Combined magnetic resonance imaging and spectroscopic imaging approach to molecular imaging of prostate cancer

Automatic brachytherapy seed placement under MRI guidance

The paper presents a robotic method of performing low dose rate prostate brachytherapy under magnetic resonance imaging (MRI) guidance. The design and operation of a fully automated MR compatible seed injector is presented. This is used with the MrBot robot for transperineal percutaneous prostate access. A new image-registration marker and algorithms are also presented. The system is integrated and tested with a 3T MRI scanner. Tests compare three different registration methods, assess the precision of performing automated seed deployment, and use the seeds to assess the accuracy of needle targeting under image guidance. Under the ideal conditions of the in vitro experiments, results show outstanding image-guided needle and seed placement accuracy.

Prostate cancer: sextant localization with MR imaging, MR spectroscopy, and 11C-choline PET/CT

PURPOSE

To retrospectively compare sensitivity and specificity of magnetic resonance (MR) imaging, three-dimensional (3D) MR spectroscopy, combined MR imaging and 3D MR spectroscopy, and carbon 11 (11C)-choline positron emission tomography (PET)/computed tomography (CT) for intraprostatic tumor sextant localization, with histologic findings as reference standard.

MATERIALS AND METHODS

The local ethics committee on human research provided approval and a waiver of informed consent for the retrospective study. MR imaging, 3D MR spectroscopy, and 11C-choline PET/CT results were retrospectively reviewed in 26 men with biopsy-proved prostate cancer (mean age, 64 years; range, 51-75 years) who underwent radical prostatectomy. Cancer was identified as areas of nodular low signal intensity on T2-weighted MR images. At 3D MR spectroscopy, choline-plus-creatine-to-citrate and choline-to-creatine ratios were used to distinguish healthy from malignant voxels. At PET/CT, focal uptake was visually assessed, and maximum standardized uptake values (SUVs) were recorded. Agreement between 3D MR spectroscopic and PET/CT results was calculated, and ability of maximum SUV to help localize cancer was assessed with receiver operating characteristic analysis. Significant differences between positive and negative sextants with respect to mean maximum SUV were calculated with a paired t test.

RESULTS

Sensitivity, specificity, and accuracy were, respectively, 55%, 86%, and 67% at PET/CT; 54%, 75%, and 61% at MR imaging; and 81%, 67%, and 76% at 3D MR spectroscopy. The highest sensitivity was obtained when either 3D MR spectroscopic or MR imaging results were positive (88%) at the expense of specificity (53%), while the highest specificity was obtained when results with both techniques were positive (90%) at the expense of sensitivity (48%). Concordance between 3D MR spectroscopic and PET/CT findings was slight (kappa=0.139).

CONCLUSION

In localizing cancer within the prostate, comparable specificity was obtained with either 3D MR spectroscopy and MR imaging or PET/CT; however, PET/CT had lower sensitivity relative to 3D MR spectroscopy alone or combined with MR imaging.

3D MR spectroscopic imaging in the evaluation of prostate cancer

The management of prostate cancer is a complex issue with a varying range of treatment options available. Magnetic resonance (MR) imaging of the prostate has been available for sometime but has the limitation of only anatomical evaluation. Three-dimensional MR spectroscopy is emerging as a new and sensitive tool in the metabolic evaluation of prostate cancer. This article reviews the principle, techniques, and methods of evaluation of spectroscopy and also discusses the applications of spectroscopy in the current management of prostate cancer.

Computer-aided diagnosis of prostate cancer with emphasis on ultrasound-based approaches: a review

This paper reviews the state of the art in computer-aided diagnosis of prostate cancer and focuses, in particular, on ultrasound-based techniques for detection of cancer in prostate tissue. The current standard procedure for diagnosis of prostate cancer, i.e., ultrasound-guided biopsy followed by histopathological analysis of tissue samples, is invasive and produces a high rate of false negatives resulting in the need for repeated trials. It is against these backdrops that the search for new methods to diagnose prostate cancer continues. Image-based approaches (such as MRI, ultrasound and elastography) represent a major research trend for diagnosis of prostate cancer. Due to the integration of ultrasound imaging in the current clinical procedure for detection of prostate cancer, we specifically provide a more detailed review of methodologies that use ultrasound RF-spectrum parameters, B-scan texture features and Doppler measures for prostate tissue characterization. We present current and future directions of research aimed at computer-aided detection of prostate cancer and conclude that ultrasound is likely to play an important role in the field.

Prostate Cancer: Body-Array versus Endorectal Coil MR Imaging at 3 T—Comparison of Image Quality, Localization, and Staging Performance

PURPOSE

To prospectively compare image quality and accuracy of prostate cancer localization and staging with body-array coil (BAC) versus endorectal coil (ERC) T2-weighted magnetic resonance (MR) imaging at 3 T, with histopathologic findings as the reference standard.

MATERIALS AND METHODS

After institutional review board approval and written informed consent, 46 men underwent 3-T T2-weighted MR imaging with a BAC (voxel size, 0.43 x 0.43 x 4.00 mm) and an ERC (voxel size, 0.26 x 0.26 x 2.50 mm) before radical prostatectomy. Four radiologists independently evaluated data sets obtained with the BAC and ERC separately. Ten image quality characteristics related to prostate cancer localization and staging were assigned scores. Prostate cancer presence was recorded with a five-point probability scale in each of 14 segments that included the whole prostate. Disease stage was classified as organ-confined or locally advanced with a five-point probability scale. Whole-mount-section histopathologic examination was the reference standard. Areas under the receiver operating characteristic curve (AUCs) and diagnostic performance parameters were determined. A difference with a P value of less than .05 was considered significant.

RESULTS

Forty-six patients (mean age, 61 years) were included for analysis. Significantly more motion artifacts were present with ERC imaging (P<.001). All other image quality characteristics improved significantly (P<.001) with ERC imaging. With ERC imaging, the AUC for localization of prostate cancer was significantly increased from 0.62 to 0.68 (P<.001). ERC imaging significantly increased the AUCs for staging, and sensitivity for detection of locally advanced disease by experienced readers was increased from 7% (one of 15) to a range of 73% (11 of 15) to 80% (12 of 15) (P<.05), whereas a high specificity of 97% (30 of 31) to 100% (31 of 31) was maintained. Extracapsular extension as small as 0.5 mm at histopathologic examination could be accurately detected only with ERC imaging.

CONCLUSION

Image quality and localization improved significantly with ERC imaging compared with BAC imaging. For experienced radiologists, the staging performance was significantly better with ERC imaging.

Strategies for improved temporal and spectral resolution in in vivo oximetric imaging using time-domain EPR

A radiofrequency (RF) time-domain electron paramagnetic resonance (EPR) instrument operating at 300, 600, and 750 MHz was used to image tumor hypoxia with high spatial and temporal resolution. A high-speed signal-averaging Peripheral Component Interconnect (PCI) board with flexibility in the input signal level and the number of digitized samples per free induction decay (FID) was incorporated into the receive arm of the spectrometer. This enabled effective and fast averaging of FIDs. Modification of the phase-encoding protocol, and replacement of the General Purpose Interface Bus (GPIB)-based handshake with a PCI-based D/A board for direct control of the gradient amplifier decreased the gradient settling and communication overhead times by nearly two orders of magnitude. Cyclically-ordered phase sequence (CYCLOPS) phase cycling was implemented to correct for pulse imperfections and cancel out unwanted constant signals. These upgrades considerably enhanced the performance of the imager in terms of image collection time, sensitivity, and temporal resolution. We demonstrated this by collecting a large number of 2D images successively and rapidly. The results show that it is feasible to achieve accurate, 2D pO(2) maps of tumor hypoxia with 1-mm(2) resolution and minimal artifacts using a set of multigradient images within an acceptable measuring time of about 3 s, and 3D maps can be obtained in less than 1 min.

Prostate cancer detection: magnetic resonance (MR) spectroscopic imaging

Magnetic resonance spectroscopic imaging (MRSI) represents a noninvasive technique to extend the diagnostic evaluation of prostatic cancer, beyond the morphologic information provided by MR imaging throughout the detection of cellular metabolites (choline and citrate). MRSI combined with the anatomical information provided by MRI can improve the assessment cancer location and extent within the prostate, extracapsular spread and cancer aggressiveness; both before and after treatment. We review the performance of MRI with MRSI and the role in the detection, localization, staging and management of the patient pre- and posttherapy for prostate cancer.

Methods for acquisition and assignment of multidimensional high-resolution magic angle spinning NMR of whole cell bacteria

High-resolution magic-angle spinning (HR-MAS) NMR was developed in late 1990s, and it has evolved quickly for the study of a variety of biological matrixes. Recently, it has been used as an effective means to study the cell wall structures of intact bacteria. (1)H-(13)C heteronuclear single quantum coherence (HSQC) HR-MAS NMR can provide rapid analysis of the cell wall structure in live bacterial cells, thus allowing observation of drug effects, gene mutation, species differentiation, and environmental effects. However, this rapid analysis is dependent on having an established framework of HR-MAS NMR experiments and a detailed assignment of the whole-cell NMR spectra. This study examines parameters and describes strategies for the effective application of 2D and 3D HR-MAS NMR techniques to assign and study bacterial cell wall structures using Mycobacterium smegmatis as a model organism. Important parameters for successful whole-cell HR-MAS NMR studies, including pulse sequences, rotor synchronization, acquisition times, labeling strategies, temperature, number of cells, and cell viability, are described. A four-prong approach is presented for assignment of the complex whole-cell spectra, including the use of 3D HCCH-TOCSY and HCCH-COSY HR-MAS NMR.

Prostate cancer screening: the clinical value of diffusion-weighted imaging and dynamic MR imaging in combination with T2-weighted imaging

PURPOSE

To evaluate the clinical value of diffusion-weighted imaging (DWI) and dynamic MRI in combination with T2-weighted imaging (T2W) for the detection of prostate cancer.

MATERIALS AND METHODS

A total of 83 patients with elevated serum prostate specific antigen (PSA) levels (>4.0 ng/mL) were evaluated by T2W, DWI, and dynamic MRI at 1.5 T prior to needle biopsy. The data from the results of the T2W alone (protocol A), combination of T2W and DWI (protocol B), and the combination of T2W+DWI and dynamic MRI (protocol C) were entered into a receiver operating characteristic (ROC) curve analysis, under results of systemic biopsy as the standard of reference.

RESULTS

Prostate cancer was pathologically detected in 44 of the 83 patients. The sensitivity, specificity, accuracy, and the area under the ROC curve (Az) for the detection of prostate cancer were as follows: 73%, 54%, 64%, and 0.711, respectively, in protocol A; 84%, 85%, 84%, and 0.905, respectively, in protocol B; and 95%, 74%, 86%, and 0.966, respectively, in protocol C. The sensitivity, specificity, and accuracy were significantly different between the three protocols (P < 0.01).

CONCLUSION

In patients with elevated serum PSA levels, the combination of T2W, DWI, and dynamic MRI may be a valuable tool for detecting prostate cancer and avoiding an unnecessary biopsy without missing prostate cancer.

Choline metabolism in cancer: implications for diagnosis and therapy

Magnetic resonance studies from the last 10 years have conclusively demonstrated that choline metabolism is altered in a wide variety of cancers. In cancer, the choline metabolite profile is characterized by an elevation of phosphocholine and total choline-containing compounds. This elevation is increasingly being used as an endogenous biomarker of cancer. Importantly, the enzymes and pathways resulting in these distinct alterations in phosphocholine and total choline may provide novel molecular targets for specific, targeted anticancer therapies. In this article, we have summarized some of the magnetic resonance spectroscopy and positron emission tomography techniques that are currently available, or will be in the near future, for choline metabolism-based diagnosis, staging and therapy assessment in cancer patients. This review also outlines currently known molecular alterations that cause the aberrant choline metabolite profile in cancers and concludes with a summary of recent research findings that may, in the future, lead to novel anticancer therapies targeting choline metabolism.

Diagnosis of Prostate Cancer in Patients with an Elevated Prostate-Specific Antigen Level: Role of Endorectal MRI and MR Spectroscopic Imaging

OBJECTIVE

The objective of our study was to determine the accuracy of endorectal MRI and MR spectroscopic imaging (MRSI) in the diagnosis of prostate cancer in patients with an elevated serum prostate-specific antigen (PSA) level.

MATERIALS AND METHODS

We retrospectively identified 40 patients with an elevated serum PSA level and without a histologic diagnosis of prostate cancer who underwent endorectal MRI and MRSI at our institution. On the basis of MRI findings alone and then combined MRI and MRSI findings, a single experienced observer rated the presence or absence of prostate cancer in each side of the prostate on a 5-point scale (1 = definitely absent, 5 = definitely present). Areas under the receiver operating characteristic (ROC) curve were calculated using the hemiprostate as the unit of analysis. The presence or absence of cancer on subsequent endorectal sonographically guided sextant biopsy was used as the standard of reference.

RESULTS

Biopsy revealed no cancer in 24 patients, bilateral cancer in 11, and unilateral cancer in five. The areas under the ROC curve for the diagnosis of prostate cancer by hemigland was 0.70 for MRI alone and 0.63 for combined MRI and MRSI (no significant difference, p = 0.32).

CONCLUSION

Endorectal MRI and MRSI are reasonably accurate for the diagnosis of prostate cancer in patients with an elevated serum PSA level, but the remaining limitations suggest that MRI and MRSI should be used as a supplement rather than a replacement for biopsy using the current technology and diagnostic criteria.

Transrectal ultrasound-guided biopsy of prostate voxels identified as suspicious of malignancy on three-dimensional (1)H MR spectroscopic imaging in patients with abnormal digital rectal examination or raised prostate specific antigen level of 4-10 ng/ml

Results of the evaluation of transrectal ultrasound (TRUS) guided needle biopsy of voxels identified as suspicious of malignancy on magnetic resonance spectroscopic imaging (MRSI) in a large cohort of men (n = 83) with abnormal digital rectal examination (DRE) [prostate specific antigen (PSA) 0-4 ng/ml] or PSA less than 10 ng/ml, are reported. Three-dimensional (1)H MRSI was carried out at 1.5 T using a pelvic-phased array coil in combination with an endorectal surface coil. Voxels were classified as suspicious of malignancy based on Cit/(Cho + Cr) metabolite ratio. TRUS-guided biopsy of suspicious voxels was performed using the z- and x-coordinates obtained from MR images and two to three cores were taken from the suspected site. A systematic sextant biopsy was also carried out. MRSI showed voxels suspicious of malignancy in 44 patients while biopsy revealed cancer in 11 patients (25%). Patients who were negative for malignancy on MRSI were also negative on biopsy. An overall sensitivity of 100%, specificity of 54%, negative predictive value of 100% and accuracy of 60% were obtained. The site of biopsy was confirmed (n = 20) as a hypo-intense area on repeat MRI while repeat MRSI revealed high choline and low citrate. The overall success rate of MRI-directed TRUS-guided biopsy of 25% was higher compared with a 9% success rate achieved without MR guidance in another group of 120 patients. Our results indicate that TRUS-guided biopsy of suspicious area identified as malignant from MRSI can be performed using the coordinates of the voxel derived from MR images. This increases the detection rate of prostate cancer in men with PSA level <10 ng/ml or abnormal DRE and also demonstrates the potential of MR in routine clinical practice.

Prostate spectroscopy at 3 Tesla using two-dimensional S-PRESS

Two-dimensional (2D) strong-coupling point-resolved spectroscopy (S-PRESS) is introduced as a novel approach to (1)H MR spectroscopy (MRS) in the prostate. The technique provides full spectral information and allows for an accurate characterization of the citrate (Cit) signal. The method is based on acquiring a series of PRESS spectra with constant total echo time (TE). The indirect dimension is encoded by varying the relative lengths of the first and second TEs (TE(1) + TE(2) = TE). In the resulting 2D spectra, only the signal of strongly coupled spin systems is spread into the second dimension, which leads to more clearly arranged spectra. Furthermore, the spectral parameters of Cit (coupling constant J and chemical shift difference delta of the AB spin system) can be determined with high accuracy in vivo. The sequence is analytically optimized for maximal "strong coupling peaks" of Cit at 3T. 2D S-PRESS spectra are compared with JPRESS spectra in vitro as well as in vivo.

Robotic prostate surgery

The increasing popularity of robot-assisted radical prostatectomy has put the field of robotics in the spotlight. However, the relationship between medical robotics and the field of urology is older than most urologists know and it will most likely have a bright future beyond any contemporary application. The objective of this review is to provide an insight into the fundamentals of medical robotics and to highlight the history, the present and the future of urological robotic systems with an emphasis on robotic prostate interventions.

Irradiation adaptation to the tumor activity with the help of intensity-modulated radiation therapy for head and neck cancers

The aim of this study was to set up the appropriate geometry to perform a high-precision irradiation, based on tumor activity (TA). The elaboration of a new treatment protocol based on TA required a specific geometry in order to use this type of irradiation. Using a treatment planning system TPS and two head and neck phantoms specially created, we have performed TPS characterization according to different treatment plans. Two models were created and used: a simplistic and an anatomical model. Our results showed that high-precision radiotherapy in limited zones is possible with intensity modulated radiation therapy (IMRT) when several conditions such as location, number of Organs at risk (OAR's), distance between planning target volume (PTV) and OAR, presence, volume and location of the TA, number of fields are met. In order to use this irradiation method adapted to the TA, a precise geometry will be necessary. However such high total and fractionated doses should be carefully evaluated before being prescribed clinically.

Radiation Oncology Physicists Will Need to Better Understand Medical Imaging

Imaging is affecting radiation oncology at a dramatically advancing pace and scale and is likely to create a transformation to individualized, biologically conformal radiation therapy. Deploying and improving imaging technologies and ensuring their correct uses in treatment planning and delivery are the responsibilities of radiation oncology physicists. The potential magnitude of errors arising from the incorrect use of imaging may be far greater than that resulting from typical errors in dose calibration. A major effort is required for radiation oncology physicists to raise the quality assurance of image guidance to a level comparable with that achieved in the maintenance of dosimetric performance. Most radiation oncology physicists lack adequate knowledge to assume this emerging responsibility. Their knowledge of imaging must be enhanced, in most cases through on-the-job training and self-learning. Effective learning strategies include routine interactions with diagnostic radiology and nuclear medicine physicists and physicians and the use of educational opportunities provided by professional organizations and vendors.

"MRI Stealth" robot for prostate interventions

The paper reports an important achievement in MRI instrumentation, a pneumatic, fully actuated robot located within the scanner alongside the patient and operating under remote control based on the images. Previous MRI robots commonly used piezoelectric actuation limiting their compatibility. Pneumatics is an ideal choice for MRI compatibility because it is decoupled from electromagnetism, but pneumatic actuators were hardly controllable. This achievement was possible due to a recent technology breakthrough, the invention of a new type of pneumatic motor, PneuStep 1, designed for the robot reported here with uncompromised MRI compatibility, high-precision, and medical safety. MrBot is one of the "MRI stealth" robots today (the second is described in this issue by Zangos et al.). Both of these systems are also multi-imager compatible, being able to operate with the imager of choice or cross-imaging modalities. For MRI compatibility the robot is exclusively constructed of nonmagnetic and dielectric materials such as plastics, ceramics, crystals, rubbers and is electricity free. Light-based encoding is used for feedback, so that all electric components are distally located outside the imager's room. MRI robots are modern, digital medical instruments in line with advanced imaging equipment and methods. These allow for accessing patients within closed bore scanners and performing interventions under direct (in scanner) imaging feedback. MRI robots could allow e.g. to biopsy small lesions imaged with cutting edge cancer imaging methods, or precisely deploy localized therapy at cancer foci. Our robot is the first to show the feasibility of fully automated in-scanner interventions. It is customized for the prostate and operates transperineally for needle interventions. It can accommodate various needle drivers for different percutaneous procedures such as biopsy, thermal ablations, or brachytherapy. The first needle driver is customized for fully automated low-dose radiation seed brachytherapy. This paper gives an introduction to the challenges of MRI robot compatibility and presents the solutions adopted in making the MrBot. Its multi-imager compatibility and other preclinical tests are included. The robot shows the technical feasibility of MRI-guided prostate interventions, yet its clinical utility is still to be determined.

A turn-on fluorescent indicator for citrate with micromolar sensitivity

A turn-on fluorescent indicator for citric acid (citrate) has been developed, displaying high emission enhancement (+1500%) and low interference by other carboxylates. The sensor is based on the non-emissive copper(II) complex of a fluorescent amino amide, which, upon addition of citrate decomplexates to yield the emissive ligand. The detection limit estimated for this new chemosensing system is about 0.5 microM. This novel approach to the analysis of citrate constitutes an alternative ca. 10(2)-10(3) times more sensitive than the standard method based on the enzyme citrate lyase.

High-speed 3T MR spectroscopic imaging of prostate with flyback echo-planar encoding

Prostate MR spectroscopic imaging (MRSI) at 3T may provide two-fold higher spatial resolution over 1.5T, but this can result in longer acquisition times to cover the entire gland using conventional phase-encoding. In this study, flyback echo-planar readout trajectories were incorporated into a Malcolm Levitt's composite-pulse decoupling sequence (MLEV)-point-resolved spectroscopy sequence (PRESS) to accelerate the acquisition of large array (16 x 16 x 8), high spatial (0.154 cm(3)) resolution MRSI data by eight-fold to just 8.5 minutes. Artifact free, high-quality MRSI data was obtained in nine prostate cancer patients. Easy data reconstruction and the robustness of the flyback echo-planar encoding make this technique particularly suitable for the clinical setting. The short acquisition time provided by this method reduces the 3T prostate MRI/MRSI exam time, allows longer repetition times, and/or allows the acquisition of additional MR acquisitions within the same exam.

High-grade prostatic intraepithelial neoplasia in patients with prostate cancer: MR and MR spectroscopic imaging features--initial experience

PURPOSE

To retrospectively determine the magnetic resonance (MR) and MR spectroscopic imaging features of high-grade prostatic intraepithelial neoplasia (HGPIN) in patients with prostate cancer.

MATERIALS AND METHODS

Approval of the committee on human research was obtained, with a waiver of consent for this HIPAA-compliant study. Endorectal MR imaging and MR spectroscopic imaging were performed in 48 men (mean age, 59 years; range, 47-75 years) prior to radical prostatectomy for prostate cancer. T2-weighted signal intensity and metabolic ratios of peripheral zone HGPIN foci of 6 mm or greater in diameter were recorded by two readers with knowledge of step-section histopathologic findings using areas of confirmed normal and cancerous peripheral zone tissue for comparison. A random effects statistical model was used to compare metabolic ratios from normal, HGPIN, and cancer voxels.

RESULTS

A total of 123 peripheral zone HGPIN foci with a mean diameter of 3 mm (range, 1-28 mm) were identified in 37 (77%) patients, but only 20 foci in 14 patients had a diameter of 6 mm or greater. Six foci were excluded, yielding 14 large HGPIN lesions from 11 patients in the final statistical analysis. The larger HGPIN foci were not associated with any focal reduction in T2-weighted signal intensity but demonstrated metabolic findings intermediate between normal and cancerous tissue; the mean ratios of choline (Cho) to creatine (Cr) for normal, HGPIN, and cancer were 0.92, 1.75, and 1.99, respectively, (P < .01), and the corresponding ratios of Cho plus Cr to citrate were 0.34, 0.50, and 0.78 (P < .01).

CONCLUSION

HGPIN is metabolically intermediate between normal peripheral zone tissue and prostate cancer at MR spectroscopic imaging but does not manifest any MR imaging abnormality and is rarely of sufficient size to cause substantial error in evaluation of peripheral zone tumor extent in patients with prostate cancer.

Functional imaging in clinical oncology: magnetic resonance imaging- and computerised tomography-based techniques

Over recent years, advances in cellular biology, molecular biology and genetics have led to a leap forward in our understanding of the biological basis of cancer. Some of these developments have revealed processes and targets that can be visualised and measured by new functional imaging techniques. The resulting images have the potential to improve cancer staging, prognosis and risk assessment, guide radiotherapy planning, direct treatment schedules, improve response assessment and provide new end points for clinical trials. In this review, we have outlined the magnetic resonance imaging- and computerised tomography-based functional techniques and provide evidence for their use.

Magnetic resonance imaging compatible robotic system for fully automated brachytherapy seed placement

OBJECTIVES

To introduce the development of the first magnetic resonance imaging (MRI)-compatible robotic system capable of automated brachytherapy seed placement.

METHODS

An MRI-compatible robotic system was conceptualized and manufactured. The entire robot was built of nonmagnetic and dielectric materials. The key technology of the system is a unique pneumatic motor that was specifically developed for this application. Various preclinical experiments were performed to test the robot for precision and imager compatibility.

RESULTS

The robot was fully operational within all closed-bore MRI scanners. Compatibility tests in scanners of up to 7 Tesla field intensity showed no interference of the robot with the imager. Precision tests in tissue mockups yielded a mean seed placement error of 0.72 +/- 0.36 mm.

CONCLUSIONS

The robotic system is fully MRI compatible. The new technology allows for automated and highly accurate operation within MRI scanners and does not deteriorate the MRI quality. We believe that this robot may become a useful instrument for image-guided prostate interventions.

Clinical role of proton magnetic resonance spectroscopy in oncology: brain, breast, and prostate cancer

Standardised proton magnetic resonance spectroscopic imaging (MRSI) was initially developed for routine in-situ clinical assessment of human brain tumours, and its use was later extended for examination of prostate and breast cancers. MRSI coupled with both routine and functional MRI techniques provides more detailed information about a tumour's location and extent of its infiltration than any other modality alone. Information obtained by adding MRSI data to anatomical and functional MRI findings aid in clinical management decisions (such as watchful waiting vs immediate intervention). In this Review, we discuss the current status of proton MRSI, with emphasis on its clinical use to map the location and extent of tumour processes for spectroscopic image-guided biopsy procedures and to monitor treatment paradigms for brain, prostate, and breast cancer.

Applications of magnetic resonance spectroscopy in radiotherapy treatment planning

Following advances in conformal radiotherapy, a key problem now facing radiation oncologists is target definition. While MRI and CT provide images of excellent spatial resolution, they do not always provide sufficient contrast to identify tumour extent or to identify regions of high cellular activity that might be targeted with boost doses. Magnetic resonance spectroscopy (MRS) is an alternative approach that holds great promise for aiding target definition for radiotherapy treatment planning, and for evaluation of response and recurrence. MRS is able to detect signals from low molecular weight metabolites such as choline and creatine that are present at concentrations of a few mM in tissue. Spectra may be acquired from single voxels, or from a 2D or 3D array of voxels using spectroscopic imaging. The current state of the art achieves a spatial resolution of 6-10 mm in a scan time of about 10-15 min. Co-registered MR images are acquired in the same examination. The method is currently under evaluation, in particular in brain (where MRS has been shown to differentiate between many tumour types and grades) and in prostate (where cancer may be distinguished from normal tissue and benign prostatic hypertrophy). The contrast achieved with MRS, based on tissue biochemistry, therefore provides a promising alternative for identifying tumour extent and regions of high metabolic activity. It is anticipated that MRS will become an essential tool for treatment planning where other modalities lack the necessary contrast.

Assessing responses to cancer therapy using molecular imaging

Tumor responses to therapy in the clinic are still evaluated primarily from non-invasive imaging measurements of reductions in tumor size. This approach, however, lacks sensitivity and can only give a delayed indication of a positive response to treatment. Major advances in our understanding of the molecular mechanisms responsible for cancer, combined with new targeted clinical imaging technologies designed to detect the molecular correlates of disease progression and response to treatment, are set to revolutionize our approach to the detection and treatment of the disease. We describe here the imaging technologies available to image tumor cell proliferation and migration, metabolism, receptor and gene expression, apoptosis and tumor angiogenesis and vascular function, and show how measurements of these parameters can be used to give early indications of positive responses to treatment or to detect drug resistance and/or disease recurrence. Special emphasis has been placed on those applications that are already used in the clinic and those that are likely to translate into clinical application in the near future or whose use in preclinical studies is likely to facilitate translation of new treatments into the clinic.

Probing the Intracellular Redox Status of Tumors with Magnetic Resonance Imaging and Redox-Sensitive Contrast Agents

Nitroxide radicals are paramagnetic contrast agents, used in magnetic resonance imaging (MRI), that also exert antioxidant effects. Participating in cellular redox reactions, they lose their ability to provide contrast as a function of time after administration. In this study, the rate of contrast loss was correlated to the reducing power of the tissue or the "redox status." The preferential reduction of nitroxides in tumors compared with normal tissue was observed by MRI. The influence of the structure of the nitroxide on the reduction rate was investigated by MRI using two cell-permeable nitroxides, 4-hydroxy-2,2,6,6,-tetramethyl-1-piperidynyloxyl (Tempol) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (3CP), and one cell-impermeable nitroxide, 3-carboxy-2,2,5,5,5-tetramethylpyrrolidine-1-oxyl (3CxP). Pharmacokinetic images of these nitroxides in normal tissue, tumor, kidney, and artery regions in mice were simultaneously obtained using MRI. The decay of Tempol and 3CP in tumor tissue was significantly faster than in normal tissue. No significant change in the total nitroxide (oxidized + reduced forms) was noted from tissue extracts, suggesting that the loss in contrast as a function of time is a result of intracellular bioreduction. However, in the case of 3CxP (membrane impermeable), there was no difference in the reduction rates between normal and tumor tissue. The time course of T(1) enhancement by 3CxP and the total amount of 3CxP (oxidized + reduced) in the femoral region showed similar pharmacokinetics. These results show that the differential bioreduction of cell-permeable nitroxides in tumor and normal tissue is supported by intracellular processes and the reduction rates are a means by which the intracellular redox status can be assessed noninvasively.

Combined MRI and MR Spectroscopy of the Prostate Before Radical Prostatectomy

OBJECTIVE

The purpose of this study was to evaluate a routine protocol for combined MR and spectroscopic imaging of the prostate for staging accuracy.

SUBJECTS AND METHODS

Fifty patients with biopsy-proven prostate carcinoma were examined with our sequence protocol, which consisted of T2-weighted fast spin-echo sequences and a pelvic T1-weighted spin-echo sequence. For spectroscopy, we used a 3D chemical shift imaging (CSI) spin-echo sequence. Image interpretation was performed by two radiologists. The total number of tumor voxels and tumor voxels per slice were counted to estimate the tumor volume in every patient. The potential of MR spectroscopy to differentiate between T2 and T3 tumors, based on the estimated tumor volumes, was compared with the staging performance of MRI.

RESULTS

The MR measurement time was 19.01 minutes, and the total procedure time averaged 35 minutes. Seventy-six percent of the spectroscopic examinations were successful. Statistically significant differences in the number of tumor voxels per slice and tumor volumes were found between T2 and T3 tumors. The descriptive parameters of MRI and MR spectroscopy did not differ significantly; sensitivity and specificity were 75% and 87%, respectively, for MRI and 88% and 70%, respectively, for MR spectroscopy. The combination of both methods resulted in only a slight improvement in staging performance and was not statistically significant.

CONCLUSION

Combined MRI and MR spectroscopy of the prostate has no diagnostic advantage in staging performance over MRI alone. The mean tumor volumes, estimated by MR spectroscopy, differ statistically significantly between T2 and T3 tumors.

How good is MRI at detecting and characterising cancer within the prostate?

OBJECTIVES

As well as detecting prostate cancer, it is becoming increasingly important to estimate its location, size and grade. We aim to summarise current data on the efficacy of magnetic resonance imaging (MRI) in this setting.

METHODS

Literature review of original research correlating MRI and histologic appearances.

RESULTS

Estimates of the sensitivity of MRI for the detection of cancer vary widely depending on method of analysis used and the definition of significant disease. Recent estimates using T2-weighted sequences and endorectal coils vary from 60% to 96%. Several groups have convincingly shown that dynamic contrast enhancement and spectroscopy each improve detection and that the sensitivity of MRI is comparable to and may exceed that of transrectal biopsy. Specificity is not yet good enough to consider the use of MRI in screening. High-grade and large tumours are detected significantly more often with both T2 sequences and spectroscopy. Estimation of size is improved by dynamic contrast and spectroscopy, but errors of >25% are common.

CONCLUSIONS

The sensitivity of MRI has improved to the point that it has potential in several new areas: targeting of biopsies, monitoring of disease burden both during active surveillance and after focal therapy, and exclusion of cancer in patients with a raised prostate-specific antigen level.

Magnetic resonance spectroscopy in patients with locally confined prostate cancer: association of prostatic citrate and metabolic atrophy with time on hormone deprivation therapy, PSA level, and biopsy Gleason score

This study was undertaken to determine respective associations between prostatic citrate or metabolic atrophy (no detectable citrate, choline, and creatine) at magnetic resonance spectroscopy (MRS) and time on hormone-deprivation therapy, serum PSA, and biopsy Gleason score. Clinical data, histopathology reports and PSA levels of 36 patients on hormone-deprivation therapy (age, 64+/-9 years, pre-therapeutic biopsy Gleason sum, median 6, range 3-8, antiandrogens only, n=3, LHRH-analogues only, n=4, combined hormone-deprivation therapy, n=29, duration, 27+/-19 weeks) for locally confined prostate cancer (PCA) were retrospectively correlated with findings in the peripheral zone of the prostate at 3D-MRS (endorectal coil, PRESS, TR 1,000 ms, TE 130 ms). The results show that citrate was usually detected after 13 weeks or less of hormone-deprivation therapy (10/12 vs. 6/24 patients, chi-square-test, p=0.002). All patients with PSA levels exceeding 0.20 ng/ml had detectable metabolites (citrate, n=12, choline without citrate, n=6), while 9/18 patients with PSA 0.20 ng/ml or less showed metabolic atrophy (Fisher-exact-test, p=0.001). There were no significant associations between citrate, metabolic atrophy, pre-therapeutic PSA, and biopsy Gleason sum, respectively. It has been concluded that hormone-deprivation therapy for locally confined PCA has not reached its full deprivation potential after 13 weeks. MRS detects prostate metabolism in patients with PSA exceeding 0.20 ng/ml after hormone-deprivation therapy.

In vivo magnetic resonance volumetric and spectroscopic analysis of mouse prostate cancer models

BACKGROUND

Mouse prostate cancer modeling presents unique obstacles to the study of spontaneous tumor initiation and progression due to the anatomical location of the tissue.

RESULTS

High resolution (130 microm(x) x 130 microm(y) x 300 microm(z)), three-dimensional MRI allowed for the visualization, segmentation, and volumetric measurement of the prostate from normal and genetically engineered animals, in vivo. Additionally, MRS performed on the prostate epithelia of probasin-ErbB-2Delta x Pten(+/-) mice identified changes in the relative concentrations of the metabolites choline and citrate, which was not observed in TRAMP mice.

METHODS

T1-weighted MRI was performed on normal, TRAMP, probasin-ErbB-2/Her2/Neu (probasin-ErbB-2Delta), and probasin-ErbB-2Delta in the context of decreased Pten activity (probasin-ErbB-2Delta x Pten(+/-)) mice. Volume-localized single-voxel proton magnetic resonance spectroscopy (SVS (1)H MRS) was also performed.

CONCLUSIONS

The data presented supports the use of combined MRI and MRS for the measurement of biochemical and morphometric alterations in mouse models of prostate cancer.

The clinical relevance of the metabolism of prostate cancer; zinc and tumor suppression: connecting the dots

Background

The genetic and molecular mechanisms responsible for and associated specifically with the development and progression of malignant prostate cells are largely unidentified. In addition, despite its implication in virtually all malignant cells, the role of altered cellular metabolism as an essential factor in prostate malignancy has been largely ignored. Moreover, the intermediary metabolism of normal prostate as well as malignant prostate cells is among the least studied and most poorly understood of all mammalian cells. Some important factors, especially the role of zinc, have been identified and implicated in the development and progression of prostrate malignancy. In this review, we provide a current and updated integrated assessment of the relationships of intermediary metabolism in normal prostate and in prostate cancer. The experimental and clinical evidence that leads to the formulation of concepts of normal and malignant prostate metabolism is presented. The evidence for a concept of zinc as a tumor suppressor agent and Zip1 zinc transporter as a tumor-suppressor gene is described.

Results

The specialized function of the normal prostate glandular epithelium to produce and secrete enormously high levels of citrate involves and requires unique intermediary metabolism activities that are not generally associated with other normal mammalian cells. The accumulation of zinc by these cells is an essential factor in this unique metabolic relationship. In malignancy, the normal zinc-accumulating citrate-producing epithelial cells are metabolically transformed to citrate-oxidizing cells that lose the ability to accumulate zinc. A genetic alteration in the expression of ZIP1 zinc transporter is associated with this metabolic transformation. These genetic/metabolic relationships have important consequences on citrate-related metabolism, bioenergetics, cell proliferation and invasive capabilities of the malignant cells, which result in tumor-suppression characteristics.

Conclusion

The genetic/metabolic relationships in normal prostate glandular epithelium are driven by the unique function to accumulate and secrete citrate. The genetic/metabolic transformation of the prostate malignant cells is driven by the metabolic/bioenergetic, growth/proliferative, and invasive/migration requirements of the malignant process. Zinc is critical to these relationships. An understanding of these genetic/metabolic relationships provides new directions and opportunities for development of regimens for the prevention and treatment of prostate cancer. Important insight into the genetic/metabolic requirements of the prostate malignant process is now evolving. Most importantly at this time, an appreciation and recognition of the genetic/metabolic significance and implications in the development of prostate malignancy is imperative; and much needed research in this area is essential. Hopefully, this review will help to achieve these goals.

Minimally invasive pharmacokinetic and pharmacodynamic technologies in hypothesis-testing clinical trials of innovative therapies

Clinical trials of new cancer drugs should ideally include measurements of parameters such as molecular target expression, pharmacokinetic (PK) behavior, and pharmacodynamic (PD) endpoints that can be linked to measures of clinical effect. Appropriate PK/PD biomarkers facilitate proof-of-concept demonstrations for target modulation; enhance the rational selection of an optimal drug dose and schedule; aid decision-making, such as whether to continue or close a drug development project; and may explain or predict clinical outcomes. In addition, measurement of PK/PD biomarkers can minimize uncertainty associated with predicting drug safety and efficacy, reduce the high levels of drug attrition during development, accelerate drug approval, and decrease the overall costs of drug development. However, there are many challenges in the development and implementation of biomarkers that probably explain their disappointingly low implementation in phase I trials. The Pharmacodynamic/Pharmacokinetic Technologies Advisory committee of Cancer Research UK has found that submissions for phase I trials of new cancer drugs in the United Kingdom often lack detailed information about PK and/or PD endpoints, which leads to suboptimal information being obtained in those trials or to delays in starting the trials while PK/PD methods are developed and validated. Minimally invasive PK/PD technologies have logistic and ethical advantages over more invasive technologies. Here we review these technologies, emphasizing magnetic resonance spectroscopy and positron emission tomography, which provide detailed functional and metabolic information. Assays that measure effects of drugs on important biologic pathways and processes are likely to be more cost-effective than those that measure specific molecular targets. Development, validation, and implementation of minimally invasive PK/PD methods are encouraged.

High-resolution 3D MR spectroscopic imaging of the prostate at 3 T with the MLEV-PRESS sequence

A 3 T MLEV-point-resolved spectroscopy (PRESS) sequence employing optimized spectral-spatial and very selective outer-voxel suppression pulses was tested in 25 prostate cancer patients. At an echo time of 85 ms, the MLEV-PRESS sequence resulted in maximally upright inner resonances and minimal outer resonances of the citrate doublet of doublets. Magnetic resonance spectroscopic imaging (MRSI) exams performed at both 3 and 1.5 T for 10 patients demonstrated a 2.08+/-0.36-fold increase in signal-to-noise ratio (SNR) at 3 T as compared with 1.5 T for the center citrate resonances. This permitted the acquisition of MRSI data with a nominal spatial resolution of 0.16 cm3 at 3 T with similar SNR as the 0.34-cm3 data acquired at 1.5 T. Due to the twofold increase in spectral resolution at 3 T and the improved magnetic field homogeneity provided by susceptibility-matched endorectal coils, the choline resonance was better resolved from polyamine and creatine resonances as compared with 1.5 T spectra. In prostate cancer patients, the elevation of choline and the reduction of polyamines were more clearly observed at 3 T, as compared with 1.5 T MRSI. The increased SNR and corresponding spatial resolution obtainable at 3 T reduced partial volume effects and allowed improved detection of the presence and extent of abnormal metabolite levels in prostate cancer patients, as compared with 1.5 T MRSI.

Total-body MR-imaging in oncology

Although MRI is an effective modality in oncology, state-of-the-art total-body MRI (TB-MRI) in the past was infeasible in the diagnostic work-up, due to the need for repeated examinations with repositioning and separate surface coils to cover all body parts. To overcome this limitation, either a moving table platform in combination with the body-coil or a special designed rolling table platform with one body phased-array coil have been implemented with promising results for both tumor staging and metastases screening. Since 2004, state-of-the-art TB-MR imaging with high spatial resolution has become feasible using a newly developed 1.5 Tesla TB-MRI system with multiple receiver channels. This review gives an overview based on the recent literature as well as our own experience concerning the possibilities, challenges, and limitations of TB-MRI in oncology, emphasizing both oncological staging and early tumor detection in asymptomatic subjects.

[MR spectroscopic imaging for evaluation of prostate cancer]

MR spectroscopic imaging (MRSI) provides a noninvasive method of evaluating metabolic markers of prostate cancer or healthy prostatic tissue (the metabolites choline and citrate), and is performed in conjunction with high-resolution MR anatomic imaging. Multiple studies have showed the incremental role of MRSI combined with the anatomical information provided by MRI for assessment of cancer location and extent within the prostate, staging, and cancer aggressiveness. In addition, MRSI has a potential role for pre- and post-treatment evaluation in non surgical patients. Ongoing technical developments show the potential role of MRSI for guidance of biopsies or focal treatment. Further developments - including new 3T technology - will likely provide improved spectral resolution for better prostate cancer detection and characterization.

Mitochondrial aconitase and citrate metabolism in malignant and nonmalignant human prostate tissues

Background

In prostate cancer, normal citrate-producing glandular secretory epithelial cells undergo a metabolic transformation to malignant citrate-oxidizing cells. m-Aconitase is the critical step involved in this altered citrate metabolism that is essential to prostate malignancy. The limiting m-aconitase activity in prostate epithelial cells could be the result of a decreased level of m-aconitase enzyme and/or the inhibition of existing m-aconitase. Earlier studies identified zinc as an inhibitor of m-aconitase activity in prostate cells; and that the depletion of zinc in malignant cells is an important factor in this metabolic transformation. However, a possibility remains that an altered expression and level of m-aconitase enzyme might also be involved in this metabolic transformation. To address this issue, the in situ level of m-aconitase enzyme was determined by immunohistochemical analysis of prostate cancer tissue sections and malignant prostate cell lines.

Results

The immunocytochemical procedure successfully identified the presence of m-aconitase localized in the mitochondrial compartment in PC-3, LNCaP, and DU-145 malignant prostate cell lines. The examination of prostate tissue sections from prostate cancer subjects demonstrated that m-aconitase enzyme is present in the glandular epithelium of normal glands, hyperplastic glands, adenocrcinomatous glands, and prostatic intraepithelial neoplastic foci. Quantitative analysis of the relative level of m-aconitase in the glandular epithelium of citrate-producing adenomatous glands versus the citrate-oxidizing adenocarcinomatous glands revealed no significant difference in m-aconitase enzyme levels. This is in contrast to the down-regulation of ZIP1 zinc transporter in the malignant glands versus hyperplastic glands that exists in the same tissue samples.

Conclusion

The results demonstrate the existence of m-aconitase enzyme in the citrate-producing glandular epithelial cells; so that deficient m-aconitase enzyme is not associated with the limiting m-aconitase activity that prevents citrate oxidation in these cells. The level of m-aconitase is maintained in the malignant cells; so that an altered enzyme level is not associated with the increased m-aconitase activity. Consequently, the elevated zinc level that inhibits m-aconitase enzyme is responsible for the impaired citrate oxidation in normal and hyperplastic prostate glandular epithelial cells. Moreover, the down-regulation of ZIP1 zinc transporter and corresponding depletion of zinc results in the increase in the activity of the existing m-aconitase activity in the malignant prostate cells. The studies now define the mechanism for the metabolic transformation that characterizes the essential transition of normal citrate-producing epithelial cells to malignant citrate-oxidizing cells.

Quantification of prostate MRSI data by model-based time domain fitting and frequency domain analysis

This paper compares two spectral processing methods for obtaining quantitative measures from in vivo prostate spectra, evaluates their effectiveness, and discusses the necessary modifications for accurate results. A frequency domain analysis (FDA) method based on peak integration was compared with a time domain fitting (TDF) method, a model-based nonlinear least squares fitting algorithm. The accuracy of both methods at estimating the choline + creatine + polyamines to citrate ratio (CCP:C) was tested using Monte Carlo simulations, empirical phantom MRSI data and in vivo MRSI data. The paper discusses the different approaches employed to achieve the quantification of the overlapping choline, creatine and polyamine resonances. Monte Carlo simulations showed induced biases on the estimated CCP:C ratios. Both methods were successful in identifying tumor tissue, provided that the CCP:C ratio was greater than a given (normal) threshold. Both methods predicted the same voxel condition in 94% of the in vivo voxels (68 out of 72). Both TDF and FDA methods had the ability to identify malignant voxels in an artifact-free case study using the estimated CCP:C ratio. Comparing the ratios estimated by the TDF and the FDA, the methods predicted the same spectrum type in 17 out of 18 voxels of the in vivo case study (94.4%).

Correlation between metabolite ratios and ADC values of prostate in men with increased PSA level

Proton magnetic resonance spectroscopic imaging (MRSI) and diffusion-weighted imaging (DWI) were carried out in men with increased prostate-specific antigen (PSA) level. Forty subjects [controls (Group I) and patients (Groups II and III with PSA >20 and 4-20 ng/ml, respectively)] were investigated using endorectal coil at 1.5 T prior to transrectal ultrasound (TRUS)-guided biopsy. Metabolite ratio [citrate/(choline+creatine)] and apparent diffusion coefficient (ADC) were calculated for identical voxels. In patients, voxels that showed lower metabolite ratio showed reduced ADC in the peripheral zone (PZ) of the prostate, and voxels with increased metabolite ratio showed higher ADC. Metabolite ratios were used to predict areas of malignancy if the ratio was <1.4 and if ADC value was <1.17 x 10(-3) mm(2)/s. Patients in Group II had lower metabolite ratio and ADC in the PZ compared to controls and Group III. All 13 were positive for malignancy in MR, while 12 of 13 were positive on TRUS-guided sextant biopsy. In Group III, certain voxels of PZ that showed reduced metabolite ratio also showed lower ADC. A positive correlation was observed between metabolite ratio and ADC. MR predicted areas of malignancy in PZ in 15 of 20 patients; however, only six were positive on TRUS-guided biopsy perhaps due to high false-negative rate of TRUS-guided biopsy. Results show positive correlation between MRSI and DWI and their potential in detection of malignancy, thereby improving the diagnosis especially in patients with PSA level of 4-20 ng/ml.

'Omics'-based imaging in cancer detection and therapy

Genomics, proteomics and metabolomics, which can be also summarized as 'omics', have become increasingly inter-related with imaging. Gene expression profiling may be assessed using high-density microarrays for the detection of overexpression patterns, followed by the development of histochemical assays. Next, antibodies to the gene-corresponding proteins (for example, receptors) can be produced, leading to serum immunoassays for follow-up, as well as antibody-guided in vivo imaging or therapy. In vivo imaging for cancer detection and/or therapy can be performed by applying nonlabeled antibodies, by using radiolabeled antibodies for detection using single-photon tomography or positron emission tomography (PET), or by other tracers, for example, for magnetic resonance imaging tomography (MRI, MRT). Protein profiles from protein chips can be derived from mass maps obtained through mass spectrometry (MS). Electrophoretic separation of proteins has also been combined with MS to produce a two-dimensional assignment of proteins within a complex mixture. Overexpression of tumor-related proteins can be used for the development of antibodies to develop noninvasive assays that can be used in the screening of risk groups as a basis for further investigation by invasive imaging methods. Metabolomic profiling by nuclear magnetic resonance spectroscopy can be applied for the detection of biomarkers of the metabolome. Metabolite profiles in cells, tissues, and organisms can be generated with nuclear magnetic resonance spectroscopy and MS. Metabolic information provided by magnetic resonance spectroscopic imaging (MRSI) combined with the anatomical information provided by MRI can significantly improve the assessment of cancer location and extent, and cancer aggressiveness. Biomarkers found by MRSI can lead to new PET tracers. This article provides examples and discusses some of the recent achievements to bring forward novel strategies for the diagnosis and therapy of cancer.

Registration of MR prostate images with biomechanical modeling and nonlinear parameter estimation

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) have been shown to be very useful for identifying prostate cancers. For high sensitivity, the MRI/MRSI examination is often acquired with an endorectal probe that may cause a substantial deformation of the prostate and surrounding soft tissues. Such a probe is removed prior to radiation therapy treatment. To register diagnostic probe-in magnetic resonance (MR) images to therapeutic probe-out MR images for treatment planning, a new deformable image registration method is developed based on biomechanical modeling of soft tissues and estimation of uncertain tissue parameters using nonlinear optimization. Given two-dimensional (2-D) segmented probe-in and probe-out images, a finite element method (FEM) is used to estimate the deformation of the prostate and surrounding tissues due to displacements and forces resulting from the endorectal probe. Since FEM requires tissue stiffness properties and external force values as input, the method estimates uncertain parameters using nonlinear local optimization. The registration method is evaluated using images from five balloon and five rigid endorectal probe patient cases. It requires on average 37 s of computation time on a 1.6 GHz Pentium-M PC. Comparing the prostate outline in deformed probe-out images to corresponding probe-in images, the method obtains a mean Dice Similarity Coefficient (DSC) of 97.5% for the balloon probe cases and 98.1% for the rigid probe cases. The method improves significantly over previous methods (P < 0.05) with greater improvement for balloon probe cases with larger tissue deformations.

Zinc and prostate cancer: a critical scientific, medical, and public interest issue (United States)

The role of zinc in the development and progression of prostate malignancy and its potential application in the prevention and treatment of prostate cancer (PCa) are contemporary critical issues for the medical/scientific community and the public-at-large. The overwhelming clinical and experimental evidence provides a compelling rational basis for the expectation and concept that prostate zinc accumulation is an important factor in the development and progression of prostate malignancy; and that zinc could be efficacious in the prevention and treatment of PCa. In contrast, various epidemiologic studies have produced divergent and conflicting results regarding the efficacy of dietary and supplemental zinc against PCa. Before reaching any definitive conclusions regarding this complex issue, one should have a complete understanding of the clinical and experimental evidence associated with the involvement of zinc in the normal and malignant prostate. Also, an understanding of interacting effects of confounding factors on the absorption, assimilation, and bioavailability of supplemental dietary zinc is important. The purpose of this review is to present the current state of the clinical and experimental information regarding zinc relationships in the normal prostate and in the pathogenesis PCa. The evidence in support of a potential beneficial effect of zinc supplement versus potential harmful effects on PCa is assessed. A discussion of the divergent results of the epidemiologic studies is presented along with a description of important factors and conditions that impact or mask the effects of dietary zinc on PCa development and progression. We also hope to bring more attention to the medical and research community of the critical need for concerted clinical and basic research regarding zinc and PCa, for the development of appropriate human prostate models to investigate these relationships, for further appropriately designed epidemiologic studies, and for future well-controlled clinical trials.

Proton spectroscopy provides accurate pathology on biopsy and in vivo

In the last 25 years, MR spectroscopy (MRS) has moved from being a basic research tool into routine clinical use. The spectroscopy method reports on those chemicals that are mobile on the MR time scale. Many of these chemicals reflect specific pathological processes but are complicated by the fact that many chemicals change at one time. There are currently two clinical applications for spectroscopy. The first is in the pathology laboratory, where it can be an adjunct to, and in some cases replacement, for difficult pathologies like Barrett's esophagus and follicular adenoma of the thyroid. The spectroscopy method on a breast biopsy can also report on prognostic indicators, including the potential for spread, from information present in the primary tumor alone. The second application for spectroscopy is in vivo to provide a preoperative diagnosis and this is now achievable for several organs including the prostate. The development of spectroscopy for clinical purposes has relied heavily on the serially-sectioned histopathology to confirm the high accuracy of the method. The combination of in vivo MRI, in vivo MRS, and ex vivo MRS on biopsy samples offers a modality of very high accuracy for preoperative diagnosis and provision of prognostic information for human cancers.

Translational molecular imaging for cancer

Although most clinical diagnostic imaging studies employ anatomic techniques such as computed tomography (CT) and magnetic resonance (MR) imaging, much of radiology research currently focuses on adapting these conventional methods to physiologic imaging as well as on introducing new techniques and probes for studying processes at the cellular and molecular levels in vivo, i.e. molecular imaging. Molecular imaging promises to provide new methods for the early detection of cancer and support for personalized cancer therapy. Although molecular imaging has been practiced in various incarnations for over 20 years in the context of nuclear medicine, other imaging modalities have only recently been applied to the noninvasive assessment of physiology and molecular events. Nevertheless, there has been sufficient experience with specifically targeted contrast agents and high-resolution techniques for MR imaging and other modalities that we must begin moving these new technologies from the laboratory to the clinic. This brief review outlines several of the more promising areas of pursuit in molecular imaging for oncology with an emphasis on those that show the most immediate likelihood for clinical translation.

Expandable and rigid endorectal coils for prostate MRI: Impact on prostate distortion and rigid image registration

Endorectal coils (ERCs) are used for acquiring high spatial resolution magnetic resonance (MR) images of the human prostate. The goal of this study is to determine the impact of an expandable versus a rigid ERC on changes in the location and deformation of the prostate gland and subsequently on registering prostate images acquired with and without an ERC. Sagittal and axial T2 weighted MR images were acquired from 25 patients receiving a combined MR imaging/MR spectroscopic imaging staging exam for prostate cancer. Within the same exam, images were acquired using an external pelvic phased array coil both alone and in combination with either an expandable ERC (MedRad, Pittsburgh, PA) or a rigid ERC (USA Instruments, Aurora, OH). Rotations, translations and deformations caused by the ERC were measured and compared. The ability to register images acquired with and without the ERC using a manual rigid-body registration was assessed using a similarity index (SI). Both ERCs caused the prostate to tilt anteriorly with an average tilt of 18.5 degrees (17.4 +/- 9.9 and 19.5 +/- 11.3 degrees, mean +/- standard deviation, for expandable and rigid ERC, respectively). However, the expandable coil caused a significantly larger distortion of the prostate as compared to the rigid coil; compressing the prostate in the anterior/posterior direction by 4.1 +/- 3.0 mm vs 1.2 +/- 2.2 mm (14.5% vs 4.8%) (p < 0.0001), and widening the prostate in the right/left direction by 3.8 +/- 3.7 mm vs 1.5 +/- 3.1 mm (8.3% vs 3.4%) (p = 0.004). Additionally, the ability to manually align prostate images acquired with and without ERC was significantly (p < 0.0001) better for the rigid coil (SI = 0.941 +/- 0.008 vs 0.899 +/- 0.033, for the rigid and expandable coils, respectively). In conclusion, the manual rigid-body alignment of prostate MR images acquired with and without the ERC can be improved through the use of a rigid ERC.

Expanding the use of magnetic resonance in the assessment of tumor response to therapy: workshop report

Although dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and magnetic resonance spectroscopy (MRS) have great potential to provide routine assessment of cancer treatment response, their widespread application has been hampered by a lack of standards for use. Thus, the National Cancer Institute convened a workshop to assess developments and applications of these methods, develop standards for methodology, and engage relevant partners (drug and device industries, researchers, clinicians, and government) to encourage sharing of data and methodologies. Consensus recommendations were reached for DCE-MRI methodologies and the focus for initial multicenter trials of MRS. In this meeting report, we outline the presentations, the topics discussed, the ongoing challenges identified, and the recommendations made by workshop participants for the use of DCE-MRI and 1H MRS in the clinical assessment of antitumor therapies.

Magnetic resonance in surgical oncology: II - literature review

Ex vivo and in vivo applications of magnetic resonance spectroscopy have been developed which aid in distinguishing malignant from normal tissues. Studies of breast, colon, cervix, oesophageal and prostate cancer reveal both the successes and failings of present technology. Verification that these non-invasive tests might supplant conventional histology in obtaining spatial diagnostic and chemical prognostic information remains for the time being illusive.

Prostatic biopsy directed with endorectal MR spectroscopic imaging findings in patients with elevated prostate specific antigen levels and prior negative biopsy findings: early experience

PURPOSE

To prospectively evaluate the accuracy of transrectal ultrasonography (US)-guided biopsy directed with magnetic resonance (MR) spectroscopic imaging in patients with an elevated prostate specific antigen (PSA) level and negative findings at prior biopsy by using subsequent biopsy results as the reference standard.

MATERIALS AND METHODS

The committee on human research approved this study, and written informed consent was obtained. MR imaging and MR spectroscopic imaging were performed in 42 men (age range, 45-75 years; average age, 63.3 years; median age, 65 years) with negative findings at two or more prostatic biopsies and at digital rectal examination. MR spectroscopic data were rated on a scale of 1 (benign) to 5 (malignant) on the basis of standardized metabolic criteria. Abnormal voxels were overlaid on the corresponding transverse transrectal US images and used to perform voxel-guided biopsy of the prostate. All patients subsequently received an extended-pattern biopsy scheme.

RESULTS

Thirty-one of 42 patients demonstrated metabolic abnormalities that were suspicious for cancer (voxels with scores > or = 4). Eleven patients with negative MR spectroscopic imaging results also had negative biopsy findings. Cancer was detected in 17 (55%) of 31 men with positive MR spectroscopic imaging findings (voxels with scores > or = 4) with a sensitivity of 100%, specificity of 44%, positive predictive value of 55%, negative predictive value of 100%, and accuracy of 67%. In men with at least one spectroscopic voxel with a score of 5 (12 of 17 men), the sensitivity, specificity, positive and negative predictive values, and accuracy were 71%, 84%, 75%, 81%, and 79%, respectively.

CONCLUSION

Metabolic data from MR spectroscopic imaging can be transferred to transrectal US images and used to sample regions of cancer in men with rising PSA levels and negative findings at prior biopsy with good accuracy.

MR-guided interventional procedures: a review

Magnetic resonance imaging (MRI) has emerged as a potential guidance tool for a variety of procedures. Diagnostic and therapeutic procedures using either open surgical or percutaneous access are performed. They span from simple lesion targeting and biopsy to complex applications requiring multiple tasks performed simultaneously or in rapid succession. These tasks include instrument guidance and therapy monitoring as well as procedural follow-up. The interventional use of MRI (IMRI) is increasing steadily. This article reviews the prerequisites, systems, and clinical interventional procedures of IMRI.