Magnetic resonance imaging and spectroscopic imaging of prostate cancer

Functional imaging for prostate cancer: therapeutic implications

Functional radionuclide imaging modalities, now commonly combined with anatomical imaging modalities computed tomography (CT) or magnetic resonance imaging (single photon emission computed tomography [SPECT]/CT, positron emission tomography [PET]/CT, and PET/magnetic resonance imaging), are promising tools for the management of prostate cancer, particularly for therapeutic implications. Sensitive detection capability of prostate cancer using these imaging modalities is one issue; however, the treatment of prostate cancer using the information that can be obtained from functional radionuclide imaging techniques is another challenging area. There are not many SPECT or PET radiotracers that can cover the full spectrum of the management of prostate cancer from initial detection to staging, prognosis predictor, and all the way to treatment response assessment. However, when used appropriately, the information from functional radionuclide imaging improves, and sometimes significantly changes, the whole course of the cancer management. The limitations of using SPECT and PET radiotracers with regard to therapeutic implications are not so much different from their limitations solely for the task of detecting prostate cancer; however, the specific imaging target and how this target is reliably imaged by SPECT and PET can potentially make significant impact in the treatment of prostate cancer. Finally, although the localized prostate cancer is considered manageable, there is still significant need for improvement in noninvasive imaging of metastatic prostate cancer, in treatment guidance, and in response assessment from functional imaging, including radionuclide-based techniques. In this review article, we present the rationale of using functional radionuclide imaging and the therapeutic implications for each of radionuclide imaging agent that have been studied in human subjects.

Multimodal wavelet embedding representation for data combination (MaWERiC): integrating magnetic resonance imaging and spectroscopy for prostate cancer detection

Recently, both Magnetic Resonance (MR) Imaging (MRI) and Spectroscopy (MRS) have emerged as promising tools for detection of prostate cancer (CaP). However, due to the inherent dimensionality differences in MR imaging and spectral information, quantitative integration of T(2) weighted MRI (T(2)w MRI) and MRS for improved CaP detection has been a major challenge. In this paper, we present a novel computerized decision support system called multimodal wavelet embedding representation for data combination (MaWERiC) that employs, (i) wavelet theory to extract 171 Haar wavelet features from MRS and 54 Gabor features from T(2)w MRI, (ii) dimensionality reduction to individually project wavelet features from MRS and T(2)w MRI into a common reduced Eigen vector space, and (iii), a random forest classifier for automated prostate cancer detection on a per voxel basis from combined 1.5 T in vivo MRI and MRS. A total of 36 1.5 T endorectal in vivo T(2)w MRI and MRS patient studies were evaluated per voxel by MaWERiC using a three-fold cross validation approach over 25 iterations. Ground truth for evaluation of results was obtained by an expert radiologist annotations of prostate cancer on a per voxel basis who compared each MRI section with corresponding ex vivo wholemount histology sections with the disease extent mapped out on histology. Results suggest that MaWERiC based MRS T(2)w meta-classifier (mean AUC, μ = 0.89 ± 0.02) significantly outperformed (i) a T(2)w MRI (using wavelet texture features) classifier (μ = 0.55 ± 0.02), (ii) a MRS (using metabolite ratios) classifier (μ = 0.77 ± 0.03), (iii) a decision fusion classifier obtained by combining individual T(2)w MRI and MRS classifier outputs (μ = 0.85 ± 0.03), and (iv) a data combination method involving a combination of metabolic MRS and MR signal intensity features (μ = 0.66 ± 0.02).

Correlation of phospholipid metabolites with prostate cancer pathologic grade, proliferative status and surgical stage - impact of tissue environment

This study investigates the relationship between phospholipid metabolite concentrations, Gleason score, rate of cellular proliferation and surgical stage in malignant prostatectomy samples by performing one- and two-dimensional, high-resolution magic angle spinning, total correlation spectroscopy, pathology and Ki-67 staining on the same surgical samples. At radical prostatectomy, surgical samples were obtained from 49 patients [41 with localized TNM stage T1 and T2, and eight with local cancer spread (TNM stage T3)]. Thirteen of the tissue samples were high-grade prostate cancer [Gleason score: 4 + 3 (n = 7); 4 + 4 (n = 6)], 22 low-grade prostate cancer [Gleason score: 3 + 3 (n = 17); 3 + 4 (n = 5)] and 14 benign prostate tissues. This study demonstrates that high-grade prostate cancer shows significantly higher Ki-67 staining and concentrations of phosphocholine (PC) and glycerophosphocholine (GPC) than does low-grade prostate cancer (2.4 ± 2.8% versus 7.6 ± 3.5%, p < 0.005, and 0.671 ± 0.461 versus 1.87 ± 2.15 mmolal, p < 0.005, respectively). In patients with local cancer spread, increases in [PC + GPC + PE + GPE] (PE, phosphoethanolamine; GPE, glycerophosphoethanolamine] and Ki-67 index approached significance (4.2 ± 2.5 versus 2.7 ± 2.4 mmolal, p = 0.07, and 5.3 ± 3.8% versus 2.9 ± 3.8%, p = 0.07, respectively). PC and Ki-67 were significantly lower and GPC higher in prostate tissues when compared with cell cultures, presumably because of a lack of important stromal-epithelial interactions in cell cultures. The findings of this study will need to be validated in a larger cohort of surgical patients with clinical outcome data, but support the role of in vivo (1)H MRSI in discriminating between low- and high-grade prostate cancer based on the magnitude of elevation of the in vivo total choline resonance.

In vivo tumor grading of prostate cancer using quantitative 111In-capromab pendetide SPECT/CT

We have developed an in vivo method to quantify antibody uptake using (111)In-capromab pendetide SPECT combined with CT (SPECT/CT). Our goal was to evaluate this method for potential grading of prostate tumors.

METHODS

Our phantom experiments focused on the robustness of an advanced iterative reconstruction algorithm that involves corrections for photon attenuation, scatter, and geometric blurring caused by radionuclide collimators. The conversion factors between image values and tracer concentrations (in Bq/mL) were calculated from a uniform phantom filled with an aqueous solution of (111)InCl(3) using the same acquisition protocol and reconstruction parameters as for patient studies. In addition, the spatial resolution of the reconstructed images was measured from a point source phantom. The measured spatial resolution was modeled into a point-spread function, and the point-spread function was implemented in a deconvolution-based partial-volume-error correction algorithm. The recovery capability to correctly estimate true tracer concentrations was tested using prostatelike and bladderlike lesion phantoms fitted in the modified National Electrical Manufacturers Association/International Electrotechnical Commission body phantom. Patients with biopsy-proven prostate cancer (n = 10) who underwent prostatectomy were prospectively enrolled in the preoperative SPECT/CT studies at the San Francisco Veterans Affairs Medical Center. The CT portion of SPECT/CT was used to generate CT-based attenuation maps and as an anatomic localization tool for clinical interpretation. Pathologic Gleason grades were compared with in vivo antibody uptake value (AUV) normalized by injected dose, effective half-life, and injection-scan time difference. AUVs were calculated in each lobe of the prostate gland with cylindric volumes of interest having dimensions of 1.5 cm in both diameter and height.

RESULTS

Reconstructed SPECT images further corrected by the deconvolution-based partial-volume-error correction could recover tracer concentrations up to 90% of true values in measurements of phantom volumes as small as 7.77 mL. From patient studies, there was a statistically significant correlation (rho = 0.71, P = 0.033) between higher AUVs (from either left or right lobe) and higher components of pathologic Gleason scores.

CONCLUSION

Our results strongly indicate potential for noninvasive prostate tumor grading using quantitative (111)In-capromab pendetide SPECT/CT.

Quantification of choline- and ethanolamine-containing metabolites in human prostate tissues using 1H HR-MAS total correlation spectroscopy

A fast and quantitative 2D high-resolution magic angle spinning (HR-MAS) total correlation spectroscopy (TOCSY) experiment was developed to resolve and quantify the choline- and ethanolamine-containing metabolites in human prostate tissues in approximately 1 hr prior to pathologic analysis. At a 40-ms mixing time, magnetization transfer efficiency constants were empirically determined in solution and used to calculate metabolite concentrations in tissue. Phosphocholine (PC) was observed in 11/15 (73%) cancer tissues but only 6/32 (19%) benign tissues. PC was significantly higher (0.39 +/- 0.40 mmol/kg vs. 0.02 +/- 0.07 mmol/kg, z = 3.5), while ethanolamine (Eth) was significantly lower in cancer versus benign prostate tissues (1.0 +/- 0.8 mmol/kg vs. 2.3 +/- 1.9 mmol/kg, z = 3.3). Glycerophosphocholine (GPC) (0.57 +/- 0.87 mmol/kg vs. 0.29 +/- 0.26 mmol/kg, z = 1.2), phosphoethanolamine (PE) (4.4 +/- 2.2 mmol/kg vs. 3.4 +/- 2.6 mmol/kg, z = 1.4), and glycerophosphoethanolamine (GPE) (0.54 +/- 0.82 mmol/kg vs. 0.15 +/- 0.15 mmol/kg, z = 1.8) were higher in cancer versus benign prostate tissues. The ratios of PC/GPC (3.5 +/- 4.5 vs. 0.32 +/- 1.4, z = 2.6), PC/PE (0.08 +/- 0.08 vs. 0.01 +/- 0.03, z = 3.5), PE/Eth (16 +/- 22 vs. 2.2 +/- 2.0, z = 2.4), and GPE/Eth (0.41 +/- 0.51 vs. 0.06 +/- 0.06, z = 2.6) were also significantly higher in cancer versus benign tissues. All samples were pathologically interpretable following HR-MAS analysis; however, degradation experiments showed that PC, GPC, PE, and GPE decreased 7.7 +/- 2.2%, while Cho+mI and Eth increased 18% in 1 hr at 1 degrees C and a 2250 Hz spin rate.

[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.

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.

Melanoma Metastases in Regional Lymph Nodes Are Accurately Detected by Proton Magnetic Resonance Spectroscopy of Fine-Needle Aspirate Biopsy Samples

BACKGROUND

Nonsurgical assessment of sentinel nodes (SNs) would offer advantages over surgical SN excision by reducing morbidity and costs. Proton magnetic resonance spectroscopy (MRS) of fine-needle aspirate biopsy (FNAB) specimens identifies melanoma lymph node metastases. This study was undertaken to determine the accuracy of the MRS method and thereby establish a basis for the future development of a nonsurgical technique for assessing SNs.

METHODS

FNAB samples were obtained from 118 biopsy specimens from 77 patients during SN biopsy and regional lymphadenectomy. The specimens were histologically evaluated and correlated with MRS data. Histopathologic analysis established that 56 specimens contained metastatic melanoma and that 62 specimens were benign. A linear discriminant analysis-based classifier was developed for benign tissues and metastases.

RESULTS

The presence of metastatic melanoma in lymph nodes was predicted with a sensitivity of 92.9%, a specificity of 90.3%, and an accuracy of 91.5% in a primary data set. In a second data set that used FNAB samples separate from the original tissue samples, melanoma metastases were predicted with a sensitivity of 87.5%, a specificity of 90.3%, and an accuracy of 89.1%, thus supporting the reproducibility of the method.

CONCLUSIONS

Proton MRS of FNAB samples may provide a robust and accurate diagnosis of metastatic disease in the regional lymph nodes of melanoma patients. These data indicate the potential for SN staging of melanoma without surgical biopsy and histopathological evaluation.

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.