of this study demonstrate the potential of terahertz pulsed imaging to depict both invasive breast carcinoma and ductal carcinoma in situ under controlled conditions and encourage further studies to determine the sensitivity and specificity of the technique.

Fluctuations in pO2 in irradiated human melanoma xenografts

Several studies have demonstrated that untreated tumors may show significant fluctuations in tissue oxygen tension (pO(2)). Radiation treatment may induce changes in the tumor microenvironment that alter the pO(2) fluctuation pattern. The purpose of the present study was to investigate whether pO(2) fluctuations may also occur in irradiated tumors. A-07 human melanoma xenografts were irradiated with single doses of 0, 5 or 10 Gy. Fluctuations in pO(2) were recorded with OxyLite probes prior to irradiation and 24 and 72 h after the radiation exposure. Radiation-induced changes in the tumor microenvironment (i.e. blood perfusion and extracellular volume fraction) were assessed by dynamic contrast-enhanced magnetic resonance imaging. Seventy-two hours after 10 Gy, tumor blood perfusion had decreased to approximately 40% of that prior to irradiation, whereas the extracellular volume fraction had increased by approximately 25%. Fluctuations in pO(2) were seen in most tumors, irrespective of radiation dose and time after irradiation. The mean pO(2), the number of fluctuations around the mean pO(2), the number of fluctuations around threshold pO(2) values of 1, 2, 3, 5, 7 and 10 mmHg, and the amplitude of the fluctuations were determined for each pO(2) trace. No significant differences were detected between irradiated and unirradiated tumors. The results showed that pO(2) fluctuations may occur in irradiated tumors and that the pO(2) fluctuation pattern in A-07 tumors exposed to 5 or 10 Gy is similar to that in untreated tumors. Consequently, these doses did not induce changes in the tumor microenvironment that were sufficient to cause detectable alterations in the pO(2) fluctuation pattern.

(1)H relaxation times of metabolites in biological samples obtained with nondestructive ex-vivo slow-MAS NMR

Methods suitable for measuring (1)H relaxation times such as T(1), T(2) and T(1rho) of metabolites in small, intact biological objects including live cells, excised organs and tissues, oil seeds etc. are developed in this work. This was achieved by combining inversion-recovery, spin-echo, or a spin-lock segment with the phase-adjusted spinning sideband (PASS) technique, which was applied at low sample-spinning rates. Here, PASS was used to produce high-resolution (1)H spectra in a nondestructive way so that the relaxation parameters of individual metabolite could be determined. The methodologies were demonstrated by measuring (1)H T(1), T(2), and T(1rho) of metabolites in excised rat liver at a spinning rate of 40 Hz.

Analysis of mouse brain using a clinical 1.5 T scanner and a standard small loop surface coil

With increasing numbers of in vivo experiments in the field of neuroscience, the interest in methods for in vivo imaging of animal brains as small as those of mice has increased. Because highly specialized small bore scanners with high field strengths are not commonly available, clinical magnetic resonance imaging (cMRI) scanners have been used in the past to image rat and more recently also mouse brains in combination with specifically developed RF coils. These studies have demonstrated that imaging of small animal brains is feasible, and that tumor volumes measured by cMRI correlate well with histological tumor volume analysis. This protocol describes the cMRI settings at 1.5 T for imaging of mouse brain with resolutions up to 120 x 120 microm using an inexpensive, commercially available small loop surface coil. This allows easy establishment of a small animal MRI facility without the need for cost intensive dedicated small animal scanners or special custom made coils. In this study, we demonstrate high-resolution imaging of intracranial xenografts in a mouse glioma model and monitor the treatment effect of external field irradiation by cMRI.

Assessment of fraction of radiobiologically hypoxic cells in human melanoma xenografts by dynamic contrast-enhanced MRI

A noninvasive method for assessment of the extent of hypoxia in experimental and human tumors is highly needed. In this study, the potential usefulness of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was investigated, using gadopentetate dimeglumine (Gd-DTPA) as contrast agent and A-07 human melanoma xenografts as tumor model. DCE-MRI was performed at a voxel size of 0.3 x 0.6 x 2.0 mm3 with spoiled gradient-recalled sequences. Images of E . F (E is the initial extraction fraction of Gd-DTPA and F is perfusion) and lambda (the partition coefficient of Gd-DTPA, which is proportional to extracellular volume fraction) were obtained by Kety analysis of DCE-MRI data. The study was based on the hypothesis that hypoxic tissue would have low E . F (i.e., poor oxygen supply) and/or low lambda (i.e., high cell density and, hence, high oxygen consumption rate). Twenty-two tumors were first subjected to DCE-MRI and then to measurement of fraction of hypoxic cells, using a radiobiological assay. E . F was found to be strongly correlated to fraction of hypoxic cells (P < 0.000001), whereas significant correlation between lambda and fraction of hypoxic cells could not be detected. It is thus possible that E . F may be a useful parameter for the extent of hypoxia in experimental and human tumors with physiologic properties similar to those of A-07 tumors. This possibility warrants further studies involving experimental tumors of several lines, as well as human tumors.

Changes in intratumor heterogeneity in blood perfusion in intradermal human melanoma xenografts during tumor growth assessed by DCE-MRI

The purpose of this study was to use dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to search for systematic intratumor heterogeneity in blood perfusion in human melanoma xenografts growing intradermally in BALB/c-nu/nu mice. Six xenografted tumors of an amelanotic human melanoma line (A-07) were included in the study. DCE-MRI was performed daily for 5 days by using spoiled-gradient recalled sequences. Tumor images of E.F (E is initial extraction fraction and F is perfusion) were produced by subjecting DCE-MRI data to Kety analysis. E.F was used as a measure of tumor blood perfusion, since comparative studies have shown that E.F is closely related to blood perfusion in A-07 tumors. The E.F images indicated that the intratumor heterogeneity in blood perfusion was similar in all investigated tumors. The blood perfusion was low in the center of the tumors and increased toward the tumor periphery in the dorsal and ventral direction by a factor of 3-4, but not in the lateral and medial direction. The magnitude of the heterogeneity increased by a factor of approximately 2 during tumor growth. In conclusion, intradermal human melanoma xenografts show significant systematic intratumor heterogeneity in blood perfusion.

Intratumor heterogeneity in blood perfusion in orthotopic human melanoma xenografts assessed by dynamic contrast-enhanced magnetic resonance imaging

PURPOSE

To determine the intratumor heterogeneity in blood perfusion of orthotopic human melanoma xenografts by use of gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

MATERIALS AND METHODS

Orthotopic xenografts of an amelanotic human melanoma cell line (A-07) were scanned sagittally, coronally, and axially in three subsequent DCE-MRI sessions, using spoiled gradient recalled sequences, a voxel size of 0.31x0.62x2.0 mm3, and an interleaving acquisition method to avoid slice gaps. Tumor images of E . F (E is initial extraction fraction and F is perfusion) were produced by subjecting the DCE-MRI data to Kety analysis. E . F was used as a parameter for tumor blood perfusion, since E for Gd-DTPA is close to unity in A-07 tumors.

RESULTS

All A-07 tumors subjected to investigation showed anisotropic radial heterogeneity in blood perfusion. The blood perfusion was low in the center of the tumors and increased toward the tumor periphery in the cranial, dorsal, caudal, and ventral directions, but not in the lateral and medial directions. In addition, 9 of 10 tumors showed blood perfusion hot spots in central or nonperipheral regions. The hot spots differed significantly between tumors in size, shape, location, and intensity, and appeared to be governed by stochastic processes. This heterogeneity superimposed the radial heterogeneity, but did not overshadow it in any tumor.

CONCLUSION

Orthotopic human melanoma xenografts show significant intratumor heterogeneity in blood perfusion. This heterogeneity is made up of two distinctly different components, one stochastic and one nonstochastic radial component. The radial component is anisotropic and dominant and is superimposed by the stochastic component.

Comparison of tumor blood perfusion assessed by dynamic contrast-enhanced MRI with tumor blood supply assessed by invasive imaging

PURPOSE

To evaluate the potential of Gd-DTPA-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) for providing high-resolution tumor blood perfusion images.

MATERIALS AND METHODS

Xenografted tumors from two amelanotic human melanoma lines (A-07 and R-18) were used as preclinical models of human cancer. DCE-MRI was performed at a voxel size of 0.5 x 0.2 x 2.0 mm(3) with the use of spoiled gradient recalled sequences. We produced tumor images of E . F (where E is the initial extraction fraction, and F is perfusion) by subjecting the DCE-MRI data to Kety analysis, and then compared those images with images of tumor blood supply. We obtained high-resolution tumor blood supply images using the Bioscope silicon strip detector system to measure the uptake of Na(99m)TcO(4) in histological preparations. We assessed the global blood supply by measuring the tumor uptake of three freely diffusible blood flow tracers: (86)RbCl, [(14)C]IAP, and Na(99m)TcO(4).

RESULTS

E . F was found to mirror the blood supply well in A-07 and R-18 tumors. The mean E . F differed between the A-07 and R-18 tumors by a factor of approximately 1.6, and this difference was similar to the difference in the global blood supply. The intratumor heterogeneity in E . F was significant for tumors of both lines, and this heterogeneity was similar to the intratumor heterogeneity in the blood supply. The intratumor heterogeneity in the blood supply differed slightly between the A-07 and R-18 tumors, and even this difference was mirrored by the E . F images.

CONCLUSION

E . F images of xenografted tumors reflect blood perfusion. This implies that E . F may be a useful parameter for improving cancer diagnostics and individualizing cancer treatment. This possibility deserves to be investigated thoroughly in clinical studies.

Terahertz pulsed imaging of basal cell carcinoma ex vivo and in vivo

BACKGROUND

Terahertz radiation lies between the infrared and microwave regions of the electromagnetic spectrum and can be used to excite large amplitude vibrational modes of molecules and probe the weak interactions between them. Terahertz pulsed imaging (TPI) is a noninvasive imaging technique that utilises this radiation.

OBJECTIVES

To determine whether TPI could differentiate between basal cell carcinoma (BCC) and normal tissue and to test whether it can help facilitate delineation of tumour margins prior to surgery.

METHODS

A portable TPI system was used in the clinic to image 18 BCCs ex vivo and five in vivo.

RESULTS

The diseased tissue showed a change in terahertz properties compared with normal tissue, manifested through a broadening of the reflected terahertz pulse. Regions of disease identified in the terahertz image correlated well with histology.

CONCLUSIONS

This study has confirmed the potential of TPI to identify the extent of BCC in vivo and to delineate tumour margins. Further clinical study of TPI as a surgical tool is now required.

Investigation of microenvironmental factors influencing the longitudinal relaxation times of drugs and other compounds

The aim of this study was to investigate the microenvironmental factors likely to influence the longitudinal relaxation time of MR visible drugs or compounds in vivo at 1.5 T. The relative influence that viscosity, albumin and paramagnetic contrast agent concentrations have on the observed longitudinal relaxation times of three 19F MR detectable drugs and compounds have been investigated. Our data show that for 5-fluorouracil, flucloxacillin and tetrafluorosuccinic acid-containing phantoms, the presence of albumin at normal physiological concentrations will have relaxation effects of the same order of magnitude as that of a commonly clinically administered contrast agent, gadolinium diethylenetriamine pentaacetic acid. The contribution of viscosity is shown, in the examples studied here, to be of minor importance, contributing less than 6.5% to the observed relaxation effects. It is also demonstrated that in the presence of competitive binding of other ligands for common binding sites on albumin, the 19F longitudinal relaxation time of 5-fluorouracil can increase by up to 340% from its value in the absence of the competing ligand. The relevance of the findings to in vivo studies is discussed.

Quantitative assessment of uptake and distribution of iron oxide particles (NC100150) in human melanoma xenografts by contrast-enhanced MRI

The intratumor heterogeneity in uptake of iron oxide particles (NC100150) in human melanoma xenografts was studied by MRI and the uptake was related to the blood volume fraction, BV, and the permeability surface area product, PS, in an attempt to identify transport barriers limiting the delivery of large macromolecular therapeutic agents to tumors. Dynamic MRI was performed by using spoiled gradient recalled sequences and the extravascular uptake of NC100150, BV, and PS were calculated for each tumor voxel by using a two-compartment tissue model. The uptake of NC100150 and BV were low in the tumor center and increased gradually towards the tumor periphery, whereas there was no radial gradient in PS. Significant correlations were found between the voxel values of the parameters. Thus, PS was inversely correlated to BV, and this correlation was stronger in the center than in the periphery of the tumors. The uptake of NC100150 was positively correlated to PS and this correlation was strong in the tumor periphery, where the blood perfusion is high, and weak in the tumor center, where the blood perfusion is low. In contrast, the uptake of NC100150 was not correlated to BV in any tumor region. These observations suggest that the extravascular uptake of NC100150 was limited primarily by the microvascular permeability in the tumor periphery and primarily by the blood perfusion in the tumor center.

In vivostudy of human skin using pulsed terahertz radiation

Studies in terahertz (THz) imaging have revealed a significant difference between skin cancer (basal cell carcinoma) and healthy tissue. Since water has strong absorptions at THz frequencies and tumours tend to have different water content from normal tissue, a likely contrast mechanism is variation in water content. Thus, we have previously devised a finite difference time-domain (FDTD) model which is able to closely simulate the interaction of THz radiation with water. In this work we investigate the interaction of THz radiation with normal human skin on the forearm and palm of the hand in vivo. We conduct the first ever systematic in vivo study of the response of THz radiation to normal skin. We take in vivo reflection measurements of normal skin on the forearm and palm of the hand of 20 volunteers. We compare individual examples of THz responses with the mean response for the areas of skin under investigation. Using the in vivo data, we demonstrate that the FDTD model can be applied to biological tissue. In particular, we successfully simulate the interaction of THz radiation with the volar forearm. Understanding the interaction of THz radiation with normal skin will form a step towards developing improved imaging algorithms for diagnostic detection of skin cancer and other tissue disorders using THz radiation.

Assessment of tumor blood perfusion by high-resolution dynamic contrast-enhanced MRI: A preclinical study of human melanoma xenografts

A noninvasive method to obtain high-resolution images of tumor blood perfusion is needed for individualized cancer treatments. In this study we investigated the potential usefulness of dynamic contrast-enhanced MRI (DCE-MRI), using human melanoma xenografts as models of human cancer. Gadopentetate dimeglumine (Gd-DTPA) was used as the contrast agent, and DCE-MRI was performed at a voxel size of 0.5 x 0.2 x 2.0 mm3 with spoiled gradient-recalled sequences. We obtained images of E. F (where E is the extraction fraction, and F is perfusion) by subjecting DCE-MR images to Kety analysis. We obtained highly reproducible E. F images, which we verified by imaging heterogeneous tumors twice. We hypothesized that the extraction fraction of Gd-DTPA would be high and would not vary significantly in tumor tissue, implying that E. F should be a well-suited parameter for describing tumor blood perfusion. Observations consistent with this hypothesis were made by comparison of E. F-images with immunostained histological preparations from the imaged sections. The E. F images mirrored the histological appearance of the tumor tissue perfectly. Quantitative studies showed that E. F was highest in nonhypoxic tissue with high microvascular density, second highest in nonhypoxic tissue with low microvascular density, third highest in hypoxic tissue, and lowest in necrotic tissue. Moreover, the radial heterogeneity in E. F was almost identical to that in the blood supply, as assessed by the use of Na99mTcO4 as a perfusion tracer. Taken together, our observations show that high-resolution images reflecting tumor blood perfusion can be obtained by DCE-MRI.

Terahertz pulse imaging of ex vivo basal cell carcinoma

Terahertz pulse imaging has been used for the first time to study basal cell carcinoma ex vivo, the most common form of skin cancer. This noninvasive technique uses part of the electromagnetic spectrum in the frequency range 0.1-2.7 THz. A total of 21 samples were imaged; the study was performed blind and results were compared to histology. Each image consisted of possible diseased tissue and normal tissue from the same patient. The diseased tissue showed an increase in absorption compared to normal tissue, which is attributed to either an increase in the interstitial water within the diseased tissue or a change in the vibrational modes of water molecules with other functional groups. Seventeen of the images showed a significant difference between the normal and the diseased tissue. These were confirmed by histology to be basal cell carcinomas. Of the remaining four cases, three showed no contrast and were confirmed as blind controls of normal tissue; the fourth case was a suspected basal cell carcinoma but showed no contrast, and histology showed no tumor. Cross-sections of the terahertz images, showing the terahertz absorption, were compared to histology. Regions of increased terahertz absorption agreed well with the location of the tumor sites. Resolutions at 1 THz of 350 microm laterally and 40 microm axially in skin were attainable with our system. These results demonstrate the ability of terahertz pulse imaging to distinguish basal cell carcinoma from normal tissue, and this macroscopic technique may, in the future, help plan surgery.

Transvascular and interstitial transport of a 19 kDa linear molecule in human melanoma xenografts measured by contrast-enhanced magnetic resonance imaging

Cancer therapy involving blood-borne macromolecular therapeutic agents often fails, owing to inadequate macromolecule uptake in malignant tissue. The transvascular and interstitial transport of a 19 kDa linear molecule (NC22181 or poly-[Gd-DTPA]-co-[1,6-diaminohexane]) was studied in the present work in an attempt to identify transport barriers limiting the delivery of macromolecules to tumors. Tumors of four human melanoma xenograft lines were included in the study. The uptake of NC22181 was measured by spoiled gradient recalled magnetic resonance imaging (MRI). The effective microvascular permeability constant and the interstitial influx constant of NC22181 were calculated from NC22181 uptake curves by using a three-compartment tissue model. The uptake of NC22181 was limited by the interstitial transport and not by the transvascular transport in all xenograft lines. If the melanoma xenografts used in this study are representative models of human cancer, our results suggest that strategies for increasing the delivery of macromolecular therapeutic agents to tumors should focus on improving the transport conditions in the interstitium, rather than enhancing the permeability of the microvascular wall.

Microvascular permeability to macromolecules in human melanoma xenografts assessed by contrast-enhanced MRI--intertumor and intratumor heterogeneity

Several novel macromolecular anticancer agents have fallen short of expectations owing to inadequate and heterogeneous uptake in tumor tissue. In the present work, contrast-enhanced magnetic resonance imaging was used to measure the intertumor and intratumor heterogeneity in the effective microvascular permeability constant, P(eff), of an 82 kDa macromolecule in an attempt to identify possible causes of the inadequate and heterogeneous uptake. Tumors of two human melanoma xenograft lines (A-07 and R-18) were included in the study. Human serum albumin with 30 gadopentetate dimeglumine units per molecule was used as a model molecule of macromolecular therapeutic agents. P(eff) was measured in manually defined regions of interest, corresponding to a whole tumor (ROI(WHOLE)) or to subregions of a tumor (ROIs(SUB)). The P(eff) of the ROI(WHOLE) of individual tumors ranged from 1.4 x 10(-7) cm/s to 2.8 x 10(-7) cm/s (A-07) and from 7.7 x 10(-8) cm/s to 3.2 x 10(-7) cm/s (R-18). P(eff) decreased with increasing tumor volume in R-18, but was independent of tumor volume in A-07. The intratumor heterogeneity in P(eff) exceeded the intertumor heterogeneity in both tumor lines. Some ROIs(SUB) showed P(eff) values that were similar to or slightly higher than the P(eff) values of albumin in normal tissues. Our observations suggest that inadequate and heterogeneous uptake of macromolecular therapeutic agents in tumor tissue is partly a result of low and heterogeneous microvascular permeability. However, the microvascular wall is probably not the major transport barrier to macromolecules in A-07 and R-18 tumors, as most individual tumors and individual tumor subregions showed high P(eff) values, i.e. values that are up to 10-fold higher than those of normal tissues.

Antivascular treatment of solid melanoma tumors with bacteriochlorophyll-serine-based photodynamic therapy

We describe here a strategy for photodynamic eradication of solid melanoma tumors that is based on photo-induced vascular destruction. The suggested protocol relies on synchronizing illumination with maximal circulating drug concentration in the tumor vasculature attained within the first minute after administrating the sensitizer. This differs from conventional photodynamic therapy (PDT) of tumors where illumination coincides with a maximal concentration differential of sensitizer in favor of the tumor, relative to the normal surrounding tissue. This time window is often achieved after a delay (3-48 h) following sensitizer administration. We used a novel photosensitizer, bacteriochlorophyll-serine (Bchl-Ser), which is water soluble, highly toxic upon illumination in the near-infrared (lambda max 765-780 nm) and clears from the circulation in less than 24 h. Nude CD1 mice bearing malignant M2R melanotic melanoma xenografts (76-212 mm3) received a single complete treatment session. Massive vascular damage was already apparent 1 h after treatment. Changes in vascular permeability were observed in vivo using contrast-enhanced magnetic resonance imaging (MRI), with the contrast reagent Gd-DTPA, by shortening spin-spin relaxation time because of hemorrhage formation and by determination of vascular macromolecular leakage. Twenty-four hours after treatment a complete arrest of vascular perfusion was observed by Gd-DTPA-enhanced MRI. Histopathology performed at the same time confirmed primary vascular damage with occlusive thrombi, hemorrhage and tumor necrosis. The success rate of cure of over 80% with Bchl-Ser indicates the benefits of the short and effective treatment protocol. Combining the sensitizer administration and illumination steps into one treatment session (30 min) suggests a clear advantage for future PDT of solid tumors.

Intratumor heterogeneity in perfusion in human melanoma xenografts measured by contrast-enhanced magnetic resonance imaging

The perfusion in tumors shows substantial spatial heterogeneity compared to that in normal tissues. The aim of the present study was to evaluate the intratumor heterogeneity in perfusion in tumors of two amelanotic human melanoma xenograft lines, A-07 and R-18, grown intradermally in Balb/c nu/nu mice. A non-invasive contrast-enhanced magnetic resonance imaging method yielding results in absolute values was applied. The perfusion was determined in manually defined regions of interest, corresponding to a whole tumor or to subregions of a tumor. The mean perfusion and the intertumor heterogeneity in perfusion were similar for the two tumor lines. For whole A-07 tumors, the perfusion ranged from 0.089 mL/(g . min) to 0.20 mL/(g . min) [mean: 0.15 mL/(g . min)], and for whole R-18 tumors, from 0.030 mL/(g . min) to 0.17 mL/(g . min) [mean: 0.13 mL/(g . min)]. The intratumor heterogeneity, on the other hand, was estimated to be 6.4 times larger in A-07 tumors than in R-18 tumors. The highest perfusion values, up to 0.69 mL/(g . min), were found in subregions of A-07 tumors. The intratumor heterogeneity was substantially larger than the intertumor heterogeneity in A-07 tumors, whereas in R-18 tumors, the intratumor heterogeneity was similar to the intertumor heterogeneity. These observations imply that measurements of mean tumor perfusion may have limited value as a predictive assay for outcome of treatment.

Measurement of the extracellular volume of human melanoma xenografts by contrast enhanced magnetic resonance imaging

The magnitude of the extracellular volume fraction (ECV) of tumors is of importance for the transport of macromolecular therapeutic agents from the vessel wall to the tumor cells. The aim of this study was to develop a method for measurement of tumor ECV by contrast enhanced MRI. Tumors of two human amelanotic melanoma xenograft lines (A-07 and R-18) grown intradermally in Balb/c nu/nu mice were used as model system, and muscle tissue was used as control. The renal arteries of the mice were ligated prior to i.v. administration of Gd-DTPA, and an MRI protocol for calculating Gd-DTPA concentration in tissue was followed. ECV was calculated from the Gd-DTPA concentrations in the tissue and in a plasma sample. In muscle tissue, the concentration reached a constant level after 1 min and the ECV was calculated to be 0.12 (+/- 0.01), consistent with values reported in the literature. Individual tumors showed large differences in the uptake of Gd-DTPA. The Gd-DTPA concentration in the tissue at 40 min after the Gd-DTPA administration was used to calculate tumor ECV. The ECV was found to differ significantly among regions of individual tumors and among individual tumors. The ECV ranged from 0.075 to 0.33 for A-07 tumors and from 0.016 to 0.097 for R-18 tumors. The intra- and intertumor heterogeneity in ECV was confirmed by histologic findings, showing that contrast enhanced MRI is suitable for non-invasive studies of the ECV in experimental tumors without necrosis.

Utililization of experimental animal model for correlative multispectral MRI and pathological analysis of brain tumors

Magnetic resonance imaging is the method of choice for non-invasive detection and evaluation of tumors of the central nervous system. However, discrimination of tumor boundaries from normal tissue, and the evaluation of heterogeneous lesions have proven to be limitations in traditional magnetic resonance imaging. The use of post-image acquisition processing techniques, such as multispectral tissue segmentation analysis, may provide more accurate clinical information. In this report, we have employed an experimental animal model for brain tumors induced by glial cells transformed by the human neurotropic JC virus to examine the utility of multispectral tissue segmentation for tumor cell identification. Six individual tissue types were discriminated by segmentation analysis, including heterogeneous tumor tissue, a clear demarcation of the boundary between tumor and non-tumor tissue, deep and cortical gray matter, and cerebrospinal fluid. Furthermore, the segmentation analysis was confirmed by histopathological evaluation. The use of multispectral tissue segmentation analysis may optimize the non-invasive determination and volumetric analysis of CNS neoplasms, thus providing improved clinical evaluation of tumor growth and evaluation of the effectiveness of therapeutic treatments.

Measurement of proliferation activity in human melanoma xenografts by magnetic resonance imaging

Tumor proliferation may be predictive for malignant progression and response to fractionated therapy of cancer. The purpose of the present work was to investigate whether the proliferation activity of solid tumors can be assessed in vivo from the proton relaxation times, T1 and T2. Tumors of four amelanotic human melanoma xenograft lines were studied. Three parameters were used to represent tumor proliferation activity; the volume doubling time, Tvol, the potential doubling time, Tpot, and the fraction of cells in S-phase. Tvol was determined from volumetric growth data. Tpot and S-phase fraction were determined by flow cytometric analysis of tumor cells after bromodeoxyuridine (BrdU) incorporation in vivo. T1 and T2 were measured by 1H-MRI in vivo, using spin-echo pulse sequences. The proliferation parameters and relaxation times differed considerably among the tumor lines. Significant correlations were found between the proliferation parameters and the relaxation times, regardless of whether Tvol, Tpot, or S-phase fraction was considered. Tumors with short Tvol and Tpot and high S-phase fraction had long T1 and T2 compared to tumors with long Tvol and Tpot and low S-phase fraction. The elongated T1 and T2 of fast growing tumors were probably due to increased interstitial and/or intravascular water content. The present results suggest that in vivo spin-echo 1H-MRI can be used to discriminate between tumors of high and low proliferation activity.

Spin-spin relaxation times in myocardial hypertrophy induced by endocrine agents in rat

Magnetic resonance techniques afford a significant advantage for noninvasive diagnosis of cardiovascular pathology. The purpose of our present study was to assay the proton nuclear magnetic resonance (1H-NMR) sensitivity in the differential diagnosis of certain endocrine cardiovascular complications. In this context, we investigated the water state and content in the hypertrophied myocardium. Male and female Wistar rats were treated with different hormones (hydrocortisone acetate, testosterone, estradiol, thyroid hormones) in combination with isoproterenol (a synthetic catecholamine that induces myocardial ischemia and hypertrophy). The animals were sacrificed after 20 days of treatment and samples of integral myocardium and left ventricular myocardium were analyzed on a 1H-NMR AREMI spectrometer (0.6 T; proton resonance at 25 MHz). The estimation of T2 was made by Carr Purcell-Meiboom-Gill pulse sequence. The data were fitted to a bi-exponential curve, yielding short (T21) values for bound water and long (T22) values for free water. In order to evaluate the myocardial hypertrophy, the following ratios were calculated: integral myocardium to body weight; left ventricle to body weight; left ventricle to integral myocardium. The first two ratios were also calculated for dried tissue, in order to estimate its contribution to myocardial hypertrophy. Our findings demonstrate that myocardial hypertrophy is associated with a decrease of T22, as a consequence of the increase in the dried component (i.e. proteins) of the tissue, while the total tissue water (H2Ot%), measured by gravimetry) was not significantly modified. Nevertheless, it is reasonable that the increase in the protein content would be proportional with the increase in H2Ot%. The decrease of T21 seems to be proportional with the level of left ventricle hypertrophy in female groups. The 1H-NMR measurements were much sensitive for the differential diagnosis of myocardial hypertrophy in the case of left ventricle.