Glucose Metabolism of Human Prostate Cancer Mouse Xenografts

Dual-Tracer PET-Computed Tomography Imaging for Precision Radio-Molecular Theranostics of Prostate Cancer: A Futuristic Perspective

Dual/multi-tracer PET-computed tomography (CT) scan has been an interesting and intriguing concept and is promising in noninvasive and overall characterization of tumor biology and heterogeneity and has scientifically augmented the practice of precision oncology. In prostate carcinoma, particularly in metastatic castration-resistant prostate carcinoma setting, dual-tracer PET-CT can be potentially useful in selecting patients for chemotherapy, androgen deprivation therapy or prostate-specific membrane antigen (PSMA)-based peptide receptor radioligand therapy either as mono-therapy or as combination therapy, ascertaining differentiation status, staging/restaging, prognostication, and predicting progression/response. PSMA PET/CT has great potential as a "rule out" test in baseline staging, while being very useful in restaging and metastatic workup.

Molecular Imaging Assessment of Androgen Deprivation Therapy in Prostate Cancer

Hormonal therapy has long been recognized as a mainstay treatment for prostate cancer. New generation imaging agents have provided unprecedented opportunities at all phases along the natural history of prostate cancer. We review the literature on the effect of androgens and androgen deprivation therapy on prostate tumor at its various biological phases using the new generation molecular imaging agents in conjunction with positron emission tomography.

Beyond the Prognostic Value of 2-[18F]FDG PET/CT in Prostate Cancer: A Case Series and Literature Review Focusing on the Diagnostic Value and Impact on Patient Management

The role of 2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography/Computed Tomography (FDG PET/CT) in the management of prostate cancer (PCa) patients is increasingly recognised. However, its clinical role is still controversial. Many published studies showed that FDG PET/CT might have a prognostic value in the metastatic castration-resistant phase of the disease, but its role in other settings of PCa and, more importantly, its impact on final clinical management remains to be further investigated. We describe a series of six representative clinical cases of PCa in different clinical settings, but all characterised by a measurable clinical impact of FDG PET/CT on the patients' management. Starting from their clinical history, we report a concise narrative literature review on the advantages and limitations of FDG PET/CT beyond its prognostic value in PCa. What emerges is that in selected cases, this imaging technique may represent a useful tool in managing PCa patients. However, in the absence of dedicated studies to define the optimal clinical setting of its application, no standard recommendations on its use in PCa patients can be made.

The Utility of [18F]DASA-23 for Molecular Imaging of Prostate Cancer with Positron Emission Tomography

PURPOSE

There is a strong, unmet need for superior positron emission tomography (PET) imaging agents that are able to measure biochemical processes specific to prostate cancer. Pyruvate kinase M2 (PKM2) catalyzes the concluding step in glycolysis and is a key regulator of tumor growth and metabolism. Elevation of PKM2 expression was detected in Gleason 8-10 tumors compared to Gleason 6-7 carcinomas, indicating that PKM2 may potentially be a marker of aggressive prostate cancer. We have recently reported the development of a PKM2-specific radiopharmaceutical [18F]DASA-23 and herein describe its evaluation in cell culture and preclinical models of prostate cancer.

PROCEDURE

The cellular uptake of [18F]DASA-23 was evaluated in a panel of prostate cancer cell lines and compared to that of [18F]FDG. The specificity of [18F]DASA-23 to measure PKM2 levels in cell culture was additionally confirmed through the use of PKM2-specific siRNA. PET imaging studies were then completed utilizing subcutaneous prostate cancer xenografts using either PC3 or DU145 cells in mice.

RESULTS

[18F]DASA-23 uptake values over 60-min incubation period in PC3, LnCAP, and DU145 respectively were 23.4 ± 4.5, 18.0 ± 2.1, and 53.1 ± 4.6 % tracer/mg protein. Transient reduction in PKM2 protein expression with siRNA resulted in a 50.1 % reduction in radiotracer uptake in DU145 cells. Small animal PET imaging revealed 0.86 ± 0.13 and 1.6 ± 0.2 % ID/g at 30 min post injection of radioactivity in DU145 and PC3 subcutaneous tumor bearing mice respectively.

CONCLUSION

Herein, we evaluated a F-18-labeled PKM2-specific radiotracer, [18F]DASA-23, for the molecular imaging of prostate cancer with PET. [18F]DASA-23 revealed rapid and extensive uptake levels in cellular uptake studies of prostate cancer cells; however, there was only modest tumor uptake when evaluated in mouse subcutaneous tumor models.

Clinical perspectives of PSMA PET/MRI for prostate cancer

Prostate cancer imaging has become an important diagnostic modality for tumor evaluation. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) has been extensively studied, and the results are robust and promising. The advent of the PET/magnetic resonance imaging (MRI) has added morphofunctional information from the standard of reference MRI to highly accurate molecular information from PET. Different PSMA ligands have been used for this purpose including 68gallium and 18fluorine-labeled PET probes, which have particular features including spatial resolution, imaging quality and tracer biodistribution. The use of PSMA PET imaging is well established for evaluating biochemical recurrence, even at low prostate-specific antigen (PSA) levels, but has also shown interesting applications for tumor detection, primary staging, assessment of therapeutic responses and treatment planning. This review will outline the potential role of PSMA PET/MRI for the clinical assessment of PCa.

Clinical PET Imaging in Prostate Cancer

Prostate cancer is the second most common cancer in men worldwide, with a wide spectrum of biologic behavior ranging from indolent low-risk disease to highly aggressive castration-resistant prostate cancer. Conventional imaging with computed tomography, magnetic resonance imaging, and bone scintigraphy is limited for the detection of nodal disease and distant bone metastases. In addition, advances in the available therapeutic options, both localized and systemic, drive the requirement for precise diagnostic and prognostic tools to refine the individual therapeutic approach at various times in the management of patients with prostate cancer. Positron emission tomography (PET) has a rapidly evolving role in the assessment of prostate cancer, particularly in the scenario of biochemical relapse. Fluorine 18 (¹⁸F) fluorodeoxyglucose, the most widely available PET tracer, has limitations, particularly in indolent prostate cancer. In the past decade, several PET tracers with specific molecular targets have reached the clinical domain. These tracers include ¹⁸F-sodium fluoride, which is a bone-specific biomarker of osteoblastic activity; ¹⁸F-choline and carbon 11-choline, which are directed at cell membrane metabolism; gallium 68-prostate-specific membrane antigen ligands; and, more recently, an amino acid analog, ¹⁸F-fluciclovine (anti-1-amino-3-¹⁸F-fluorocyclobutane-1-carboxylic acid; also known as FACBC), which is also directed at cell membrane turnover. The mechanisms of actions of the clinically available PET tracers are reviewed, as well as their role in the imaging of prostate cancer with reference to relevant guidelines and the technical and imaging pearls and pitfalls of these tracers. ^©RSNA, 2017.

Update on advances in molecular PET in urological oncology

Integrated positron emission tomography/computed tomography (PET/CT) with 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)F-FDG) has emerged as a powerful tool for the combined metabolic and anatomic evaluation of many cancers. In urological oncology, however, the use of (18)F-FDG has been limited by a generally low tumor uptake, and physiological excretion of FDG through the urinary system. (18)F-FDG PET/CT is useful when applied to specific indications in selected patients with urological malignancy. New radiotracers and positron emission tomography/magnetic resonance imaging (PET/MRI) are expected to further improve the performance of PET in uro-oncology.

18F-fluorodeoxyglucose PET/CT for detection of disease in patients with prostate-specific antigen relapse following radical treatment of a local-stage prostate cancer

The present study aimed to retrospectively review the contribution of ¹⁸F-fluorodeoxygluose-positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) in the assessment of biochemical recurrence in patients with a diagnosis of local-stage prostate cancer (PCa) who underwent radical prostatectomy (RP) or received external beam radiation therapy (EBRT). A total of 28 patients who underwent RP or received EBRT for PCa between July 2007 and April 2013, and who underwent ¹⁸F-FDG PET/CT scanning for re-staging due to biochemical recurrence were included in the present study. The mean age of the patients was 65.07 years and the standard deviation was 7.51 years (range, 51-82 years). Of the 28 patients, 23 (82.1%) underwent RP and 5 (17.9%) received definitive EBRT. Prior to scanning, all patients were required to fast for 6 h, and ~1 h after the intravenous injection of 555 MBq ¹⁸F-FDG, whole-body PET scans were performed from the skull base to the upper thighs. Whole-body CT scans were performed in the craniocaudal direction. ¹⁸F-FDG PET images were reconstructed using CT data for attenuation correction. Histopathology examination or clinical follow-up was used to confirm any suspicious recurrent or metastatic lesions. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of ¹⁸F-FDG PET/CT were 61.6, 75.0, 61.6, 75.0 and 71.4%, respectively. ¹⁸F-FDG PET/CT can detect local and distant metastases with a high accuracy in the assessment of biochemical recurrence, thus detecting occult metastases and allowing the re-staging of PCa in the patients receiving definitive treatment. It is considered that ¹⁸F-FDG PET/CT may be useful in re-assessing the patients with PCa receiving definitive treatment.

Preclinical evaluation of the novel monoclonal antibody H6-11 for prostate cancer imaging

The biological properties of the novel monoclonal antibody (mAb) H6-11 and its potential utility for oncological imaging studies were evaluated using in vitro and in vivo assays. Immunoreactivity of H6-11 to the human prostate cancer PC-3 cell line and solid tumor xenografts was initially demonstrated using immunofluorescence staining; the specificity of H6-11 for prostate cancer was further evaluated using a commercial array of human prostate cancer and normal tissue samples (n=49) in which H6-11 detected 95% of prostate adenocarcinomas. The Kd value of 61.7±30 nM was determined using 125I-labeled H6-11. Glycosylation analysis suggested the antigenic epitope of the glycan is an O-linked β-N-acetylglucoside (O-GlcNAc) group. Imaging studies of PC-3 tumor-bearing mice were performed using both optical imaging with NIR fluorescent dye-labeled H6-11 and microPET imaging with 89Zr-labeled H6-11. These in vivo studies revealed that the labeled probes accumulated in PC-3 tumors 48-72 h postinjection, although significant retention in liver was also observed. By 120 h postinjection, the tumors were still evident, although the liver showed significant clearance. These studies suggest that the mAb H6-11 may be a useful tool to detect prostate cancer in vitro and in vivo.

Update on positron emission tomography for imaging of prostate cancer

Prostate cancer is the most common non-cutaneous malignancy among men in the Western world, and continues to be a major health problem. Imaging has recently become more important in the clinical management of prostate cancer patients, including diagnosis, staging, choice of optimal treatment strategy, treatment follow up and restaging. Positron emission tomography, a functional and molecular imaging technique, has opened a new field in clinical oncological imaging. The most common positron emission tomography radiotracer, 18F-fluorodeoxyglucose, has been limited in imaging of prostate cancer. Recently, however, other positron emission tomography tracers, such as 11C-acetate and 11C- or (18) F-choline, have shown promising results. In the present review article, we overview the potential and current use of positron emission tomography or positron emission tomography/computed tomography imaging employing the four most commonly used positron emission tomography radiotracers, 18F-fluorodeoxyglucose, 11C-acetate and 11C- or 18F-choline, for imaging evaluation of prostate cancer.

Evaluation of androgen-induced effects on the uptake of [18F]FDG, [11C]choline and [11C]acetate in an androgen-sensitive and androgen-independent prostate cancer xenograft model

Background

Androgen deprivation (AD) is generally used as a first-line palliative treatment in prostate cancer (PCa) patients with rising prostate-specific antigen (PSA) after primary therapy. To acquire an accurate detection of tumour viability following AD with positron emission tomography (PET), an androgen-independent uptake of tracers would be advantageous. Several metabolic PET tracers are employed for detecting recurrent PCa. We evaluated the effect of AD on the uptake of 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG), [¹¹C]choline and [¹¹C]acetate in vivo.

Methods

An [¹⁸F]FDG, [¹¹C]choline and [¹¹C]acetate baseline micro(μ)PET/μ computed tomography (CT) scan was subsequently performed in xenografts of androgen-sensitive (LAPC-4) and androgen-independent (22Rv1) tumours in nude mice. An untreated control group was compared to a surgical castration group, i.e. androgen-deprived group. μPET/μCT imaging with the above-mentioned tracers was repeated 5 days after the start of treatment. The percentage change of SUV_max and SUV_meanTH in the tumours was calculated.

Results

AD did not significantly affect the uptake of [¹⁸F]FDG and [¹¹C]choline in LAPC-4 tumours as compared with the uptake of both tracers in untreated tumours. In control 22Rv1 tumours, [¹¹C]choline and [¹⁸F]FDG uptake increased over time. However, compared with the uptake in control tumours, AD significantly decreased the uptake of [¹¹C]choline and tended to decrease [¹⁸F]FDG uptake. [¹¹C]acetate uptake remained unaffected by AD in both PCa xenograft models.

Conclusions

[¹⁸F]FDG and especially [¹¹C]choline PET, which is currently used for the detection of recurrent PCa, could miss or underestimate the presence of local recurrent PCa following AD therapy. [¹¹C]acetate uptake occurs independently of androgens and thus may be more favourable for detecting tumour viability during or following AD.

Imaging evaluation of prostate cancer with 18F-fluorodeoxyglucose PET/CT: utility and limitations

Prostate cancer is a major public health problem in developed countries. The remarkable biological and clinical heterogeneity of prostate cancer provides unique opportunities as well as challenges for the diagnostic imaging evaluation of this prevalent disease. The disease is characterized by a natural history that ranges from localized slowly growing hormone-dependent tumor progressing to metastatic hormone-refractory disease. PET is an ideal imaging tool for noninvasive interrogation of the underlying tumor biology. (18)F-FDG is the most common PET radiotracer used for oncological applications based upon elevated glucose metabolism in malignant tissue in comparison to normal tissue. FDG uptake in prostate cancer depends on tumor differentiation with low accumulation in well-differentiated tumors and high uptake in aggressive poorly differentiated tumors. Cumulative current evidence suggests that FDG PET may be useful in detection of disease in a small fraction of patients with biochemical recurrence, in the imaging evaluation of extent and treatment response in metastatic disease and in prediction of patient outcome.

Molecular imaging of prostate cancer: PET radiotracers

OBJECTIVE

Recent advances in the fundamental understanding of the complex biology of prostate cancer have provided an increasing number of potential targets for imaging and treatment. The imaging evaluation of prostate cancer needs to be tailored to the various phases of this remarkably heterogeneous disease.

CONCLUSION

In this article, I review the current state of affairs on a range of PET radiotracers for potential use in the imaging evaluation of men with prostate cancer.

Assessment of PET tracer uptake in hormone-independent and hormone-dependent xenograft prostate cancer mouse models

The pharmacokinetics of (18)F-fluorodeoxythymidine (FLT), (18)F-FDG, (11)C-choline, and (18)F-fluoroethylcholine (FEC) in 2 hormone-independent (PC-3, DU145) and 2 hormone-dependent (CWR22, PAC120) prostate cancer xenograft mouse models were evaluated by PET and compared by immunohistochemistry. Further investigation was performed to determine whether PET can detect early changes in tumor metabolism after androgen ablation therapy through surgical castration.

METHODS

PET was performed on 4 consecutive days. In addition, the CWR22 and PAC120 tumor models were surgically castrated after the baseline measurement and imaged again after castration. The tracer uptake was analyzed using time-activity curves, percentage injected dose per volume (%ID/cm(3)), and tumor-to-muscle ratio (T/M).

RESULTS

Regarding the hormone-independent prostate tumor models, (18)F-FLT showed the best T/M and highest %ID/cm(3) in PC-3 (2.97 ± 0.63 %ID/cm(3)) and DU145 (2.06 ± 0.75 %ID/cm(3)) tumors. (18)F-FDG seemed to be the tracer of choice for delineation of the PC-3 tumors but not for the DU145 tumors. Using (11)C-choline (PC-3: 1.33 ± 0.29 %ID/cm(3), DU145: 1.60 ± 0.27 %ID/cm(3)) and (18)F-FEC, we did not find any significant uptake in the tumors, compared with muscle tissue. Regarding the hormone-dependent prostate tumor models, the CWR22 model showed a highly significant (P < 0.01) decrease in tumor (18)F-FDG uptake from 4.11 ± 1.29 %ID/cm(3) to 2.19 ± 1.45 %ID/cm(3) after androgen ablation therapy. However, the (18)F-FLT, (11)C-choline, or (18)F-FEC tracers did not provide sufficient uptake or reliable information about therapy response in CWR22 tumors. The PAC120 model showed a significant increase in (18)F-FLT tumor uptake (P = 0.015) after androgen ablation therapy. The accumulation of (18)F-FEC (before: 2.32 ± 1.01 %ID/cm(3), after: 1.36 ± 0.39 %ID/cm(3)) was found to be the next highest after (18)F-FDG (before: 2.45 ± 0.93 %ID/cm(3), after: 2.18 ± 0.65 %ID/cm(3)) in PAC120 tumors before castration and is better suited for monitoring therapy response.

CONCLUSION

This comprehensive study in 2 hormone-dependent and 2 hormone-independent prostate tumor mouse models shows that (18)F-FLT and (18)F-FDG are the most appropriate tracers for delineation of PC-3, DU145 (except (18)F-FDG), and CWR22 tumors, but not for PAC120 tumors. (18)F-FEC and (11)C-choline, in particular, revealed insufficient T/M ratio in the prostate tumor models. The results may indicate that radiolabeled choline and choline derivatives compete with a high concentration of the precursor dimethylaminoethanol, resulting in reduced uptake in small-rodent tumor models, a hypothesis that is currently under investigation in our laboratory.

Use of DNA microarray and small animal positron emission tomography in preclinical drug evaluation of RAF265, a novel B-Raf/VEGFR-2 inhibitor

Positron emission tomography (PET) imaging has become a useful tool for assessing early biologic response to cancer therapy and may be particularly useful in the development of new cancer therapeutics. RAF265, a novel B-Raf/vascular endothelial growth factor receptor-2 inhibitor, was evaluated in the preclinical setting for its ability to inhibit the uptake of PET tracers in the A375M(B-Raf(V600E)) human melanoma cell line. RAF265 inhibited 2-deoxy-2-[(18)F]fluoro-d-glucose (FDG) accumulation in cell culture at 28 hours in a dose-dependent manner. RAF265 also inhibited FDG accumulation in tumor xenografts after 1 day of drug treatment. This decrease persisted for the remaining 2 weeks of treatment. DNA microarray analysis of treated tumor xenografts revealed significantly decreased expression of genes regulating glucose and thymidine metabolism and revealed changes in apoptotic genes, suggesting that the imaging tracers FDG, 3-deoxy-3-[(18)F]fluorothymidine, and annexin V could serve as potential imaging biomarkers for RAF265 therapy monitoring. We concluded that RAF265 is highly efficacious in this xenograft model of human melanoma and decreases glucose metabolism as measured by DNA microarray analysis, cell culture assays, and small animal FDG PET scans as early as 1 day after treatment. Our results support the use of FDG PET in clinical trials with RAF265 to assess early tumor response. DNA microarray analysis and small animal PET studies may be used as complementary technologies in drug development. DNA microarray analysis allows for analysis of drug effects on multiple pathways linked to cancer and can suggest corresponding imaging tracers for further analysis as biomarkers of tumor response.

Prostate cancer

Prostate cancer is biologically and clinically a heterogeneous disease and its imaging evaluation will need to be tailored to the specific phases of the disease in a patient-specific, risk-adapted manner. We first present a brief overview of the natural history of prostate cancer before discussing the role of various imaging tools, including opportunities and challenges, for different clinical phases of this common disease in men. We then review the preclinical and clinical evidence on the potential and emerging role of positron emission tomography with various radiotracers in the imaging evaluation of men with prostate cancer.

Prostate cancer: PET with 18F-FDG, 18F- or 11C-acetate, and 18F- or 11C-choline

Prostate cancer is biologically and clinically a heterogeneous disease that makes imaging evaluation challenging. The role of imaging in prostate cancer should include diagnosis, localization, and characterization (indolent vs. lethal) of the primary tumor, determination of extracapsular spread, guidance and evaluation of local therapy in organ-confined disease, staging of locoregional lymph nodes, detection of locally recurrent and metastatic disease in biochemical relapse, planning of radiation treatment, prediction and assessment of tumor response to salvage and systemic therapy, monitoring of active surveillance and definition of a trigger for definitive therapy, and prognostication of time to hormone refractoriness in castrate disease and overall survival. To address these tasks effectively, imaging needs to be tailored to the specific phases of the disease in a patient-specific, risk-adjusted manner. In this article, I review the preclinical and clinical evidence on the potential and emerging role of PET with the 3 most commonly studied radiotracers in prostate cancer, namely 18F-FDG, 18F- or 11C-acetate, and 18F- or 11C-choline.

Serially heterotransplanted human prostate tumours as an experimental model

* Introduction * Serially heterotransplanted human tumours in immunosuppressed mice: similarity to the tumour of origin - Cytological and histological analysis - Karyotype - Marker expression - Other PC markers - Tumour cell proliferation and frequency of mitosis - Vasculature - Stromal compartment - Heterotransplant hormone dependency - Androgen dependent - Partially androgen dependent - Androgen independent - Metastases * Conclusions Preclinical research on prostate cancer (PC) therapies uses several models to represent the human disease accurately. A common model uses patient prostate tumour biopsies to develop a cell line by serially passaging and subsequent implantation, in immunodeficient mice. An alternative model is direct implantation of patient prostate tumour biopsies into immunodeficient mice, followed by serial passage in vivo. The purpose of this review is to compile data from the more than 30 years of human PC serial heterotransplantation research. Serially heterotransplanted tumours are characterized by evaluating the histopathology of the resulting heterotransplants, including cellular differentiation, karyotype, marker expression, hormone sensitivity, cellular proliferation, metastatic potential and stromal and vascular components. These data are compared with the initial patient tumour specimen and, depending on available information, the patient's clinical outcome was compared with the heterotransplanted tumour. The heterotansplant model is a more accurate preclinical model than older generation serially passaged or genetic models to investigate current and newly developed androgen-deprivation agents, antitumour compounds, anti-angiogenic drugs and positron emission tomography radiotracers, as well as new therapeutic regimens for the treatment of PC.

Molecular imaging of prostate cancer with 18F-fluorodeoxyglucose PET

Prostate cancer poses a major public health problem, particularly in the US and Europe, where it constitutes the most common type of malignancy among men, excluding nonmelanoma skin cancers. The disease is characterized by a wide spectrum of biological and clinical phenotypes, and its evaluation by imaging remains a challenge in view of this heterogeneity. Imaging in prostate cancer can be used in the initial diagnosis of the primary tumor, to determine the occurrence and extent of any extracapsular spread, for guidance in delivery and evaluation of local therapy in organ-confined disease, in locoregional lymph node staging, to detect locally recurrent and metastatic disease in biochemical relapse, to predict and assess tumor response to systemic therapy or salvage therapy, and in disease prognostication (in terms of the length of time taken for castrate-sensitive disease to become refractory to hormones and overall patient survival). Evidence from animal-based translational and human-based clinical studies points to a potential and emerging role for PET, using F-fluorodeoxyglucose as a radiotracer, in the imaging evaluation of prostate cancer.

PET and Radiation Therapy Planning and Delivery for Prostate Cancer

PET imaging has become an integral component of the diagnosis and management of a substantial number of lymphatic and solid malignancies. One of the greatest dilemmas in prostate cancer remains the need for greater personalization of treatment recommendations based on the true extent of disease, so that patients with extraprostatic, micrometastatic disease can be identified early and managed accordingly. These sites currently remain under the level of detection with standard imaging and continue to confound clinicians. Novel PET tracers to complement anatomic data from CT and MR imaging can truly make a difference, and ongoing research holds the greatest promise.

[F-18]-fluorodeoxyglucose PET-CT of the normal prostate gland

OBJECTIVE

We determined the glucose metabolism and computed tomographic (CT) density of the normal prostate gland in relation to age and prostate size on [F-18] fluorodeoxyglucose positron emission tomography (PET)-CT.

METHODS

We determined the CT density (Hounsfield Units, HU) and glucose metabolism (standardized uptake value, SUV) of the normal prostate in 145 men (age range 22-97 years) on PET-CT scans which were performed for indications unrelated to prostate pathology. Correlations among SUV, HU, prostate size, and age were calculated using Pearson's correlation coefficients, scatter plots, and linear regression trend lines. The SUV and HU values were also compared among different primary cancer types using the Kruskal-Wallis test.

RESULTS

The population average and range of the normal prostate size were 4.3 +/- 0.5 cm (mean +/- SD) and 2.9-5.5 cm, respectively. The population average of mean and maximum CT densities was 36.0 +/- 5.1 HU (range 23-57) and 91.7 +/- 20.1 HU (range 62-211), respectively. The population average of mean and maximum SUV was 1.3 +/- 0.4 (range 0.1-2.7) and 1.6 +/- 0.4 (range 1.1-3.7), respectively. Mean SUV tended to decrease as the prostate size increased (r = -0.16, P = 0.058). Higher mean HU was correlated with higher mean SUV (r = 0.18, P = 0.033). The strongest association was observed between age and prostate size. The prostate gets larger as age increases (r = 0.32, P < 0.001). Prostate mean SUV, max SUV, mean HU, and max HU were not significantly different among different types of primary cancers.

CONCLUSIONS

Although the normal prostate size increases with age, it does not significantly affect the gland's metabolism and CT density, and therefore age-correction of these parameters may be unnecessary.

Current issues and perspectives in small rodent magnetic resonance imaging using clinical MRI scanners

Small rodents such as mice and rats are frequently used in animal experiments for several reasons. In the past, animal experiments were frequently associated with invasive methods and groups of animals had to be killed to perform longitudinal studies. Today's modern imaging techniques such as magnetic resonance imaging (MRI) allow non-invasive longitudinal monitoring of multiple parameters. Although only a few institutions have access to dedicated small animal MR scanners, most institutions carrying out animal experiments have access to clinical MR scanners. Technological advances and the increasing field strength of clinical scanners make MRI a broadly available and viable technique in preclinical in vivo research. This review provides an overview of current concepts, limitations, and recent studies dealing with small animal imaging using clinical MR scanners.