Functional CT imaging of the acute hyperemic response to radiation therapy of the prostate gland: early experience

Effect of Radiation on DCE-MRI Pharmacokinetic Parameters in a Rabbit Model of Compromised Maxillofacial Wound Healing: A Pilot Study

PURPOSE

Osteoradionecrosis (ORN), a potentially debilitating complication of maxillofacial radiation, continues to present a challenging clinical scenario, with limited treatment options that often fail. Translational animal models that can accurately mimic the human characteristics of the condition are lacking. In the present pilot study, we aimed to characterize the effects of radiation on the dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) pharmacokinetic parameters in a rabbit model of compromised maxillofacial wound healing to determine its potential as a translational model of ORN.

MATERIALS AND METHODS

An experimental group underwent fractionated radiation of the mandible totaling 36 Gy. At 4 weeks after irradiation, the experimental and control groups (n = 8 rabbits each) underwent a surgical procedure to create a critical size defect in the mandibular bone. DCE-MRI scans were acquired 1 week after arrival (baseline; time point 1), 4 weeks after completion of irradiation in the experimental group (just before surgery, time point 2), and 4 weeks after surgery (time point 3).

RESULTS

No differences in the analyzed DCE-MRI parameters were noted within the experimental or control group between the baseline values (time point 1) and those after irradiation (time point 2). The whole blood volume fraction (v_b) in the experimental group was increased compared with that in the control group after irradiation (time point 2; P < .05). After surgery (time point 3), both the forward flux rate of contrast from blood plasma and the extracellular extravascular space and the v_b were increased in the control group compared with the experimental group (P < .05).

CONCLUSIONS

The results of the present study suggest that DCE-MRI of a rabbit model of compromised maxillofacial wound healing could reflect the DCE-MRI characteristics of human patients with ORN and those at risk of developing the condition. Future studies will focus on further characterization of this rabbit model as a translational preclinical model of ORN.

Assessment of prostate cancer with integrated CT-perfusion using a sector-wise approach

OBJECTIVE

The role of computed tomography perfusion (CTP) in characterizing primary prostate cancer (PCa) is not definitely known. The aim of the present study was to investigate the relationship between CTP parameters and histopathological features of PCa tissue, using a sector-wise approach.

MATERIAL AND METHODS

Fifty-one patients with biopsy-proven PCa underwent prospectively a CTP scan prior to radical prostatectomy. Blood flow (BF), mean blood volume (BV) and mean transit time (MTT) were calculated, with the prostate being divided into eight sectors. Corresponding sector-wise histopathological analysis of whole-mount prostatectomy specimens was performed to determine tumoral area (mm²), mean microvessel density (MVD), Gleason patterns (primary, secondary) and total Gleason score. Spearman's rank correlation coefficient was used to analyze the association between CTP and histopathological parameters.

RESULTS

BF correlated weakly with tumoral area [ρs coefficient (p-value): 0.25 (0.00)] and MVD [ρs coefficient (p-value): 0.23 (0.00)]. No valuable correlation was found between CTP parameters and primary and secondary Gleason patterns, whereas total Gleason score was weakly correlated with BV [ρs coefficient (p-value): 0.22 (0.00)] and MTT [ρs coefficient (p-value): 0.25 (0.00)].

CONCLUSION

BF correlates weakly with size and vascularity of PCa. There is a need for further studies to elucidate the association between CTP parameters and other histopathological parameters.

Use of novel thermobrachytherapy seeds for realistic prostate seed implant treatments

PURPOSE

A practical means of delivering both therapeutic radiation and hyperthermia to a deep-seated target has been identified in the literature as highly desirable, provided it is capable of generating sufficient temperatures over the defined target volume. The authors present continued development of a dual-modality thermobrachytherapy (TB) seed, investigating its capabilities in delivering prescribed hyperthermia to realistic deep-seated targets.

METHODS

The TB seed is based on the ubiquitous low dose-rate (LDR) brachytherapy permanent implant. Heat is generated by incorporating a ferromagnetic core within the seed and placing the patient in an oscillating external magnetic field, producing eddy currents within the core and hence Joule heating. A strategically selected Curie temperature results in thermal self-regulation. The magnetic and thermal properties of the TB seed were studied experimentally by means of seed prototypes placed in a tissue-mimicking phantom and heated with an industrial induction heater, as well as computationally in the finite element analysis solver COMSOL Multiphysics. Patient-specific seed distributions derived from LDR permanent prostate implants previously conducted at their institution were modeled in COMSOL to evaluate their ability to adequately cover a defined target volume and to overcome the loss of heat due to blood perfusion within tissue. The calculated temperature distributions were analyzed by generating temperature-volume histograms, which were used to quantify coverage and temperature homogeneity for varied blood perfusion rates, seed Curie temperatures, and thermal power production rates. Use of additional hyperthermia-only (HT-only) seeds in unused spots within the implantation needles was investigated, as was an increase in these seeds' core size to increase their power. The impact of the interseed attenuation and scatter (ISA) effect on radiation dose distributions of this seed was also quantified by Monte Carlo studies in the software package Monte Carlo N-Particle Version 5.

RESULTS

Increasing the power production of the seeds, as well as increasing their Curie point, would increase the maximum blood perfusion rate that a given seed distribution could overcome to obtain an acceptable temperature distribution. However, this would also increase the maximum temperatures generated at the seed surfaces. Auxiliary HT-only seeds serve to improve the temperature uniformity within the target, as well as decrease the seed power generation requirements. Both an increase in their core size and an increase in both seed types' Curie temperatures enhance the resulting temperature coverage. The interseed and scatter effect caused by both the TB and HT-only seeds was found to reduce the dose to 90% of the target volume (D90) by a factor of 1.10 ± 0.02.

CONCLUSIONS

A systematic approach of combining LDR prostate brachytherapy with hyperthermia is described, and its ability to provide sufficient and uniform temperature distributions in realistic patient-specific implants evaluated. A combination of TB and HT-only seeds may be used to produce a uniform temperature distribution in a defined target. Various modeled changes to their design, such as optimization of their Curie temperature, improve their ability to overcome the thermal effects of blood perfusion. The enhanced ISA of the TB and HT-only seeds must be taken into account for dose calculations, but is manageable.

Improved accuracy of quantitative parameter estimates in dynamic contrast-enhanced CT study with low temporal resolution

PURPOSE

A previously proposed method to reduce radiation dose to patient in dynamic contrast-enhanced (DCE) CT is enhanced by principal component analysis (PCA) filtering which improves the signal-to-noise ratio (SNR) of time-concentration curves in the DCE-CT study. The efficacy of the combined method to maintain the accuracy of kinetic parameter estimates at low temporal resolution is investigated with pixel-by-pixel kinetic analysis of DCE-CT data.

METHODS

The method is based on DCE-CT scanning performed with low temporal resolution to reduce the radiation dose to the patient. The arterial input function (AIF) with high temporal resolution can be generated with a coarsely sampled AIF through a previously published method of AIF estimation. To increase the SNR of time-concentration curves (tissue curves), first, a region-of-interest is segmented into squares composed of 3 × 3 pixels in size. Subsequently, the PCA filtering combined with a fraction of residual information criterion is applied to all the segmented squares for further improvement of their SNRs. The proposed method was applied to each DCE-CT data set of a cohort of 14 patients at varying levels of down-sampling. The kinetic analyses using the modified Tofts' model and singular value decomposition method, then, were carried out for each of the down-sampling schemes between the intervals from 2 to 15 s. The results were compared with analyses done with the measured data in high temporal resolution (i.e., original scanning frequency) as the reference.

RESULTS

The patients' AIFs were estimated to high accuracy based on the 11 orthonormal bases of arterial impulse responses established in the previous paper. In addition, noise in the images was effectively reduced by using five principal components of the tissue curves for filtering. Kinetic analyses using the proposed method showed superior results compared to those with down-sampling alone; they were able to maintain the accuracy in the quantitative histogram parameters of volume transfer constant [standard deviation (SD), 98th percentile, and range], rate constant (SD), blood volume fraction (mean, SD, 98th percentile, and range), and blood flow (mean, SD, median, 98th percentile, and range) for sampling intervals between 10 and 15 s.

CONCLUSIONS

The proposed method of PCA filtering combined with the AIF estimation technique allows low frequency scanning for DCE-CT study to reduce patient radiation dose. The results indicate that the method is useful in pixel-by-pixel kinetic analysis of DCE-CT data for patients with cervical cancer.

Role of MR-DWI and MR-PWI in the radiotherapy of implanted pulmonary VX-2 carcinoma in rabbits

OBJECTIVE

To detect the activity of tumor cells and tumor blood flow before and after the radiotherapy of implanted pulmonary VX-2 carcinoma in rabbit models by using magnetic resonance diffusion-weighted imaging (MR-DWI) and magnetic resonance perfusion weighted imaging (MR-PWI), and to evaluate the effectiveness and safety of the radiotherapy based on the changes in the MR-DWI and MR-PWI parameters at different treatment stages.

METHODS

A total of 56 rabbit models with implanted pulmonary VX-2 carcinoma were established, and then equally divided into treatment group and control group. MR-DWI and MR-PWI were separately performed using a Philips Acheiva 1.5T MRI machine (Philips, Netherland). MRI image processing was performed using special perfusion software and the WORKSPACE advanced workstation for MRI. MR-DWI was applied for the observation of tumor signals and the measurement of apparent diffusion coefficient (ADC) values; whereas MR-PWI was used for the measurement of wash in rate (WIR), wash out rate (WOR), and maximum enhancement rate (MER). The radiation treatment was performed using Siemens PRIMUS linear accelerator. In the treatment group, the radiotherapy was performed 21 days later on a once weekly dosage of 1,000 cGy to yield a total dosage of 5,000 cGy.

RESULTS

THE ADC PARAMETERS IN THE REGION OF INTEREST ON DWI WERE AS FOLLOWS: on the treatment day for the implanted pulmonary VX-2 carcinoma, the t values at the center and the edge of the lesions were 1.352 and 1.461 in the treatment group and control group (P>0.05). During weeks 0-1 after treatment, the t values at the center and the edge of the lesions were 1.336 and 1.137 (P>0.05). During weeks 1-2, the t values were 1.731 and 1.736 (P<0.05). During weeks 2-3, the t values were 1.742 and 1.749 (P<0.05). During weeks 3-4, the t values were 2.050 and 2.127 (P<0.05). During weeks 4-5, the t values were 2.764 and 2.985 (P<0.05). The ADC values in the treatment group were significantly higher than in the control group. After the radiotherapy (5,000 cGy), the tumors remarkably shrank, along with low signal on DWI, decreased signal on ADC map, and remarkably increased ADC values. As shown on PWI, on the treatment day for the implanted pulmonary VX-2 carcinoma, the t values of the WIR, WOR, and MER at the center of the lesions were 1.05, 1.31, and 1.33 in the treatment group and control group (P>0.05); in addition, the t values of the WIR, WOR, and MER at the edge of the lesions were 1.35, 1.07, and 1.51 (P>0.05). During weeks 0-1 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 1.821, 1.856, and 1.931 (P<0.05); in addition, the t values of the WIR, WOR, and MER at the edge of the lesions were 1.799, 2.016, and 2.137 (P<0.05). During weeks 1-1 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.574, 2.156, and 2.059 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 1.869, 2.058, and 2.057 (P<0.05). During weeks 2-3 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.461, 2.098, and 2.739 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 2.951, 2.625, and 2.154 (P<0.05). During weeks 3-4 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.584, 2.107, and 2.869 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 2.057, 2.637, and 2.951 (P<0.05). During weeks 4-5 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.894, 2.827, and 3.285 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 3.45, 3.246, and 3.614 (P<0.05). After the radiotherapy (500 cGy), the tumors shrank on the T1WI, WIR, WOR, and MER; meanwhile, the PWI parameter gradually decreased and reached its minimum value.

CONCLUSIONS

MR-DWI and MR-PWI can accurately and directly reflect the inactivation of tumor cells and the tumor hemodynamics in rabbit models with implanted pulmonary VX-2 carcinoma, and thus provide theoretical evidences for judging the clinical effectiveness of radiotherapy for the squamous cell carcinoma of the lung.

Blood flow and oxygenation status of prostate cancers

Hypoxia is a characteristic of many solid tumors, can lead to the development of an aggressive phenotype and acquired treatment resistance, and is an independent, adverse prognostic indicator. In this literature review, we show that hypoxia is also a typical feature in prostate cancer (PC), the most commonly diagnosed cancer among men in most western countries. Data on blood flow (a major determinant of oxygenation status in malignancies) and on the oxygenation status (as assessed by O(2)-sensitive electrodes) are presented. Where possible, data on prostate cancers are compared to normal prostate (NP) tissue and benign prostate hyperplasia (BPH). The average blood flow rate in NP is 0.21 vs. 0.28 mL/g/min in BPH. Blood flow in PC is approximately three times higher than in NP (mean flow: 0.64 mL/g/min) and shows pronounced intra- and inter-tumor variability. Despite relatively high flow rates in PC, the overall mean pO(2) in cancers is 6 mmHg compared to 26 mmHg in NP. As was the case with blood flow, tissue oxygenation was extremely heterogeneous with no clear dependency on a series of tumor (Gleason score, clinical size, androgen deprivation) and patient characteristics (serum PSA levels, age).

Changes in apparent diffusion coefficient and T2 relaxation during radiotherapy for prostate cancer

PURPOSE

To evaluate regional and temporal changes in apparent diffusion coefficient (ADC) and T2 relaxation during radiation therapy (RT) in patients with low and intermediate risk localized prostate cancer.

MATERIALS AND METHODS

Seventeen patients enrolled on a prospective clinical trial where MRI was acquired every 2 weeks throughout eight weeks of image-guided prostate IMRT (78 Gy/39 fractions). ADC and T2 quantification used entire prostate, central gland, benign peripheral zone, and tumor-dense regions-of-interest, and mean values were evaluated for common response trends.

RESULTS

Overall, the RT responses were greater than volunteer measurement repeatability, and week 6 appeared to be an optimum time-point for early detection. RT effects on the entire prostate were best detected using ADC (5-7% by week 2, P < 0.0125), effects on peripheral zone were best detected using T2 (19% reduction at week 6; P = 0.004) and effects on tumors were best detected using ADC (14% elevation at week 6; P = 0.004).

CONCLUSION

ADC and T2 may be candidate biomarkers of early response to RT warranting further investigation against clinical outcomes.

Does computed tomography or positron emission tomography/computed tomography contribute to detection of small focal cancers in the prostate?

Prostate cancer is considered to be a multifocal tumor in the majority of patients. Based on histologic data after prostatectomy, there is a growing insight that a considerable number of men who receive a diagnosis in the contemporary setting of prostate-specific antigen screening have unilateral or unifocal disease. With this, the current concept of whole-gland therapy has come into discussion. The need for improvement of intraprostatic tumor characterization is clear. Molecular imaging is one of the areas of research on this aspect. The clinical indications for positron emission tomography (PET)/CT have increased rapidly in the field of oncology and are largely based on fluorodeoxyglucose (FDG) PET. Both conventional CT and FDG PET, however, cannot detect prostate cancer foci <5 mm within the prostate. Dynamic contrast-enhanced CT involves imaging a region of interest rapidly (usually <10 seconds between images) during a bolus intravenous injection of a contrast agent. Through analysis of the contrast enhancement time curves, it is possible to distinguish tissues with different microvascular properties such as cancer. The technologic aspects of both imaging techniques and the clinical results of 11C-choline PET/CT for intraprostatic tumor characterization are discussed. Based on preliminary studies, dynamic contrast-enhanced (DCE)-CT may be a useful tool for localization of prostate tumors and, perhaps more importantly, quantification of therapeutic response in prostate cancer. Validation work is necessary, however, to define its accuracy and role in therapeutic paradigms such as focal therapies, particularly given the current accuracy of MRI. In the future, combining DCE-CT with CT or (11)C-choline PET/CT may be an alternative to MRI, offering a combination of quantitative parameters that may correlate to tumor prognosis as well as cancer localization for focal therapy.

Imaging angiogenesis of genitourinary tumors

Angiogenesis is a key process in the growth and metastasis of cancer, and genitourinary tumors are no exception. The evolution of angiogenesis as an important target for novel anticancer therapeutics has brought with it new challenges for in vivo imaging. Most imaging techniques quantify physiological parameters, such as blood volume and capillary endothelial permeability. Although CT, PET and ultrasonography have shown promise, MRI is the most common method used to evaluate angiogenesis in clinical trials of genitourinary tumors. Pilot studies of MRI, CT and ultrasonography in patients with renal cancer have produced promising results; reductions in vascular permeability and blood flow have been correlated with progression-free survival. The vascular characteristics of prostate cancer have been evaluated by MRI, and this has been suggested as a means of assessing tumor response to hormone deprivation therapy. Current evidence highlights the potential of angiogenesis imaging in the diagnosis, staging and possibly response monitoring of bladder cancer. In the future, assessment of the angiogenic process at the structural, functional and molecular levels, before, during and after antiangiogenic therapy will undoubtedly be integrated into wider clinical practice.

MRI before and after external beam intensity-modulated radiotherapy of patients with prostate cancer: the feasibility of monitoring of radiation-induced tissue changes using a dynamic contrast-enhanced inversion-prepared dual-contrast gradient echo sequence

PURPOSE

To identify and quantify suitable pharmacokinetic MRI parameters for monitoring tissue changes after external beam intensity-modulated radiotherapy of prostate cancer.

MATERIAL AND METHODS

Six patients with biopsy-proven prostate cancer (initial PSA, 6.0-81.4 ng/ml) underwent MRI at 1.5 T using a combined endorectal/body phased-array coil and a dynamic contrast-enhanced inversion-prepared dual-contrast gradient echo sequence (T1/T2(*)w; 1.65 s temporal resolution). MRI was performed before and immediately after radiotherapy, at 3 months and at 1 year. Perfusion, blood volume, mean transit time, delay, dispersion, interstitial volume, and extraction coefficient were calculated in prostate cancer and normal prostate for all four time points using a sequential 3-compartment model.

RESULTS

Prostate cancer and normal prostate tissue showed a statistically significant decrease in perfusion (p=0.006, p=0.001) and increase in extraction coefficient (p=0.004, p<0.001). For prostate cancer, there was also a decrease in vascular volume (p=0.034). The other parameters investigated showed no statistically significant changes. Statistically significant differences between prostate cancer and normal prostate tissue were only observed before radiotherapy, when prostate cancer showed significantly higher perfusion (1.84 vs. 0.12 ml/cm(3)min, p=0.028) and a smaller extraction coefficient (0.42 vs. 0.64, p=0.028).

CONCLUSIONS

Two pharmacokinetic parameters, perfusion and extraction coefficient, appear to be suitable candidates for monitoring the response to percutaneous intensity-modulated radiotherapy of prostate cancer.

Advanced gastric cancer and perfusion imaging using a multidetector row computed tomography: correlation with prognostic determinants

Objective

To investigate the relationship between the perfusion CT features and the clinicopathologically determined prognostic factors in advanced gastric cancer cases.

Materials and Methods

A perfusion CT was performed on 31 patients with gastric cancer one week before surgery using a 16-channel multi-detector CT (MDCT) instrument. The data were analyzed with commercially available software to calculate tumor blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface (PS). The microvessel density (MVD), was evaluated by immunohistochemical staining of the surgical specimens with anti- CD34. All of the findings were analyzed prospectively and correlated with the clinicopathological findings, which included histological grading, presence of lymph node metastasis, serosal involvement, distant metastasis, tumor, node, metastasis (TNM) staging, and MVD. The statistical analyses used included the Student's t-test and the Spearman rank correlation were performed in SPSS 11.5.

Results

The mean perfusion values and MVD for tumors were as follows: BF (48.14±16.46 ml/100 g/min), BV (6.70±2.95 ml/100 g), MTT (11.75±4.02 s), PS (14.17±5.23 ml/100 g/min) and MVD (41.7±11.53). Moreover, a significant difference in the PS values was found between patients with or without lymphatic involvement (p = 0.038), as well as with different histological grades (p = 0.04) and TNM stagings (p = 0.026). However, BF, BV, MTT, and MVD of gastric cancer revealed no significant relationship with the clinicopathological findings described above (p > 0.05).

Conclusion

The perfusion CT values of the permeable surface could serve as a useful prognostic indicator in patients with advanced gastric cancer.

Imaging techniques to evaluate the response to treatment in oncology: current standards and perspectives

Response evaluation in solid tumours currently uses radiological imaging techniques to measure changes under treatment. Imaging requires a well-defined anatomical lesion to be viewed and relies on the measurement of a reduction in tumour size during treatment as the basis for presumed clinical benefit. However, with the development of anti-angiogenesis agents, anatomical imaging has became inappropriate as certain tumours would not reduce in size. Functional studies are therefore necessary and dynamic contrast enhanced magnetic resonance imaging (DCE-MRI), DCE-computed tomography (CT) and DCE-ultrasonography (US) are currently being evaluated for monitoring treatments. Diffusion-weighted MR imaging (DW-MRI) and magnetic resonance spectroscopy (MRS) are also capable of detecting changes in cell density and metabolite content within tumours. In this article, we review anatomical and functional criteria currently used for monitoring therapy. We review the published data on DCE-MRI, DCE-CT, DCE-US, DW-MRI and MRS. This literature review covers the following area: basic principles of the technique, clinical studies, reproducibility and repeatability, limits and perspectives in monitoring therapy. Anatomical criteria such as response evaluation criteria in solid tumours (RECIST) will require adaptation to employ not only new tools but also different complementary techniques such as functional imaging in order to monitor therapeutic effects of conventional and new anti-cancer agents.

Influence of perfusion on high-intensity focused ultrasound prostate ablation: a first-pass MRI study

Our aim was to evaluate the influence of regional prostate blood flow (rPBF) on high-intensity focused ultrasound (HIFU) treatment outcome. A total of 48 patients with clinically localized prostate cancer were examined by dynamic contrast-enhanced (DCE)-MRI prior to HIFU therapy. A prostate-specific antigen (PSA) nadir threshold of 0.2 ng/ml was used to define the populations of responders and nonresponders. A dedicated tracer kinetic model, namely "monoexponential plus constant" (MPC) deconvolution, was implemented to provide quantitative estimates of rPBF. The results were compared with those obtained by semiquantitative (steepest slope, mean gradient) and quantitative (Fermi deconvolution) approaches. Of the four methods studied, quantitative rPBF obtained by MPC deconvolution proved the most sensitive to the perfusion changes encountered in this study. Furthermore, blood-flow values obtained with MPC deconvolution in the prostate and muscle (12 +/- 8 and 5 +/- 3 ml/min/100 g, respectively) were in good agreement with literature data. The mean pretreatment rPBF obtained with MPC deconvolution was significantly higher in nonresponders compared to responders (16 +/- 9 vs. 10 +/- 6 ml/min/100 g), suggesting a correlation between baseline perfusion and treatment outcome. The present work describes and validates the use of dynamic MRI to estimate rPBF in patients, which in the future may help to refine the conduct of HIFU therapy.

Dynamic contrast enhanced MRI in prostate cancer

Angiogenesis is an integral part of benign prostatic hyperplasia (BPH), is associated with prostatic intraepithelial neoplasia (PIN) and is key to the growth and for metastasis of prostate cancer. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) using small molecular weight gadolinium chelates enables non-invasive imaging characterization of tissue vascularity. Depending on the technique used, data reflecting tissue perfusion, microvessel permeability surface area product, and extracellular leakage space can be obtained. Two dynamic MRI techniques (T2*-weighted or susceptibility based and T1-weighted or relaxivity enhanced methods) for prostate gland evaluations are discussed in this review with reference to biological basis of observations, data acquisition and analysis methods, technical limitations and validation. Established clinical roles of T1-weighted imaging evaluations will be discussed including lesion detection and localisation, for tumour staging and for the detection of suspected tumour recurrence. Limitations include inadequate lesion characterisation particularly differentiating prostatitis from cancer, and in distinguishing between BPH and central gland tumours.

Imaging tumor angiogenesis: functional assessment using MDCT or MRI?

Functional imaging using multidetector row computed tomography and dynamic contrast-enhanced magnetic resonance imaging are increasingly advocated for assessment of tumor vascularity because these techniques provide excellent anatomic imaging and reliable quantitative perfusion data and are easily incorporated into routine examinations. However, differences in acquisition techniques, mathematical analysis, measurement parameters, and propensity to artifacts influence the choice of imaging modality, which is explored in this review.

Feasibility and measurement precision of 3D quantitative blood flow mapping of the prostate using dynamic contrast-enhanced multi-slice CT

We have developed a 3D dynamic contrast-enhanced (DCE) multislice CT protocol that covers the complete prostate. The DCE-CT data are subsequently analysed using the adiabatic approximation of the tissue homogeneity model resulting in five 3D quantitative maps of blood flow, mean transit time, extraction fraction, extracellular extravascular space and delay time. The purpose of this study was to establish the feasibility of determining these parameters in the prostate with a spatial resolution as high as approximately 0.1 cc as well as a good measurement precision. The precision of the parameter estimation as a function of noise level is determined by a Monte Carlo-based method that simulates the effect of noise present in the data. We find that the precision depends on the value of the flow and transit time, where a higher value is favourable. At a noise level of 4 HU in combination with a peak enhancement in the iliac arteries of approximately 300 HU the 95% confidence intervals are sufficiently small to discriminate whether a parameter value is above or below a given threshold. We have collected and analysed the noise level in the DCE-data of five patients. A noise level of 3.8 HU on average can be obtained by averaging to a voxel volume of 4.5 x 4.5 x 5 mm(3) = 0.1 cc. Analysis of the parameter maps shows that it is feasible to detect both small and large lesions, as well as irregularly shaped lesions.

Imaging vascular physiology to monitor cancer treatment

The primary physiological function of the vasculature is to support perfusion, the nutritive flow of blood through the tissues. Vascular physiology can be studied non-invasively in human subjects using imaging methods such as positron emission tomography (PET), magnetic resonance imaging (MRI), X-ray computed tomography (CT), and Doppler ultrasound (DU). We describe the physiological rationale for imaging vascular physiology with these methods. We review the published data on repeatability. We review the literature on 'before-and-after' studies using these methods to monitor response to treatment in human subjects, in five broad clinical settings: (1) antiangiogenic agents, (2) vascular disruptive agents, (3) conventional cytotoxic drugs, (4) radiation treatment, and (5) agents affecting drug delivery. We argue that imaging of vascular physiology offers an attractive 'functional endpoint' for clinical trials of anticancer treatment. More conventional measures of tumour response, such as size criteria and the uptake of fluorodeoxyglucose, may be insensitive to therapeutically important changes in vascular function.

Angiogenesis imaging in the management of prostate cancer

Angiogenesis is an integral part of benign prostatic hyperplasia, is associated with prostatic intraepithelial neoplasia and is a key factor in the growth and metastasis of prostate cancer. This review focuses on ultrasound and dynamic MRI in the evaluation of prostate cancer angiogenesis, and compares these techniques to functional CT and hydrogen magnetic resonance spectroscopic imaging. Image-based evaluation of angiogenesis in the prostate has established clinical roles in lesion detection, tumor staging and the detection of suspected tumor recurrence. One limitation of all these imaging techniques, however, is inadequate lesion characterization, particularly in differentiating prostatitis from cancer in the peripheral zone of the prostate, and in distinguishing between benign prostatic hyperplasia and central-gland tumors. Ultimately, local availability, expertise and the need to minimize patients' radiation burden will influence which technique is used in prostatic evaluations.

Quantitative colorectal cancer perfusion measurement using dynamic contrast-enhanced multidetector-row computed tomography: effect of acquisition time and implications for protocols

OBJECTIVE

To determine the effect of acquisition time on quantitative colorectal cancer perfusion measurement.

METHODS

Dynamic contrast-enhanced computed tomography (CT) was performed prospectively in 10 patients with histologically proven colorectal cancer using 4-detector row CT (Lightspeed Plus; GE Healthcare Technologies, Waukesha, WI). Tumor blood flow, blood volume, mean transit time, and permeability were assessed for 3 acquisition times (45, 65, and 130 seconds). Mean values for all 4 perfusion parameters for each acquisition time were compared using the paired t test.

RESULTS

Significant differences in permeability values were noted between acquisitions of 45 seconds and 65 and 130 seconds, respectively (P=0.02, P=0.007). There was no significant difference for values of blood volume, blood flow, and mean transit time between any of the acquisition times.

CONCLUSIONS

Scan acquisitions of 45 seconds are too short for reliable permeability measurement in the abdomen. Longer acquisition times are required.

Contrast-enhanced computed tomography and ultrasound for the evaluation of tumor blood flow

OBJECTIVE

We evaluated implanted rat mammary adenocarcinoma tumors during a 5-week period using ultrasound, computed tomography (CT), and histology.

MATERIALS AND METHODS

Contrast-enhanced ultrasound with a destruction-replenishment imaging scheme was used to derive estimates of blood volume and flow. These ultrasound-derived measures of microvascular physiology were compared with contrast-enhanced CT-derived measures of perfusion and vascular volume made by the Mullani-Gould formula and Patlak analysis, respectively.

RESULTS

The tumor cross-sectional area and necrotic core cross-sectional area determined by the 3 methods were correlated (r>0.8, P<0.001, n=15). The spatial integral of perfusion estimated by CT correlated with the spatial integral of flow from ultrasound (P<0.05). The contrast-enhanced tumor area calculated from the ultrasound analysis was highly correlated with the contrast-enhanced area estimated by CT images (r=0.89, P<0.001, n=15). However, the fraction of the tumor area enhanced by the CT contrast agent was significantly larger than either the fraction enhanced by ultrasound contrast agent or than the viable area as estimated from histology slides.

CONCLUSION

Destruction-replenishment ultrasound provides valuable information about the spatial distribution of blood flow and vascular volume in tumors and ultrasound analysis compares favorably with a validated contrast-enhanced CT method.

Perfusion CT for the assessment of tumour vascularity: which protocol?

Perfusion CT is a technique that can be readily incorporated into the existing CT protocols that continue to provide the mainstay for anatomical imaging in oncology to provide an in vivo marker of tumour angiogenesis. By capturing physiological information reflecting the tumour vasculature, perfusion CT can be useful for diagnosis, risk-stratification and therapeutic monitoring. However, a wide range of perfusion CT techniques have evolved and the various commercial implementations advocate different acquisition protocols and processing methods. Acquisition choices include first pass studies or delayed imaging, temporal resolution versus image noise, and single location sequences or multiple spiral acquisitions. Data processing may be semi-quantitative or, using either compartmental analysis or deconvolution, produce results that are quantified in absolute physiological terms such as perfusion, blood volume and permeability. This article discusses the advantages and disadvantages of the more common CT perfusion protocols and offers proposals that could allow for easier comparison between studies employing different techniques.

Prostate Cancer: Evaluation of Vascular Characteristics with Dynamic Contrast-enhanced T1-weighted MR Imaging—Initial Experience

PURPOSE

To use contrast material-enhanced magnetic resonance (MR) imaging and a distributed-parameter tracer kinetics model for prospectively evaluating the vascular characteristics of prostate cancer.

MATERIALS AND METHODS

Twenty-two patients between 57 and 76 years of age (mean age, 67 years) with histologically proved adenocarcinoma of the prostate were examined by using three-dimensional dynamic contrast-enhanced T1-weighted MR imaging at 1.5 T. The local research ethics committee approved this study, and written consent was obtained from all patients. Data from regions of interest drawn in tumor, normal-appearing peripheral zone tissue, and muscle were analyzed to provide estimates of perfusion, blood volume, interstitial volume, and microvascular permeability-surface area product. These estimates were compared by using the nonparametric Wilcoxon signed rank test.

RESULTS

Mean blood flow was significantly (P < .001) higher in 22 prostate tumors than in 20 contralateral peripheral zones (66 vs 32 mL/100 mL/min). Similarly, the interstitial distribution volume in tumors was enlarged compared with the interstitial distribution volume in normal peripheral zones (42 vs 27 mL/100 mL). Blood volume and microvascular permeability-surface area product values in tumors (1.0 mL/100 mL and 22 mL/100 mL/min, respectively) were similar to estimated values in peripheral zone tissue (1.5 mL/100 mL and 21 mL/100 mL/min, respectively).

CONCLUSION

These findings show considerable promise for isolating vascular characteristics of prostate cancer.

Can color doppler predict the uniformity of HIFU-induced prostate tissue destruction?

BACKGROUND

Tissue blood perfusion influences the results of some hyperthermia and thermotherapy procedures, but its role in the outcome of prostate cancer treatment by high-intensity focused ultrasound (HIFU) has not been evaluated yet. We evaluated preoperative prostate color Doppler as a predictor of the efficacy of HIFU treatment.

METHODS

Thirty-five patients underwent pre- and post-contrast color Doppler examination of the prostate before HIFU treatment. Specific software was used to calculate, on color Doppler images, the color pixel density (CPD), and the specific flow (SF, i.e., mean velocity x CPD) in different regions of interest. Post-treatment sextant biopsies were obtained in 31 patients, 5.8 +/- 2.8 months after HIFU treatment.

RESULTS

No significant correlation was found between the uniformity of HIFU-induced tissue destruction observed on control biopsies and the pre-treatment CPD/SF values in any region of interest, either before or after contrast injection. On the other hand, history of radiation therapy was significantly associated with homogeneous tissue destruction and history of hormone therapy was significantly associated with incomplete tissue destruction.

CONCLUSIONS

Color Doppler cannot predict the uniformity of HIFU-induced tissue destruction. History of radiation therapy was found to be a factor of favorable prognosis and history of hormone therapy was found to be a factor of poor prognosis in our population.

Functional CT imaging in oncology

The two-compartment pharmacokinetics exhibited by iodinated contrast media makes these agents well suited to the study of tumour angiogenesis in which new vessels are not only produced in greater number but also are abnormally permeable to circulating molecules. The temporal changes in contrast enhancement of tumours on CT have been shown to correlate with histopathological assessments of angiogenesis with the intravascular and extravascular phases of contrast enhancement reflecting microvessel density and vascular permeability, respectively. By quantifying tumour contrast enhancement to capture physiological information about the vascular system, functional CT can provide a useful adjunct to the anatomical information afforded by MDCT in oncology, aiding with tumour diagnosis, risk stratification and therapy monitoring. By simultaneously assessing tumour vascularity and metabolic demand, the broader expansion of integrated MDCT/PET imaging will support highly sophisticated assessments of tumour biology within a single examination.

Quantitative Evaluation of Perfusion and Permeability of Peripheral Tumors Using Contrast-Enhanced Computed Tomography

RATIONALE AND OBJECTIVES

Our purpose was to validate contrast-enhanced computed tomography (CECT)-derived quantitative measures of perfusion and permeability against gold standard techniques of fluorescent microspheres and Evan's Blue dye, respectively.

MATERIALS AND METHODS

Normal and tumor-bearing (R3230AC) Fischer 344 rats were used. CECT perfusion measurements of normal and tumor tissue were compared with quantitative fluorescent microsphere perfusion measures. CECT permeability measurements from tumors were compared with semiquantitative Evan's Blue Dye permeability estimates. CT images were obtained precontrast and an imaging plane was selected. Serial, stationary images were obtained every 2 seconds for 2 minutes after intravenous bolus of iodinated contrast. Permeability and perfusion were measured by applying Patlak analysis to time-density data from normal tissue or tumor and femoral artery.

RESULTS

There was good correlation between fluorescent microsphere and CECT measurements of perfusion (r2 = 0.681, P << 0.001) and between Evan's Blue Dye and CECT measurements of permeability (r2 = 0.873, P = 0.0007).

CONCLUSIONS

CECT provides useful, quantifiable measures of perfusion and permeability in peripheral tumors.

Quantitative perfusion map of malignant liver tumors, created from dynamic computed tomography data

RATIONALE AND OBJECTIVES

To apply perfusion computed tomography (CT) technique to variable malignant liver tumors, and to define the usefulness of quantitative color mapping.

MATERIALS AND METHODS

Perfusion CT images were created for 36 malignant liver tumors in 28 patients (age, 66.4 +/- 10.1 years; range, 48-85) with metastatic liver tumors (n = 17; nine colorectal carcinomas, eight other malignant tumors) and hepatocellular carcinomas (n = 11). A single-slice dynamic CT was performed after an intravenous bolus injection of 40 mL of contrast material (320 mgI/mL) with 8 mL/sec. The parameters were calculated pixel-by-pixel using maximum slope method, and quantitative maps of arterial and portal perfusion were created. In four patients who underwent transcatheter arterial chemoembolization, perfusion CT was performed before and after transcatheter arterial chemoembolization.

RESULTS

In all patients, liver tumors were shown as hypervascular lesions on arterial perfusion CT. The average arterial perfusion value of the metastatic tumors from the colorectal carcinomas was 0.67 +/- 0.33 mL/min/mL, and that of hepatocellular carcinomas was 0.94 +/- 0.26 mL/min/mL (P = .03). The other metastatic tumors from various primary tumors showed a wide range (0.19-1.45 mL/min/mL) of arterial perfusion. Arterial perfusion of the liver tumors was obviously decreased after successful transcatheter arterial chemoembolization. In 12 of 15 tumors, in which portal perfusion CT images could be created, region-of-interest analysis showed no portal perfusion in the tumors. In two cases, decreased portal perfusion in the segments, which malignant tumors involved, was demonstrated.

CONCLUSION

Perfusion CT can provide quantitative information about arterial and portal perfusion of liver tumors, combined with good anatomic detail in one image. This technique has a potential to evaluate the angiogenesis of liver tumors, to show secondary changes in perfusion, such as decreased portal perfusion in apparently normal liver adjacent to metastases, and to monitor the therapeutic response in vivo.

Functional CT imaging of prostate cancer

The purpose of this paper is to investigate the distribution of blood flow (F), mean capillary transit time (Tc), capillary permeability (PS) and blood volume (vb) in prostate cancer using contrast-enhanced CT. Nine stage T2-T3 prostate cancer patients were enrolled in the study. Following bolus injection of a contrast agent, a time series of CT images of the prostate was acquired. Functional maps showing the distribution of F, Tc, PS and vb within the prostate were generated using a distributed parameter tracer kinetic model, the adiabatic approximation to the tissue homogeneity model. The precision of the maps was assessed using covariance matrix analysis. Finally, maps were compared to the findings of standard clinical investigations. Eight of the functional maps demonstrated regions of increased F, PS and vb, the locations of which were consistent with the results of standard clinical investigations. However, model parameters other than F could only be measured precisely within regions of high F. In conclusion functional CT images of cancer-containing prostate glands demonstrate regions of elevated F, PS and Vb. However, caution should be used when applying a complex tracer kinetic model to the study of prostate cancer since not all parameters can be measured precisely in all areas.

Contrast-assisted destruction-replenishment ultrasound for the assessment of tumor microvasculature in a rat model

Angiogenesis, the development of new blood vessels, is necessary for tumor growth. Anti-angiogenic therapies have recently received attention as a possible cancer treatment. The purpose of this study was to monitor the vascularity of induced tumors in rats using contrast-enhanced ultrasound during anti-angiogenic therapy. Six rats with subcutaneously implanted R3230 murine mammary adenocarcinomas were treated with an orally administered anti-angiogenic agent (SU11657) beginning 28 days after tumor implantation (20 mg/kg BW once daily). Three additional tumor-bearing control rats were treated with an equivalent volume of vehicle alone. Sonographic evaluation of tumor blood flow was performed using a modified Siemens Sonoline Elegra equipped with a 5.0 MHz linear transducer prior to drug administration, during the first 51 hours following initial drug administration, and on days 8 and 15 after initiation of therapy. Tumor volumes were estimated at each time point using a prolate ellipsoid method from linear dimensions measured on the B-mode ultrasound image in the three major axes. A destruction-replenishment technique was used for tumor blood flow evaluation using a constant rate infusion of intravenously delivered ultrasound contrast media (Definity). A destructive pulse was fired first, followed by a chain of non-destructive pulses that allowed for visualization of vascular contrast agent replenishment. Parametric maps of the time required for contrast agent replenishment and the time-integrated intensity were generated for both the tumor and kidney. Following ultrasound examination, contrast-enhanced computed tomography of each tumor was performed in the same imaging plane as that used to acquire the ultrasound images. Fifteen days after the start of treatment, tumors were excised, preserved in 10% formalin, and sectioned in a plane approximating the ultrasound and CT imaging planes. Sections were prepared for light microscopy with H & E, CD31 and factor VIII immunostain to evaluate overall morphology and vessel distribution. Ultrasound measurements of tumor volume, the spatial extent of contrast enhancement, and the time required for contrast replenishment within control tumors were significantly different from those of treated tumors. The time-integrated ultrasound contrast enhancement decreases and the time required for replenishment of the contrast agent within the tumor volume increases over the course of anti-angiogenic therapy. Parametric maps of integrated intensity are shown to correlate with the regions of viable tumor demonstrated on H & E and regions of elevated contrast intensity on CT. Contrast-enhanced ultrasound imaging of implanted tumors provides a tool to assess differences in the microcirculation of treated and control tumors in studies of anti-angiogenic agents.

Functional computed tomography in oncology

Functional Computed Tomography (CT) describes the use of existing technologies and conventional contrast agents to capture physiological parameters that reflect the vasculature within tumours and other tissues. The technique is readily incorporated into routine conventional CT examinations and, in tumours, the physiological parameters obtained provide an in-vivo marker of angiogenesis. As well as providing a research tool, functional CT has clinical applications in tumour diagnosis, staging, risk stratification and therapy monitoring, including the characterisation of pulmonary nodules, detection of occult hepatic metastases, grading of cerebral glioma and monitoring of anti-angiogenesis drugs. With the recent commercial availability of appropriate software and the development of multislice CT systems, functional CT is poised to make a significant impact upon the imaging of patients with cancer.

Prostate perfusion in patients with locally advanced prostate carcinoma treated with different hyperthermia techniques

PURPOSE

We determined prostate perfusion in 18 patients with locally advanced prostate carcinoma treated with a combination of external beam irradiation and regional (10) or interstitial (8) hyperthermia.

MATERIALS AND METHODS

Perfusion values were calculated from temperature elevations due to constant applied power and from transient temperature measurements after a change in applied power. Student's t test was used for comparing perfusion values with time and in the 2 groups.

RESULTS

At the start of regional hyperthermia treatment mean estimated perfusion plus or minus standard deviation was 10 +/- 8 ml./100 gm. per minute. At the end of treatment mean perfusion was increased to 14 +/- 2 ml./100 gm. per minute (p <0.01). Achieved thermal parameters were a mean temperature of at least 40.3C +/- 0.6C in 90% of the prostate, 40.9C +/- 0.6C in 50% and a mean maximum temperature of 41.6C +/- 0.6C. At the end of interstitial hyperthermia treatment estimated mean perfusion was 47 +/- 5 ml./100 gm. per minute, which was significantly different compared with the end of regional hyperthermia (p < 0(-7) ). Mean temperature was at least 39.4C +/- 0.9C in 90% of the prostate and 41.8C +/- 1.6C in 50%, while mean maximum temperature was 53.1C +/- 6.3C. Systemic temperature increased during regional hyperthermia up to 38.6C, whereas during interstitial hyperthermia body temperature was not elevated.

CONCLUSIONS

During interstitial hyperthermia perfusion values are higher than during regional hyperthermia. Hyperthermia causes increased prostate perfusion.