(1)H MR spectroscopic imaging of the prostate at 7T using spectral-spatial pulses

PURPOSE

To assess the feasibility of prostate (1)H MR spectroscopic imaging (MRSI) using low-power spectral-spatial (SPSP) pulses at 7T, exploiting accurate spectral selection and spatial selectivity simultaneously.

METHODS

A double spin-echo sequence was equipped with SPSP refocusing pulses with a spectral selectivity of 1 ppm. Three-dimensional prostate (1)H-MRSI at 7T was performed with the SPSP-MRSI sequence using an 8-channel transmit array coil and an endorectal receive coil in three patients with prostate cancer and in one healthy subject. No additional water or lipid suppression pulses were used.

RESULTS

Prostate (1)H-MRSI could be obtained well within specific absorption rate (SAR) limits in a clinically feasible time (10 min). Next to the common citrate signals, the prostate spectra exhibited high spermine signals concealing creatine and sometimes also choline. Residual lipid signals were observed at the edges of the prostate because of limitations in spectral and spatial selectivity.

CONCLUSION

It is possible to perform prostate (1)H-MRSI at 7T with a SPSP-MRSI sequence while using separate transmit and receive coils. This low-SAR MRSI concept provides the opportunity to increase spatial resolution of MRSI within reasonable scan times.

Image quality and cancer visibility of T2-weighted magnetic resonance imaging of the prostate at 7 Tesla

OBJECTIVES

To assess the image quality of T2-weighted (T2w) magnetic resonance imaging of the prostate and the visibility of prostate cancer at 7 Tesla (T).

MATERIALS & METHODS

Seventeen prostate cancer patients underwent T2w imaging at 7T with only an external transmit/receive array coil. Three radiologists independently scored images for image quality, visibility of anatomical structures, and presence of artefacts. Krippendorff's alpha and weighted kappa statistics were used to assess inter-observer agreement. Visibility of prostate cancer lesions was assessed by directly linking the T2w images to the confirmed location of prostate cancer on histopathology.

RESULTS

T2w imaging at 7T was achievable with 'satisfactory' (3/5) to 'good' (4/5) quality. Visibility of anatomical structures was predominantly scored as 'satisfactory' (3/5) and 'good' (4/5). If artefacts were present, they were mostly motion artefacts and, to a lesser extent, aliasing artefacts and noise. Krippendorff's analysis revealed an α = 0.44 between three readers for the overall image quality scores. Clinically significant cancer lesions in both peripheral zone and transition zone were visible at 7T.

CONCLUSION

T2w imaging with satisfactory to good quality can be routinely acquired, and cancer lesions were visible in patients with prostate cancer at 7T using only an external transmit/receive body array coil.

KEY POINTS

• Satisfactory to good T2-weighted image quality of the prostate is achievable at 7T. • Periprostatic lipids appear hypo-intense compared to healthy peripheral zone tissue at 7T. • Prostate cancer is visible on T2-weighted MRI at 7T.

(31) P MR spectroscopic imaging of the human prostate at 7 T: T1 relaxation times, Nuclear Overhauser Effect, and spectral characterization

PURPOSE

Optimization of phosphorus ((31) P) MR spectroscopic imaging (MRSI) of the human prostate at 7 T by the evaluation of T1 relaxation times and the Nuclear Overhauser Effect (NOE) of phosphorus-containing metabolites.

METHODS

Twelve patients with prostate cancer and one healthy volunteer were scanned on a 7 T whole-body system using a (31) P endorectal coil combined with an eight-channel (1) H body array coil. T1 relaxation times were measured using progressive saturation in a two-dimensional localization sequence. (31) P MRSI was performed twice: once without NOE and once with NOE using low-power continuous wave (1) H irradiation to determine NOE enhancements.

RESULTS

T1 relaxation times of (31) P metabolites in the human prostate at 7 T varied between 3.0 and 8.3 s. Positive but variable NOE enhancements were measured for most metabolites. Remarkably, the (31) P MR spectra showed two peaks in chemical shift range of inorganic phosphate.

CONCLUSION

Knowledge of T1 relaxation times and NOE enhancements enables protocol optimization for (31) P MRSI of the prostate at 7 T. With a strongly reduced (31) P flip angle (≤ 45°), a (31) P MRSI dataset with optimal signal-to-noise ratio per unit time can be obtained within 15 minutes. The NOE enhancement can improve fitting accuracy, but its variability requires further investigation.

Clinical proton MR spectroscopy in central nervous system disorders

A large body of published work shows that proton (hydrogen 1 [(1)H]) magnetic resonance (MR) spectroscopy has evolved from a research tool into a clinical neuroimaging modality. Herein, the authors present a summary of brain disorders in which MR spectroscopy has an impact on patient management, together with a critical consideration of common data acquisition and processing procedures. The article documents the impact of (1)H MR spectroscopy in the clinical evaluation of disorders of the central nervous system. The clinical usefulness of (1)H MR spectroscopy has been established for brain neoplasms, neonatal and pediatric disorders (hypoxia-ischemia, inherited metabolic diseases, and traumatic brain injury), demyelinating disorders, and infectious brain lesions. The growing list of disorders for which (1)H MR spectroscopy may contribute to patient management extends to neurodegenerative diseases, epilepsy, and stroke. To facilitate expanded clinical acceptance and standardization of MR spectroscopy methodology, guidelines are provided for data acquisition and analysis, quality assessment, and interpretation. Finally, the authors offer recommendations to expedite the use of robust MR spectroscopy methodology in the clinical setting, including incorporation of technical advances on clinical units.

Metabolite ratios in 1H MR spectroscopic imaging of the prostate

In (1)H MR spectroscopic imaging ((1)H-MRSI) of the prostate the spatial distribution of the signal levels of the metabolites choline, creatine, polyamines, and citrate are assessed. The ratio of choline (plus spermine as the main polyamine) plus creatine over citrate [(Cho+(Spm+)Cr)/Cit] is derived from these metabolites and is used as a marker for the presence of prostate cancer. In this review, the factors that are of importance for the metabolite ratio are discussed. This is relevant, because the appearance of the metabolites in the spectrum depends not only on the underlying anatomy, metabolism, and physiology of the tissue, but also on acquisition parameters. These parameters influence especially the spectral shapes of citrate and spermine resonances, and consequently, the (Cho+(Spm+)Cr)/Cit ratio. Both qualitative and quantitative approaches can be used for the evaluation of (1)H-MRSI spectra of the prostate. For the quantitative approach, the (Cho+(Spm+)Cr)/Cit ratio can be determined by integration or by a fit based on model signals. Using the latter, the influence of the acquisition parameters on citrate can be taken into account. The strong overlap between the choline, creatine, and spermine resonances complicates fitting of the individual metabolites. This overlap and (unknown, possibly tissue-related) variations in T1, T2, and J-modulation hamper the application of corrections needed for a "normalized" (Cho+(Spm+)Cr)/Cit ratio that would enable comparison of spectra measured with different prostate MR spectroscopy protocols. Quantitative (Cho+(Spm+)Cr)/Cit thresholds for the evaluation of prostate cancer are therefore commonly established per institution or per protocol. However, if the same acquisition and postprocessing protocol were used, the ratio and the thresholds would be institution-independent, promoting the clinical usability of prostate (1)H-MRSI.

Mapping of prostate cancer by 1H MRSI

In many studies, it has been demonstrated that (1)H MRSI of the human prostate has great potential to aid prostate cancer management, e.g. in the detection and localisation of cancer foci in the prostate or in the assessment of its aggressiveness. It is particularly powerful in combination with T2 -weighted MRI. Nevertheless, the technique is currently mainly used in a research setting. This review provides an overview of the state-of-the-art of three-dimensional MRSI, including the specific hardware required, dedicated data acquisition sequences and information on the spectral content with background on the MR-visible metabolites. In clinical practice, it is important that relevant MRSI results become available rapidly, reliably and in an easy digestible way. However, this functionality is currently not fully available for prostate MRSI, which is a major obstacle for routine use by inexperienced clinicians. Routine use requires more automation in the processing of raw data than is currently available. Therefore, we pay specific attention in this review on the status and prospects of the automated handling of prostate MRSI data, including quality control. The clinical potential of three-dimensional MRSI of the prostate is illustrated with literature examples on prostate cancer detection, its localisation in the prostate, its role in the assessment of cancer aggressiveness and in the selection and monitoring of therapy.

Role of high-field MR in studies of localized prostate cancer

Magnetic resonance imaging is attracting increasing attention from the uroradiological community as a modality to guide the management of prostate cancer. With the high incidence of prostate cancer it might come as a surprise that for a very long time (and in many places even at present) treatment decisions were being made without the use of detailed anatomical and functional imaging of the prostate gland at hand. Although T2 -weighted MRI can provide great anatomical detail, by itself it is not specific enough to discriminate cancer from benign disease, so other functional MRI techniques have been explored to aid in detection, localization, staging and risk assessment of prostate cancer. With the current evolution of clinical MR systems from 1.5 to 3 T it is important to understand the advantages and the challenges of the higher magnetic field strength for the different functional MR techniques most used in the prostate: T2 -weighted MRI, diffusion-weighted MRI, MR spectroscopic imaging and dynamic contrast-enhanced imaging. In addition to this, the use of the endorectal coil at different field strengths is discussed in this review, together with an outlook of the possibilities of ultra-high-field MR for the prostate.

Feasibility of T2 -weighted turbo spin echo imaging of the human prostate at 7 tesla

PURPOSE

To demonstrate that high quality T2 -weighted (T2w) turbo spin-echo (TSE) imaging of the complete prostate can be achieved routinely and within safety limits at 7 T, using an external transceive body array coil only.

METHODS

Nine healthy volunteers and 12 prostate cancer patients were scanned on a 7 T whole-body system. Preparation consisted of B0 and radiofrequency shimming and localized flip angle calibration. T1 and T2 relaxation times were measured and used to define the T2w-TSE protocol. T2w imaging was performed using a TSE sequence (pulse repetition time/echo time 3000-3640/71 ms) with prolonged excitation and refocusing pulses to reduce specific absorption rate.

RESULTS

High quality T2w TSE imaging was performed in less than 2 min in all subjects. Tumors of patients with gold-standard tumor localization (MR-guided biopsy or prostatectomy) were well visualized on 7 T imaging (n = 3). The number of consecutive slices achievable within a 10-g averaged specific absorption rate limit of 10 W/kg was ≥28 in all subjects, sufficient for full prostate coverage with 3-mm slices in at least one direction.

CONCLUSION

High quality T2w TSE prostate imaging can be performed routinely and within specific absorption rate limits at 7 T with an external transceive body array.

Assessment of prostate cancer aggressiveness using dynamic contrast-enhanced magnetic resonance imaging at 3 T

BACKGROUND

A challenge in the diagnosis of prostate cancer (PCa) is the accurate assessment of aggressiveness.

OBJECTIVE

To validate the performance of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) of the prostate at 3 tesla (T) for the assessment of PCa aggressiveness, with prostatectomy specimens as the reference standard.

DESIGN, SETTINGS, AND PARTICIPANTS

A total of 45 patients with PCa scheduled for prostatectomy were included. This study was approved by the institutional review board; the need for informed consent was waived.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Subjects underwent a clinical MRI protocol including DCE-MRI. Blinded to DCE-images, PCa was indicated on T2-weighted images based on histopathology results from prostatectomy specimens with the use of anatomical landmarks for the precise localization of the tumor. PCa was classified as low-, intermediate-, or high-grade, according to Gleason score. DCE-images were used as an overlay on T2-weighted images; mean and quartile values from semi-quantitative and pharmacokinetic model parameters were extracted per tumor region. Statistical analysis included Spearman's ρ, the Kruskal-Wallis test, and a receiver operating characteristics (ROC) analysis.

RESULTS AND LIMITATIONS

Significant differences were seen for the mean and 75th percentile (p75) values of wash-in (p = 0.024 and p = 0.017, respectively), mean wash-out (p = 0.044), and p75 of transfer constant (K(trans)) (p = 0.035), all between low-grade and high-grade PCa in the peripheral zone. ROC analysis revealed the best discriminating performance between low-grade versus intermediate-grade plus high-grade PCa in the peripheral zone for p75 of wash-in, K(trans), and rate constant (Kep) (area under the curve: 0.72). Due to a limited number of tumors in the transition zone, a definitive conclusion for this region of the prostate could not be drawn.

CONCLUSIONS

Quantitative parameters (K(trans) and Kep) and semi-quantitative parameters (wash-in and wash-out) derived from DCE-MRI at 3 T have the potential to assess the aggressiveness of PCa in the peripheral zone. P75 of wash-in, K(trans), and Kep offer the best possibility to discriminate low-grade from intermediate-grade plus high-grade PCa.

In vivo (1) H MR spectroscopic imaging of aggressive prostate cancer: can we detect lactate?

PURPOSE

A semi-LASER sequence was optimized for in vivo lactate detection in the prostate.

METHODS

The ethical committee waived the need for informed consent to measure 17 patients with high grade prostate cancer on a 3T system. A semi-LASER sequence was used with an echo time of 144 ms and optimized interpulse timing for a spectral citrate shape with high signal intensity. An LCModel basis set was developed for fitting choline, creatine, spermine, citrate, and lactate and was used to fit all spectra in tumor-containing voxels. For patients without detectable lactate, the minimal detectable lactate concentration was determined by adding in all spectra of tumor tissue a simulated lactate signal. The amplitude of the simulated lactate signal was iteratively decreased until its fit reached a Cramér Rao lower bound >20%, which was then set as the patient-specific detection limit.

RESULTS

In none of the patients a convincing lactate signal was found. We estimated that on average the lactate levels in high grade prostate cancer are below 1.5 mM (range 0.9-3.5 mM), Interestingly, in one patient with extensive necrosis in the tumor biopsy samples (Gleason score 5+5), large lipid resonances were observed, which originated from the tumor.

CONCLUSION

The minimal detectable lactate concentration of 1.5 mM in high grade prostate cancer indicates that if lactate is increased it remains at low concentrations.

Quality control of prostate 1 H MRSI data

MRSI of prostate cancer provides a potential clinical tool to aid in the detection and characterisation of this disease, but its clinical use is limited by the need for the specialist training of radiologists to read these datasets. An essential part of this reading is the assessment of the usability and reliability of MRSI spectra because they can be affected by artefacts such as poor signal to noise, lipid signal contamination and broad resonances that could cause errors of interpretation. We have developed an automated quality control algorithm that classifies every voxel of an MRSI dataset as either acceptable or unacceptable for further analysis, based on the spectral profile alone. The method was trained and tested based on a gold standard of agreement of four experts. It was highly accurate: testing with a novel set of data from MRSI patients produced agreement with the experts' consensus decisions with a specificity of 0.95 and sensitivity of 0.95. This method provides fast quality control of three-dimensional MRSI datasets of the prostate, removing the need for radiologists to perform this time consuming, but necessary, task prior to further analysis.

Metabolic imaging of multiple x-nucleus resonances

This study describes a technique for fast imaging of x-nuclei metabolites. Due to increased sensitivity and larger chemical shift dispersion at high magnetic fields, images of multiple metabolites can be obtained simultaneously by selective excitation of their resonances with a multifrequency selective radiofrequency pulse at any desired flip angle. This aim is achieved by combining a three-dimensional gradient echo imaging sequence with a Shinnar-LeRoux optimized excitation pulse. A proper choice of bandwidth, imaging matrix size, and field of view allows using the chemical shift dispersion of the different resonances to completely separate their images within one large field of view. The method of fast metabolic imaging is illustrated with (13)C measurements of a phantom containing a solution of (13)C labeled glucose, lactate, and sodium octanoate and by dynamic measurements of the (31)P metabolites phosphocreatine and β-adenosine triphosphate in human femoral muscle in vivo, both at 7T. With dynamic selective (31)P imaging of the larger part of the upper leg, phosphocreatine signal intensity changes of specific muscles can be studied simultaneously by analyzing the sum of phosphocreatine signals within arbitrarily shaped regions of interest following the muscles' contours. This concept of dynamic metabolic imaging can be applied to other organs and further expanded to other MR-detectable nuclei and metabolites.

Prostate cancer aggressiveness: in vivo assessment of MR spectroscopy and diffusion-weighted imaging at 3 T

PURPOSE

To determine the individual and combined performance of magnetic resonance (MR) spectroscopic imaging and diffusion-weighted (DW) imaging at 3 T in the in vivo assessment of prostate cancer aggressiveness by using histopathologically defined regions of interest on radical prostatectomy specimens to define the prostate cancer regions to be investigated.

MATERIALS AND METHODS

The local institutional ethics review board approved this retrospective study and waived the informed consent requirement. Fifty-four patients with biopsy-proved prostate cancer underwent clinical MR spectroscopic imaging followed by prostatectomy. Guided by the histopathologic map, all spectroscopy voxels that contained tumor tissue were selected, and metabolite ratios (choline [Cho] plus creatine [Cr]-to-citrate [Cit] and Cho/Cr ratios) were derived. For each spectroscopic voxel, 25th percentile apparent diffusion coefficient (ADC) of the region corresponding to that voxel was determined, representing the most aberrant tumor part on the ADC map, which was often smaller than spectroscopic imaging voxels. Maximum metabolic ratios and minimum 25th percentile ADC of each tumor were related to tumor aggressiveness and were used to differentiate aggressiveness classes. A logistic regression model (LRM) was used to combine data from both modalities.

RESULTS

Significant correlation was found between aggressiveness classes and maximum Cho+Cr/Cit ratio (ρ=0.36), maximum Cho/Cr ratio (ρ=0.35), and minimum 25th percentile ADC (ρ=-0.63) in the peripheral zone (PZ). In the transition zone (TZ), the correlation was significant for only Cho+Cr/Cit and Cho/Cr ratios (ρ=0.58 and ρ=0.60, respectively). For differentiation between aggressiveness classes, LRM use did not result in significantly improved differentiation over any individual variables.

CONCLUSION

These findings enabled confirmation that MR spectroscopic imaging and DW imaging offer potential for in vivo noninvasive assessment of prostate cancer aggressiveness, and both modalities have comparable performance. The combination did not result in better performance. Nonetheless, the better performances of metabolite ratios in the TZ and of ADCs in the PZ suggest that they have complementary value.

Quantitative short echo time 1H MRSI of the peripheral edematous region of human brain tumors in the differentiation between glioblastoma, metastasis, and meningioma

PURPOSE

To assess metabolite levels in peritumoral edematous (PO) and surrounding apparently normal (SAN) brain regions of glioblastoma, metastasis, and meningioma in humans with (1)H-MRSI to find biomarkers that can discriminate between tumors and characterize infiltrative tumor growth.

MATERIALS AND METHODS

Magnetic resonance (MR) spectra (semi-LASER MRSI, 30 msec echo time, 3T) were selected from regions of interest (ROIs) under MRI guidance, and after quality control of MR spectra. Statistical testing between patient groups was performed for mean metabolite ratios of an entire ROI and for the highest value within that ROI.

RESULTS

The highest ratios of the level of choline compounds and the sum of myo-inositol and glycine over N-acetylaspartate and creatine compounds were significantly increased in PO regions of glioblastoma versus that of metastasis and meningioma. In the SAN region of glioblastoma some of these ratios were increased. Differences were less prominent for metabolite levels averaged over entire ROIs.

CONCLUSION

Specific metabolite ratios in PO and SAN regions can be used to discriminate glioblastoma from metastasis and meningioma. An analysis of these ratios averaged over entire ROIs and those with most abnormal values indicates that infiltrative tumor growth in glioblastoma is inhomogeneous and extends into the SAN region.

Imaging vascular function for early stage clinical trials using dynamic contrast-enhanced magnetic resonance imaging

Many therapeutic approaches to cancer affect the tumour vasculature, either indirectly or as a direct target. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has become an important means of investigating this action, both pre-clinically and in early stage clinical trials. For such trials, it is essential that the measurement process (i.e. image acquisition and analysis) can be performed effectively and with consistency among contributing centres. As the technique continues to develop in order to provide potential improvements in sensitivity and physiological relevance, there is considerable scope for between-centre variation in techniques. A workshop was convened by the Imaging Committee of the Experimental Cancer Medicine Centres (ECMC) to review the current status of DCE-MRI and to provide recommendations on how the technique can best be used for early stage trials. This review and the consequent recommendations are summarised here. Key Points • Tumour vascular function is key to tumour development and treatment • Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can assess tumour vascular function • Thus DCE-MRI with pharmacokinetic models can assess novel treatments • Many recent developments are advancing the accuracy of and information from DCE-MRI • Establishing common methodology across multiple centres is challenging and requires accepted guidelines.

Evaluation of a robotic technique for transrectal MRI-guided prostate biopsies

OBJECTIVES

To evaluate the accuracy and speed of a novel robotic technique as an aid to perform magnetic resonance image (MRI)-guided prostate biopsies on patients with cancer suspicious regions.

METHODS

A pneumatic controlled MR-compatible manipulator with 5 degrees of freedom was developed in-house to guide biopsies under real-time imaging. From 13 consecutive biopsy procedures, the targeting error, biopsy error and target displacement were calculated to evaluate the accuracy. The time was recorded to evaluate manipulation and procedure time.

RESULTS

The robotic and manual techniques demonstrated comparable results regarding mean targeting error (5.7 vs 5.8 mm, respectively) and mean target displacement (6.6 vs 6.0 mm, respectively). The mean biopsy error was larger (6.5 vs 4.4 mm) when using the robotic technique, although not significant. Mean procedure and manipulation time were 76 min and 6 min, respectively using the robotic technique and 61 and 8 min with the manual technique.

CONCLUSIONS

Although comparable results regarding accuracy and speed were found, the extended technical effort of the robotic technique make the manual technique - currently - more suitable to perform MRI-guided biopsies. Furthermore, this study provided a better insight in displacement of the target during in vivo biopsy procedures.

Prostate cancer: multiparametric MR imaging for detection, localization, and staging

This review presents the current state of the art regarding multiparametric magnetic resonance (MR) imaging of prostate cancer. Technical requirements and clinical indications for the use of multiparametric MR imaging in detection, localization, characterization, staging, biopsy guidance, and active surveillance of prostate cancer are discussed. Although reported accuracies of the separate and combined multiparametric MR imaging techniques vary for diverse clinical prostate cancer indications, multiparametric MR imaging of the prostate has shown promising results and may be of additional value in prostate cancer localization and local staging. Consensus on which technical approaches (field strengths, sequences, use of an endorectal coil) and combination of multiparametric MR imaging techniques should be used for specific clinical indications remains a challenge. Because guidelines are currently lacking, suggestions for a general minimal protocol for multiparametric MR imaging of the prostate based on the literature and the authors' experience are presented. Computer programs that allow evaluation of the various components of a multiparametric MR imaging examination in one view should be developed. In this way, an integrated interpretation of anatomic and functional MR imaging techniques in a multiparametric MR imaging examination is possible. Education and experience of specialist radiologists are essential for correct interpretation of multiparametric prostate MR imaging findings. Supportive techniques, such as computer-aided diagnosis are needed to obtain a fast, cost-effective, easy, and more reproducible prostate cancer diagnosis out of more and more complex multiparametric MR imaging data.

Reproducibility of 3D 1H MR spectroscopic imaging of the prostate at 1.5T

PURPOSE

To determine the reproducibility of 3D proton magnetic resonance spectroscopic imaging ((1)H-MRSI) of the human prostate in a multicenter setting at 1.5T.

MATERIALS AND METHODS

Fourteen subjects were measured twice with 3D point-resolved spectroscopy (PRESS) (1)H-MRSI using an endorectal coil. MRSI voxels were selected in the peripheral zone and combined central gland at the same location in the prostate in both measurements. Voxels with approved spectral quality were included to calculate Bland-Altman parameters for reproducibility from the choline plus creatine to citrate ratio (CC/C). The repeated spectroscopic data were also evaluated with a standardized clinical scoring system.

RESULTS

A total of 74 voxels were included for reproducibility analysis. The complete range of biologically interesting CC/C ratios was covered. The overall within-voxel standard deviation (SD) of the CC/C ratio of the repeated measurements was 0.13. This value is equal to the between-subject SD of noncancer prostate tissue. In >90% of the voxels the standardized clinical score did not differ relevantly between the measurements.

CONCLUSION

Repeated measurements of in vivo 3D (1)H-MRSI of the complete prostate at 1.5T produce equal and quantitative results. The reproducibility of the technique is high enough to provide it as a reliable tool in assessing tumor presence in the prostate.

Detection of fully refocused polyamine spins in prostate cancer at 7 T

(1)H MRSI is often used at 1.5 or 3 T to study prostate cancer, where the ratio of choline + creatine to citrate is taken as a marker for tumour presence. Recently, the level of polyamines (mainly spermine) has been shown to improve specificity even further. However, the in vivo detection of these polyamines (at 3.1  ppm) is hampered by signal cancellation as a result of J-coupling effects and signal overlap with choline (3.2  ppm) and creatine (3.0  ppm) resonances. At higher magnetic field strengths, the chemical shift dispersion will increase, which allows the use of very selective radiofrequency pulses to refocus J-coupled spins. In this work, we added selective refocusing pulses to a semi-LASER (localisation based on adiabatic selective refocusing) sequence at 7 T, and optimised the inter-pulse timings of the sequence for fully refocused detection of spermine spins, whilst maintaining optimised detection of choline, creatine and the strongly coupled spin system of citrate.

Feasibility of a pneumatically actuated MR-compatible robot for transrectal prostate biopsy guidance

PURPOSE

To assess the feasibility of using a remote-controlled, pneumatically actuated magnetic resonance (MR)-compatible robotic device to aid transrectal biopsy of the prostate performed with real-time 3-T MR imaging guidance.

MATERIALS AND METHODS

This prospective study was approved by the ethics review board, and written informed consent was obtained from all patients. Twelve consecutive men who were clinically suspected of having prostate cancer and had a history of at least one transrectal ultrasonography (US)-guided prostate biopsy with negative results underwent diagnostic multiparametric MR imaging of the prostate. Two radiologists in consensus identified cancer-suspicious regions (CSRs) in 10 patients. These regions were subsequently targeted with the robot for MR imaging-guided prostate biopsy. To direct the needle guide toward the CSRs, the MR-compatible robotic device was remote controlled at the MR console by means of a controller and a graphical user interface for real-time MR imaging guidance of the needle guide. The ability to reach the CSRs with the robot for biopsy was analyzed.

RESULTS

A total of 17 CSRs were detected in 10 patients at the diagnostic MR examinations. These regions were targeted for MR imaging-guided robot-assisted prostate biopsy. Thirteen (76%) of the 17 CSRs could be reached with the robot for biopsy. Biopsy of the remaining four CSRs was performed without use of the robot.

CONCLUSION

It is feasible to perform transrectal prostate biopsy with real-time 3-T MR imaging guidance with the aid of a remote-controlled, pneumatically actuated MR-compatible robotic device.

31P magnetic resonance spectroscopic imaging with polarisation transfer of phosphomono- and diesters at 3 T in the human brain: relation with age and spatial differences

Tissue levels of the compounds phosphocholine (PC), phosphoethanolamine (PE), glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) can be studied by in vivo 31P MRS. However, the detection of the signals of these compounds suffers from low sensitivity and contamination by underlying broad resonances of other phosphorylated compounds. Improved sensitivity without this contamination can be achieved with a method for optimal polarisation transfer of 1H to 31P spins in these molecules, called selective refocused insensitive nuclei-enhanced polarisation transfer (sRINEPT). The aim of this study was to implement a three-dimensional magnetic resonance spectroscopic imaging (MRSI) version of sRINEPT on a clinical 3 T magnetic resonance system to obtain spatially resolved relative levels of PC, PE, GPC and GPE in the human brain as a function of age, which could be used as a reference dataset for clinical applications. Good signal-to-noise ratios were obtained from voxels of 17 cm(3) of the parietal and occipital lobes of the brain within a clinically acceptable measurement time of 17 min. Eighteen healthy subjects of different ages (16-70 years) were examined with this method. A strong inverse relation of the PE/GPE and PC/GPC ratios with age was found. Spatial resolution was sufficient to detect differences in metabolite ratios between white and grey matter. Moreover, we showed the feasibility of this method for clinical use in a pilot study of patients with brain tumours. The sRINEPT MRSI technique enables the exploration of phospholipid metabolism in brain diseases with a better sensitivity than was possible with earlier 31P MRS methods.

In vivo 13C magnetic resonance spectroscopy of a human brain tumor after application of 13C-1-enriched glucose

OBJECTIVES

As a unique tool to assess metabolic fluxes noninvasively, (13)C magnetic resonance spectroscopy (MRS) could help to characterize and understand malignancy in human tumors. However, its low sensitivity has hampered applications in patients. The aim of this study was to demonstrate that with sensitivity-optimized localized (13)C MRS and intravenous infusion of [1-(13)C]glucose under euglycemia, it is possible to assess the dynamic conversion of glucose into its metabolic products in vivo in human glioma tissue.

MATERIALS AND METHODS

Measurements were done at 3 T with a broadband single RF channel and a quadrature (13)C surface coil inserted in a (1)H volume coil. A (1)H/(13)C polarization transfer sequence was applied, modified for localized acquisition, alternatively in two (50 ml) voxels, one encompassing the tumor and the other normal brain tissue.

RESULTS

After about 20 min of [1-(13)C]glucose infusion, a [3-(13)C]lactate signal appeared among several resonances of metabolic products of glucose in MR spectra of the tumor voxel. The resonance of [3-(13)C]lactate was absent in MR spectra from contralateral tissue. In addition, the intensity of [1-(13)C]glucose signals in the tumor area was about 50% higher than that in normal tissue, likely reflecting more glucose in extracellular space due to a defective blood-brain barrier. The signal intensity for metabolites produced in or via the tricarboxylic acid (TCA) cycle was lower in the tumor than in the contralateral area, albeit that the ratios of isotopomer signals were comparable.

CONCLUSION

With an improved (13)C MRS approach, the uptake of glucose and its conversion into metabolites such as lactate can be monitored noninvasively in vivo in human brain tumors. This opens the way to assessing metabolic activity in human tumor tissue.

Short echo time 1H MRSI of the human brain at 3T with adiabatic slice-selective refocusing pulses; reproducibility and variance in a dual center setting

PURPOSE

To assess the reproducibility of (1)H-MR spectroscopic imaging (MRSI) of the human brain at 3T with volume selection by a double spin echo sequence for localization with adiabatic refocusing pulses (semi-LASER).

MATERIALS AND METHODS

Twenty volunteers in two different institutions were measured twice with the same pulse sequence at an echo time of 30 msec. Magnetic resonance (MR) spectra were analyzed with LCModel with a simulated basis set including an experimentally acquired macromolecular signal profile. For specific regions in the brain mean metabolite levels, within and between subject variance, and the coefficient of variation (CoV) were calculated (for taurine, glutamate, total N-acetylaspartate, total creatine, total choline, myo-inositol + glycine, and glutamate + glutamine).

RESULTS

Repeated measurements showed no significant differences with a paired t-test and a high reproducibility (CoV ranging from 3%-30% throughout the selected volume). Mean metabolite levels and CoV obtained in similar regions in the brain did not differ significantly between two contributing institutions. The major source of differences between different measurements was identified to be the between-subject variations in the volunteers.

CONCLUSION

We conclude that semi-LASER (1)H-MRSI at 3T is an adequate method to obtain quantitative and reproducible measures of metabolite levels over large parts of the brain, applicable across multiple centers.

Proton spectroscopic imaging of the human prostate at 7 T

The sensitivity of proton MR Spectroscopic Imaging ((1)H-MRSI) of the prostate can be optimized by using the high magnetic field strength of 7 T in combination with an endorectal coil. In the work described in this paper we introduce an endorectal transceiver at 7 T, validate its safety for in vivo use and apply a pulse sequence, optimized for three-dimensional (3D) (1)H-MRSI of the human prostate at 7 T. A transmit/receive endorectal RF coil was adapted from a commercially available 3 T endorectal receive-only coil and validated to remain within safety guidelines for radiofrequency (RF) power deposition using numerical models, MR thermometry of phantoms, and in vivo temperature measurements. The (1)H-MRSI pulse sequence used adiabatic slice selective refocusing pulses and frequency-selective water and lipid suppression to selectively obtain the relevant metabolite signals from the prostate. Quantum mechanical simulations were used to adjust the inter-pulse timing for optimal detection of the strongly coupled spin system of citrate resulting in an echo time of 56 ms. Using this endorectal transceiver and pulse sequence with slice selective adiabatic refocusing pulses, 3D (1)H-MRSI of the human prostate is feasible at 7 T with a repetition time of 2 s. The optimized inter-pulse timing enables the absorptive detection of resonances of spins from spermine and citrate in phase with creatine and choline. These potential tumor markers may improve the in vivo detection, localization, and assessment of prostate cancer.

Quantitative MR imaging of individual muscle involvement in facioscapulohumeral muscular dystrophy

The purpose of this study was to implement a quantitative MR imaging method for the determination of muscular and fat content in individual skeletal muscles of patients with facioscapulohumeral muscular dystrophy (FSHD). Turbo Inversion Recovery Magnitude (TIRM) and multiecho MR images were acquired from seven FSHD patients and healthy volunteers. Signal decay in the multiecho MR images was fitted to a biexponential function with fixed relaxation rates for muscle and fat tissue and used to calculate the degree of fatty infiltration in eight muscles in the lower leg. Considerable differences in fatty infiltration between different muscles were observed in FSHD patients, suggesting that this could be used as a biomarker for disease progression. TIRM imaging indicated an inflammatory component of the disease previously only observed in muscle biopsies. Typically, muscle involvement was non-uniform even within one muscle, indicating that MRI can be used as a valuable tool to study pathophysiology and therapy evaluation in FSHD.

Efficient 1H to 31P polarization transfer on a clinical 3T MR system

31P MR spectroscopy (MRS) in the detection of phosphocholine (PC), glycerolphosphocholine (GPC), phosphorylelthanolamine (PE), and glycerolphosphoethanolamine (GPE) compounds has shown clinical potential at 1.5T for several human diseases. The use of (1)H to (31)P polarization transfer can improve the sensitivity using a refocused INEPT method with a potential enhancement of 2.4 (gamma(1H)/gamma(31P)). However, in this method the (31)P signals of PE, PC, GPE, and GPC are strongly attenuated (50% or more) due to J-coupling between (31)P and (1)H that have similar magnitudes for homonuclear J-coupling constants in those metabolites. A method to cancel the homonuclear J-coupling effects in polarization transfer experiments is to apply frequency-selective refocusing pulses, which becomes feasible at 3T due to the increased chemical shift dispersion as compared to 1.5T. In this study, full (1)H to (31)P polarization transfer was realized using chemical shift selective refocusing pulses at 3T. T(1) and T(2) values for (1)H and (31)P spins of PE, PC, GPE, and GPC were measured in the human brain. A more than 2-fold signal-to-noise ratio (SNR) improvement was obtained compared to an optimized direct (31)P MRS method. As shifted RF pulses were used, this method can be applied on a broadband clinical MR system with a single RF system.

Changes in prostate shape and volume and their implications for radiotherapy after introduction of endorectal balloon as determined by MRI at 3T

PURPOSE

To determine the changes in prostate shape and volume after the introduction of an endorectal coil (ERC) by means of magnetic resonance imaging (MRI) at 3T.

METHODS AND MATERIALS

A total of 44 consecutive patients with biopsy-proven prostate cancer underwent separate MRI examinations at 3T with a body array coil and subsequently with an ERC inflated with 50 mL of fluid. Prospectively, two experienced readers independently evaluated all data sets in random order. The maximal anteroposterior, right-to-left, and craniocaudal prostate diameters, as well as the total prostate and peripheral zone and central gland volumes were measured before and after ERC introduction. The changes in prostate shape and volume were analyzed using Wilcoxon's test for paired samples.

RESULTS

The introduction of the ERC significantly changed the prostate shape in all three directions, with mean changes in the anteroposterior, right-to-left, and craniocaudal diameters of 15.7% (5.5 mm), 7.7% (3.5 mm), and 6.3% (2.2 mm), respectively. The mean total prostate, peripheral zone, and central gland volume decreased significantly after ERC introduction by 17.9% (8.3 cm(3)), 21.6% (4.8 cm(3)), and 14.2% (3.4 cm(3)), respectively.

CONCLUSION

ERC introduction as observed by 3T MRI changed the prostate shape and volume significantly. The mean anteroposterior diameter was reduced by nearly one-sixth of its original diameter, and the mean total prostate volume was decreased by approximately 18%. This could cause difficulties and should be considered when using ERC-based MRI for MRI-computed tomography fusion and radiotherapy planning.

Short echo time 1H-MRSI of the human brain at 3T with minimal chemical shift displacement errors using adiabatic refocusing pulses

The chemical shift displacement error (CSDE) is an often-underestimated problem in slice selection for localized proton spectroscopy at higher fields. With the proposed semi-localized by adiabatic selective refocusing (LASER) pulse sequence, this problem is dealt with by using RF pulses with bandwidths in the order of 5 kHz. A combination of conventional nonadiabatic slice-selective excitation of proton spins, together with double slice-selective refocusing of the spins by two pairs of adiabatic full-passage (APF) pulses, produces a spin echo in a volume of interest (VOI) at an echo time down to 30 ms. An illustration of the CSDE of conventional point-resolved spectroscopy (PRESS) and the semi-LASER sequence is shown with a measurement of the brain of a volunteer at 3T. With one application of the technique to a patient with a glioblastoma multiforme (GBM), its clinical functionality is demonstrated. With sharp selection profiles and a small CSDE, voxels close to the edge of the VOI can also be used for evaluation. With the additional advantage of being relatively insensitive for B(1) inhomogeneities, the semi-LASER technique can be viewed as a superior substitute for conventional PRESS MR spectroscopic imaging (MRSI) at 3T and beyond.

Towards 1H-MRSI of the human brain at 7T with slice-selective adiabatic refocusing pulses

OBJECTIVE

To explore the possibilities of proton spectroscopic imaging (1H-MRSI) of the human brain at 7 Tesla with adiabatic refocusing pulses.

MATERIALS AND METHODS

A combination of conventional slice selective excitation and two pairs of slice selective adiabatic refocusing pulses (semi-LASER) results in the formation of an echo from a localized volume. Depending on the used radio frequency (rf) coil efficiency and available rf power, the duration of the adiabatic full passage pulses (AFPs) is adapted to enable echo times down to 50 ms (head coil) or 30 ms (local surface coil).

RESULTS

An AFP duration of 5 ms with a corresponding bandwidth of 5.1 kHz resulted in a chemical shift displacement error of 23% over 3.8 ppm at 7T. Using a local surface coil and an echo time down to 30 ms, we detected not only the three main metabolites (NAA, Cr and Cho), but also coupled signals from myo-inositol and glutamate/glutamine in spectra from 0.14 cc voxels with linewidths down to 10 Hz in 10 min measurement time.

CONCLUSIONS

The semi-LASER pulse sequence enables 1H-MRSI of the human brain at 7T for larger parts of the brain as well as small localized areas with both a high spectral and spatial resolution.

Three-dimensional Proton MR Spectroscopy of Human Prostate at 3 T without Endorectal Coil: Feasibility

PURPOSE

To evaluate sensitivity and specificity of proton magnetic resonance (MR) spectroscopy of the prostate with external surface coil elements at 3 T for differentiation of cancer from healthy tissue within an acceptable measurement time, by using histopathologic findings as the reference standard.

MATERIALS AND METHODS

The study was approved by the institutional review board; informed consent was obtained. Forty-five men (age range, 51-70 years) underwent 3-T MR imaging with external radiofrequency surface coils for signal reception. MR spectroscopy was performed with acquisition-weighted three-dimensional water- and lipid-suppressed point-resolved spectroscopy pulse sequence. Voxels were classified into healthy peripheral zone, central gland, and periurethral zone and cancer tissue. Cancer voxels were classified according to cancer size and certainty in matching histopathologic findings with MR images. After visual inspection of automated fitting of classified voxels, the choline plus creatine-to-citrate (Cho + Cr/Cit) ratio was calculated for all tissues. Area under the receiver operating characteristic curves (A(z)) values were used to assess accuracy of discrimination of cancer from healthy tissues. P < .05 indicated a significant difference.

RESULTS

After exclusion of four patients with no voxels that passed visual inspection of the automated fit, a median of 82% of the classified voxels per patient was used in the analysis. Mean Cho + Cr/Cit ratios for healthy tissues were 0.22 +/- 0.12 (standard deviation) for peripheral zone, 0.34 +/- 0.14 for central gland, and 0.36 +/- 0.20 for periurethral area; all were significantly different from that of cancer (P < .001). A(z) for discrimination of probable and definite cancer tissue from healthy tissue for the peripheral zone (0.84) was significantly higher than that for the central gland (0.69) (P < .05).

CONCLUSION

Three-dimensional proton MR spectroscopy of the prostate, with a combination of only external radiofrequency surface coils at 3 T, can be used to discriminate cancer from healthy tissue.

Prostate and lymph node proton magnetic resonance (MR) spectroscopic imaging with external array coils at 3 T to detect recurrent prostate cancer after radiation therapy

In a patient suspected of having recurrent prostate cancer after radiation therapy, we demonstrate the feasibility of noninvasive proton magnetic resonance spectroscopic (1H-MRS) imaging of the prostate and a lymph node at 3 T using a matrix of external surface coils. Written informed consent was obtained from the patient. With 1H-MRS imaging, high choline with low citrate signal was observed in the prostate, and in the lymph node a signal of choline-containing compounds was identified. The tissue level of the compounds in the enlarged lymph node was estimated to be 8.1 mmol/kg water. Subsequent histopathological analysis of systematic transrectal ultrasound-guided prostate biopsy and computed tomography-guided biopsy of the lymph node confirmed the presence of prostate cancer in both.

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.

Intact plant magnetic resonance imaging to study dynamics in long-distance sap flow and flow-conducting surface area

Due to the fragile pressure gradients present in the xylem and phloem, methods to study sap flow must be minimally invasive. Magnetic resonance imaging (MRI) meets this condition. A dedicated MRI method to study sap flow has been applied to quantify long-distance xylem flow and hydraulics in an intact cucumber (Cucumis sativus) plant. The accuracy of this MRI method to quantify sap flow and effective flow-conducting area is demonstrated by measuring the flow characteristics of the water in a virtual slice through the stem and comparing the results with water uptake data and microscopy. The in-plane image resolution of 120 x 120 microm was high enough to distinguish large individual xylem vessels. Cooling the roots of the plant severely inhibited water uptake by the roots and increased the hydraulic resistance of the plant stem. This increase is at least partially due to the formation of embolisms in the xylem vessels. Refilling the larger vessels seems to be a lengthy process. Refilling started in the night after root cooling and continued while neighboring vessels at a distance of not more than 0.4 mm transported an equal amount of water as before root cooling. Relative differences in volume flow in different vascular bundles suggest differences in xylem tension for different vascular bundles. The amount of data and detail that are presented for this single plant demonstrates new possibilities for using MRI in studying the dynamics of long-distance transport in plants.

Standardized threshold approach using three-dimensional proton magnetic resonance spectroscopic imaging in prostate cancer localization of the entire prostate

OBJECTIVES

We sought to determine the localization accuracy using 3-dimensional (3D) proton magnetic resonance spectroscopic imaging (MRSI) of the entire prostate with a standardized thresholds approach in prostate cancer patients.

MATERIALS AND METHODS

In a prospective study, 32 consecutive patients were examined. Mean age and prostate specific antigen level were 61 years and 7.8 ng/mL, respectively. Median biopsy Gleason score was 6. T2-weighted MRI and 3D MRSI of the entire prostate were performed. Three readers recorded the location of suspicious peripheral zone and central gland cancer nodules on a standardized division of the prostate (14 regions of interest [ROI]) using a standardized thresholds approach. The degree of diagnostic confidence for each ROI was recorded on a 5-point scale. Reconstructed whole-mount section histopathology was the standard of reference. The sensitivity, specificity, positive, and negative predictive value, overall accuracy and interobserver agreement were calculated. Areas under the ROI-based receiver operating characteristic curve (AUC) and diagnostic performance parameters were determined.

RESULTS

The standardized thresholds approach had an accuracy of 81% and an AUC of 0.85-0.86 for differentiation between benign and malignant ROIs in the peripheral zone and an accuracy of 87% and an AUC of 0.86-0.91 for this differentiation in the central gland, respectively. Specificities of 81% to 88% were achieved with accompanying sensitivities of 75% to 92% for both peripheral zone and central gland, respectively. Moderate to near-perfect interobserver agreement was demonstrated (kappa=0.42-0.91).

CONCLUSION

Our data indicate that a standardized zone-specific threshold approach in MRSI of the prostate is able to prospectively differentiate between benign and malignant tissues in the peripheral zone and the central gland with good accuracy and interobserver agreement.

Sensitivity of magnetic resonance imaging of dendritic cells for in vivo tracking of cellular cancer vaccines

Success of immunotherapy with dendritic cells (DC) to treat cancer is highly dependent on their interaction with and activation of antigen specific T cells. To maximize DC-T cell contact accurate delivery of the therapeutic cells into the lymph node, or efficient trafficking of DC to the lymph nodes of the patient is essential. Since responses are seen in some patients but not in others, monitoring of the injected cells may be of major importance. Tracking of cells with magnetic resonance (MR) imaging is a non-invasive method that provides detailed anatomical information and is therefore more informative for the evaluation of the localization of therapeutic cells after injection than e.g. scintigraphic imaging. To challenge the sensitivity of this novel technique, we investigated the minimum amount of label and the number of cells required for MR imaging and the effect of labeling on DC function. DC were labeled with different concentrations of a clinically approved MR contrast agent consisting of superparamagnetic iron oxide particles and were imaged at both 3 and 7 T. Our results demonstrate the following: (i) When loaded with 30 (+/-4) pg Fe/cell, cell numbers as low as 1,000 cells/mm3 at 3 T and 500 cells/mm3 at 7 T could be readily imaged; (ii) Labeling does not affect cell viability and function; (iii) Because of its high spatial resolution and sensitivity, MRI is ideally suited to track therapeutic cells in vivo.

Prostate cancer localization with dynamic contrast-enhanced MR imaging and proton MR spectroscopic imaging

PURPOSE

To prospectively determine the accuracies of T2-weighted magnetic resonance (MR) imaging, dynamic contrast material-enhanced MR imaging, and quantitative three-dimensional (3D) proton MR spectroscopic imaging of the entire prostate for prostate cancer localization, with whole-mount histopathologic section findings as the reference standard.

MATERIALS AND METHODS

This study was approved by the institutional review board, and informed consent was obtained from all patients. Thirty-four consecutive men with a mean age of 60 years and a mean prostate-specific antigen level of 8 ng/mL were examined. The median biopsy Gleason score was 6. T2-weighted MR imaging, dynamic contrast-enhanced MR imaging, and 3D MR spectroscopic imaging were performed, and on the basis of the image data, two readers with different levels of experience recorded the location of the suspicious peripheral zone and central gland tumor nodules on each of 14 standardized regions of interest (ROIs) in the prostate. The degree of diagnostic confidence for each ROI was recorded on a five-point scale. Localization accuracy and ROI-based receiver operating characteristic (ROC) curves were calculated.

RESULTS

For both readers, areas under the ROC curve for T2-weighted MR, dynamic contrast-enhanced MR, and 3D MR spectroscopic imaging were 0.68, 0.91, and 0.80, respectively. Reader accuracy in tumor localization with dynamic contrast-enhanced imaging was significantly better than that with quantitative spectroscopic imaging (P < .01). Reader accuracy in tumor localization with both dynamic contrast-enhanced imaging and spectroscopic imaging was significantly better than that with T2-weighted imaging (P < .01).

CONCLUSION

Compared with use of T2-weighted MR imaging, use of dynamic contrast-enhanced MR imaging and 3D MR spectroscopic imaging facilitated significantly improved accuracy in prostate cancer localization.

Prostate cancer evaluated with ferumoxtran-10-enhanced T2*-weighted MR Imaging at 1.5 and 3.0 T: early experience

PURPOSE

To prospectively evaluate the feasibility of ferumoxtran-10-enhanced magnetic resonance (MR) imaging at high magnetic field strength (3.0 T) and to compare image quality between 1.5- and 3.0-T MR imaging in terms of lymph node detection in patients with prostate cancer.

MATERIALS AND METHODS

This study was institutional review board approved, and all patients gave written informed consent. Forty-eight consecutive patients aged 51-79 years (mean, 65.5 years) with prostate cancer were enrolled. T2*-weighted 1.5- and 3.0-T MR images of the pelvis were acquired in a sagittal plane parallel to the psoas muscle 24 hours after ferumoxtran-10 administration. A pelvic and body phased-array coil was used and yielded an in-plane resolution of 0.56 x 0.56 x 3.00 mm at 1.5 T and 0.50 x 0.50 x 2.50 mm at 3.0 T. All images were evaluated by three readers for total image quality, lymph node border delineation, muscle-fat contrast, and vessel-fat contrast. Statistical significance was calculated by using the Mann-Whitney U test. Subsequently, the general linear mixed model was used to estimate the contributions of three factors-patient, reader, and technique-to the variability of the imaging results.

RESULTS

Significantly (P < .05) better muscle-fat contrast, vessel-fat contrast, lymph node border delineation, and total image quality were observed at 3.0-T MR imaging. The general linear mixed model revealed that the variability of all results could be attributed to the use of 3.0-T imaging.

CONCLUSION

Ferumoxtran-10-enhanced MR imaging can be performed at high magnetic field strengths and result in improved image quality, which may lead to improved detection of small positive lymph nodes.

IMRT boost dose planning on dominant intraprostatic lesions: Gold marker-based three-dimensional fusion of CT with dynamic contrast-enhanced and 1H-spectroscopic MRI

PURPOSE

To demonstrate the theoretical feasibility of integrating two functional prostate magnetic resonance imaging (MRI) techniques (dynamic contrast-enhanced MRI [DCE-MRI] and 1H-spectroscopic MRI [MRSI]) into inverse treatment planning for definition and potential irradiation of a dominant intraprostatic lesion (DIL) as a biologic target volume for high-dose intraprostatic boosting with intensity-modulated radiotherapy (IMRT).

METHODS AND MATERIALS

In 5 patients, four gold markers were implanted. An endorectal balloon was inserted for both CT and MRI. A DIL volume was defined by DCE-MRI and MRSI using different prostate cancer-specific physiologic (DCE-MRI) and metabolic (MRSI) parameters. CT-MRI registration was performed automatically by matching three-dimensional gold marker surface models with the iterative closest point method. DIL-IMRT plans, consisting of whole prostate irradiation to 70 Gy and a DIL boost to 90 Gy, and standard IMRT plans, in which the whole prostate was irradiated to 78 Gy were generated. The tumor control probability and rectal wall normal tissue complication probability were calculated and compared between the two IMRT approaches.

RESULTS

Combined DCE-MRI and MRSI yielded a clearly defined single DIL volume (range, 1.1-6.5 cm3) in all patients. In this small, selected patient population, no differences in tumor control probability were found. A decrease in the rectal wall normal tissue complication probability was observed in favor of the DIL-IMRT plan versus the plan with IMRT to 78 Gy.

CONCLUSION

Combined DCE-MRI and MRSI functional image-guided high-dose intraprostatic DIL-IMRT planned as a boost to 90 Gy is theoretically feasible. The preliminary results have indicated that DIL-IMRT may improve the therapeutic ratio by decreasing the normal tissue complication probability with an unchanged tumor control probability. A larger patient population, with more variations in the number, size, and localization of the DIL, and a feasible mechanism for treatment implementation has to be studied to extend these preliminary tumor control and toxicity estimates.

Prostate cancer: local staging at 3-T endorectal MR imaging--early experience

PURPOSE

To prospectively investigate the local staging accuracy of 3-T endorectal magnetic resonance (MR) imaging for prostate cancer by using whole-mount-section histopathologic analysis as the standard of reference.

MATERIALS AND METHODS

This study was approved by the institutional review board, and informed consent was obtained from all patients. In 35 consecutive patients (median age, 62.3 years) with biopsy-proved prostate cancer, 3-T endorectal MR imaging was performed. High-spatial-resolution endorectal T2-weighted fast spin-echo images of the prostate were obtained in three planes. MR images were prospectively evaluated by two experienced radiologists and a third radiologist who was less experienced with regard to local disease extent by using five established extracapsular criteria. Whole-mount-section histopathologic analysis was the standard of reference. Evaluation was performed according to octant and patient. Sensitivity, specificity, positive and negative predictive values, overall accuracy, and interobserver agreement were calculated.

RESULTS

Thirty-two patients who underwent radical prostatectomy were enrolled in this study. Accuracy, sensitivity, and specificity of local staging were 94% (30 of 32), 88% (seven of eight), and 96% (23 of 24), respectively, for both experienced radiologists, and these values were 81% (26 of 32), 50% (four of eight), and 92% (22 of 24), respectively, for the less experienced radiologist. There was substantial agreement between both experienced readers (kappa = 0.42-0.79) and moderate agreement between the less experienced reader and the experienced readers with respect to all extracapsular criteria. In regard to the three cases of minimal capsular invasion, two were detected by both experienced radiologists.

CONCLUSION

In this study, high accuracy for staging of prostate cancer at 3-T endorectal MR imaging, with moderate to substantial observer agreement, was demonstrated. In addition, minimal capsular invasion could be detected.

Magnetic resonance tracking of dendritic cells in melanoma patients for monitoring of cellular therapy

The success of cellular therapies will depend in part on accurate delivery of cells to target organs. In dendritic cell therapy, in particular, delivery and subsequent migration of cells to regional lymph nodes is essential for effective stimulation of the immune system. We show here that in vivo magnetic resonance tracking of magnetically labeled cells is feasible in humans for detecting very low numbers of dendritic cells in conjunction with detailed anatomical information. Autologous dendritic cells were labeled with a clinical superparamagnetic iron oxide formulation or (111)In-oxine and were co-injected intranodally in melanoma patients under ultrasound guidance. In contrast to scintigraphic imaging, magnetic resonance imaging (MRI) allowed assessment of the accuracy of dendritic cell delivery and of inter- and intra-nodal cell migration patterns. MRI cell tracking using iron oxides appears clinically safe and well suited to monitor cellular therapy in humans.

Prostate Cancer: Precision of Integrating Functional MR Imaging with Radiation Therapy Treatment by Using Fiducial Gold Markers

The use of intensity-modulated radiation therapy for treatment of dominant intraprostatic lesions may require integration of functional magnetic resonance (MR) imaging with treatment-planning computed tomography (CT). The purpose of this study was to compare prospectively the landmark and iterative closest point methods for registration of CT and MR images of the prostate gland after placement of fiducial markers. The study was approved by the institutional ethics review board, and informed consent was obtained. CT and MR images were registered by using fiducial gold markers that were inserted into the prostate. Two image registration methods--a commonly available landmark method and dedicated iterative closest point method--were compared. Precision was assessed for a data set of 21 patients by using five operators. Precision of the iterative closest point method (1.1 mm) was significantly better (P < .01) than that of the landmark method (2.0 mm). Furthermore, a method is described by which multimodal MR imaging data are reduced into a single interpreted volume that, after registration, can be incorporated into treatment planning.

Optimal timing for in vivo1H-MR spectroscopic imaging of the human prostate at 3T

Proton MR spectroscopic imaging ((1)H-MRSI) of the human prostate, which has an interesting clinical potential, may be improved by increasing the magnetic field strength from 1.5T to 3T. Both theoretical and practical considerations are necessary to optimize the pulse timing for spectroscopic imaging of the human prostate at 3T. For in vivo detection of the strongly coupled spin system of citrate, not only should the spectral shape of the signal be easy to identify, but the timing used should produce MR signals at reasonably short echo times (TEs). In this study the spectral shape of the methylene protons of citrate was simulated with density matrix calculations and checked with phantom measurements. Different calculated optimal spectral shapes were measured in patients with prostate cancer with a 2D spectroscopic imaging sequence. T(1) and T(2) relaxation times were calculated for citrate and choline, the two major metabolites of interest in the prostate. We conclude that the optimum timing for in vivo point-resolved spectroscopy (PRESS) imaging at 3T is an interpulse timing sequence of 90 degrees-25 ms-180 degrees- 37.5 ms-180 degrees-12.5 ms-echo. A short repetition time (TR) of 750 ms partially saturates choline signals, but increases the SNR per unit time for citrate, and accommodates a maximum number of weighted averages of an elliptically sampled k-space for accurate localization and minimal contamination of the individual spectra. This is illustrated by means of a 3D spectroscopic imaging experiment in a complete prostate in vivo.

Initial Experience of 3 Tesla Endorectal Coil Magnetic Resonance Imaging and 1H-Spectroscopic Imaging of the Prostate

RATIONALE AND OBJECTIVES

We sought to explore the feasibility of magnetic resonance imaging (MRI) of the prostate at 3T, with the knowledge of potential drawbacks of MRI at high field strengths.

MATERIAL AND METHOD

MRI, dynamic MRI, and 1H-MR spectroscopic imaging were performed in 10 patients with prostate cancer on 1.5T and 3T whole-body scanners. Comparable scan protocols were used, and additional high-resolution measurements at 3T were acquired. For both field strengths the signal-to-noise ratio was calculated and image quality was assessed.

RESULT

At 3T the signal-to-noise ratio improved. This resulted in increased spatial MRI resolution, which significantly improved anatomic detail. The increased spectral resolution improved the separation of individual resonances in MRSI. Contrast-enhanced time-concentration curves could be obtained with a doubled temporal resolution.

CONCLUSIONS

Initial results of endorectal 3T 1H-MR spectroscopic imaging in prostate cancer patients showed potential advantages: the increase in spatial, temporal, and spectral resolution at higher field strength may result in an improved accuracy in delineating and staging prostate cancer.

Fast acquisition-weighted three-dimensional proton MR spectroscopic imaging of the human prostate

The clinical application of 3D proton spectroscopic imaging (3D SI) of the human prostate requires a robust suppression of periprostatic lipid signal contamination, minimal intervoxel signal contamination, and the shortest possible measurement time. In this work, a weighted elliptical sampling of k-space, combined with k-space filtering and pulse repetition time (TR) reduction minimized lipid signals, intervoxel contamination, and measurement time. At 1.5 T, the MR-visible prostate metabolites citrate, creatine, and choline can now be mapped over the entire human prostate with uncontaminated spherical voxels, with a volume down to 0.37 cm3, in measurement times of 7-15 min.