3D proton MR spectroscopic imaging of prostate cancer using a standard spine coil at 1.5�T in clinical routine: a feasibility study

Developments in proton MR spectroscopic imaging of prostate cancer

In this paper, we review the developments of 1H-MR spectroscopic imaging (MRSI) methods designed to investigate prostate cancer, covering key aspects such as specific hardware, dedicated pulse sequences for data acquisition and data processing and quantification techniques. Emphasis is given to recent advancements in MRSI methodologies, as well as future developments, which can lead to overcome difficulties associated with commonly employed MRSI approaches applied in clinical routine. This includes the replacement of standard PRESS sequences for volume selection, which we identified as inadequate for clinical applications, by sLASER sequences and implementation of 1H MRSI without water signal suppression. These may enable a new evaluation of the complementary role and significance of MRSI in prostate cancer management.

In vivo biochemical investigation of spermatogenic status: 1H-MR spectroscopy of testes with nonobstructive azoospermia

OBJECTIVES

To evaluate the biochemical milieu in testes with nonobstructive azoospermia (NOA) by using proton MR spectroscopy (1H-MRS) in detecting differences in testicular metabolites between histological stages of NOA and in assessing the possible presence of spermatozoa before microdissection testicular sperm extraction (mTESE).

METHODS

Forty-nine NOA men and fifty age-matched controls were included in this prospective study. A single-voxel point-resolved spectroscopy sequence with TR/TE (2000/25 ms) was used. NOA testes were classified using the higher Johnsen score (hJS) (group 1, hJS ≥ 8; and group 2, hJS < 8). Nonparametric statistical tests were used to assess differences in normalized metabolite concentrations, defined as ratios of the metabolite concentrations versus creatine concentration between (a) NOA and controls, (b) NOA groups, and (c) NOA with positive and negative sperm retrieval.

RESULTS

Normalized concentrations of total choline (median 0.396 vs 1.09 mmol/kg, p = 0.002), myo-inositol (median 1.985 vs 3.19 mmol/kg, p = 0.002), and total lipids and macromolecules (TLM) resonating at 0.9 ppm (median 0.962 vs 2.43 mmol/kg, p = 0.024), 1.3 ppm (median 4.88 vs 10.7 mmol/kg, p = 0.043), and 2.0 ppm (median 2.33 vs 5.96 mmol/kg, p = 0.007) were reduced in NOA testes compared with controls. Decreased concentrations of TLM 2.0 (median 3.755 vs 0.436 mmol/kg, p = 0.043) were found in group 2 compared with group 1. Increased normalized concentrations of glutamate were observed in NOA testes with failed sperm retrieval (median 0.321 vs 0.000 mmol/kg, p = 0.028).

CONCLUSIONS

1H-MRS provides metabolic information about the testis in NOA patients and assesses spermatogenic status before mTESE.

KEY POINTS

• NOA testes differed from age-matched controls, in terms of reduced normalized concentrations of tChol, mI, and lipids. • TLM 2.0 peaks were found useful in the identification of NOA testes with the presence of foci of advanced spermatogenesis up to the haploid gamete stage. • Glu proved a reliable metabolic signature of spermatogenesis in NOA population by assessing the possible presence of sperm after mTESE.

Chemical shift-encoded MRI for assessment of bone marrow adipose tissue fat composition: Pilot study in premenopausal versus postmenopausal women

OBJECT

To quantify and compare subregional proximal femur bone marrow fat composition in premenopausal and postmenopausal women using chemical shift-encoded-MRI (CSE-MRI).

MATERIALS AND METHODS

A multi gradient-echo sequence at 3 T was used to scan both hips of premenopausal (n = 9) and postmenopausal (n = 18) women. Subregional fat composition (saturation, poly-unsaturation, mono-unsaturation) was quantitatively assessed in the femoral head, femoral neck, Ward's triangle, greater trochanter, and proximal shaft in bone marrow adipose tissue and separately within red and yellow marrow adipose tissue.

RESULTS

Significant differences in fat composition in postmenopausal compared to premenopausal women, which varied depending on the subregion analyzed, were found. Within both whole and yellow marrow adipose tissue, postmenopausal women demonstrated higher saturation (+14.7% to +43.3%), lower mono- (-11.4% to -33%) and polyunsaturation (-52 to -83%) (p < 0.05). Within red marrow adipose tissue, postmenopausal women demonstrated lower fat quantity (-16% to -24%) and decreased polyunsaturation (-80 to -120%) in the femoral neck, greater trochanter, and Ward's triangle (p < 0.05).

CONCLUSION

CSE-MRI can be used to detect subregional differences in proximal femur marrow adipose tissue composition between pre- and post-menopausal women in clinically feasible scan times.

MR Spectra of Normal Adult Testes and Variations with Age: Preliminary Observations

OBJECTIVES

The aim was to determine the proton MR (1H-MR) spectra of normal adult testes and variations with age.

METHODS

Forty-one MR spectra of normal testes, including 16 testes from men aged 20-39 years (group I) and 25 testes from men aged 40-69 years (group II), were analyzed. A single-voxel point-resolved spectroscopy sequence (PRESS), with TR/TE: 2000/25 ms was used. The volume of interest was placed to include the majority of normal testicular parenchyma. Association between normalized metabolite concentrations, defined as ratios of the calculated metabolite concentrations relative to creatine concentration, and age was assessed.

RESULTS

Quantified metabolites of the spectra were choline (Cho), creatine (Cr), myo-inositol (mI), scyllo-inositol, taurine, lactate, GLx compound, glucose, lipids, and macromolecules resonating at 0.9 ppm (LM09), around 20 ppm (LM20), and at 13 ppm (LM13). Most prominent peaks were Cho, Cr, mI, and lipids. A weak negative correlation between mI and age (P = 0.015) was observed. Higher normalized concentrations of Cho (P = 0.03), mI (P = 0.08), and LM13 (P = 0.05) were found in group I than in group II.

CONCLUSIONS

1H-MR spectra of a normal adult testis showed several metabolite peaks. A decrease of levels of Cho, mI, and LM13 was observed with advancing age.

KEY POINTS

• Single-voxel PRESS MRS of a normal testis is feasible. • 1H-MR spectra of a normal testis showed several metabolite peaks. • Most prominent peaks were Cho, Cr, mI, and lipids. • A decrease of Cho, mI, and LM13 was seen with advancing age.

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.

MR Spectroscopic Imaging of Peripheral Zone in Prostate Cancer Using a 3T MRI Scanner: Endorectal versus External Phased Array Coils

Magnetic resonance spectroscopic imaging (MRSI) detects alterations in major prostate metabolites, such as citrate (Cit), creatine (Cr), and choline (Ch). We evaluated the sensitivity and accuracy of three-dimensional MRSI of prostate using an endorectal compared to an external phased array “receive” coil on a 3T MRI scanner. Eighteen patients with prostate cancer (PCa) who underwent endorectal MR imaging and proton (1H) MRSI were included in this study. Immediately after the endorectal MRSI scan, the PCa patients were scanned with the external phased array coil. The endorectal coil-detected metabolite ratio [(Ch+Cr)/Cit] was significantly higher in cancer locations (1.667 ± 0.663) compared to non-cancer locations (0.978 ± 0.420) (P < 0.001). Similarly, for the external phased array, the ratio was significantly higher in cancer locations (1.070 ± 0.525) compared to non-cancer locations (0.521 ± 0.310) (P < 0.001). The sensitivity and accuracy of cancer detection were 81% and 78% using the endorectal ‘receive’ coil, and 69% and 75%, respectively using the external phased array ‘receive’ coil.

Prostate 3T-MR spectroscopic imaging without an endorectal surface coil using the MLEV-PRESS sequence

PURPOSE

The aim of this study was to determine to what extent we could identify the metabolism product peak using 3-T proton magnetic resonance spectroscopic imaging (MRSI) of the prostate gland in healthy volunteers by combining an external array coil with Malcolm Levitt composite-pulse decoupling sequence (MLEV)-point-resolved spatially localized spectroscopy (PRESS).

MATERIALS AND METHODS

MRSI data were obtained from the entire prostate gland in six healthy volunteers. The heights of the choline, citrate peaks and the standard deviation (SD) of the noise in each voxel were calculated. When the choline and/or citrate peak in a voxel exceeded 3 SD, the peak was clearly identified.

RESULTS

The clear citrate peak rate in the peripheral zone (PZ) and the central gland (CG) were 78.8 and 70.3 %, respectively. The clear choline peak rate in the PZ and the CG were 55.4 and 44.9 %, respectively. In addition, the clear peak rates for both citrate and choline in the PZ and the CG were 51.8 and 38.6 %. Therefore, in the entire prostate gland, 75.2 % had a clear citrate peak, 51.1 % had a clear choline peak, and 46.3 % had both citrate and choline peaks.

CONCLUSION

The citrate peak was clearly detected in 75.2 % of the voxels by this technique.

MRI-guided prostate biopsy detects clinically significant cancer: analysis of a cohort of 100 patients after previous negative TRUS biopsy

PURPOSE

To investigate the positive biopsy rate of MRI-guided biopsy (MR-GB) in a routine clinical setting, identify factors predictive for positive biopsy findings and to report about the clinical significance of the diagnosed tumors.

METHODS

Patients with at least one negative trans-rectal-ultrasound-guided biopsy (TRUS-GB), persistently elevated or rising serum prostate specific antigen (PSA) and at least one lesion suspicious for PCa on diagnostic 1.5 Tesla endorectal coil MRI (eMR) were included. Biopsies were carried out using a 1.5 Tesla MRI and an 18 G biopsy gun. Clinical information and biopsy results were collected; logistic regression analysis was carried out. Definite pathology reports of patients with diagnosis of PCa and subsequent radical prostatectomy (RP) were analyzed for criteria of clinical significance.

RESULTS

One hundred patients were included, mean number of previous biopsies was 2 (range 1-9), mean PSA at time of biopsy was 11.7 ng/ml (1.0-65.0), and mean prostate volume was 46.7 ccm (range 13-183). In 52/100 (52.0%) patients, PCa was detected. Out of 52 patients, 27 patients with a positive biopsy underwent RP, 20 patients radiation therapy, and 5 patients active surveillance. In total, 80.8% of the patients revealed a clinically significant PCa. In univariate regression analysis, only serum PSA levels were predictive for a positive biopsy result. Number of preceding negative biopsies was not associated with the likelihood of a positive biopsy result.

CONCLUSIONS

MR-GB shows a high detection rate of clinically significant PCa in patients with previous negative TRUS-GB and persisting suspicion for PCa.

[MR spectroscopy of the prostate with external surface coils: clinical feasibility]

PURPOSE

To determine the clinical feasibility of MR spectroscopy (MRS) of prostate cancer using external multi-channel surface coils at 1.5T. Materials and methods. Retrospective study of 31 patients with prostate cancer who underwent MRS as part of the staging work-up prior to radical prostatectomy. The ratio of the three main metabolites ([choline + creatine]/citrate) were measured along with spectral analysis of different regions of interest (ROI) placed in areas of normal tissue and cancer using the surgical specimen as the standard of reference.

RESULTS

One hundred and eighty-three voxels were analyzed. Qualitative visual analysis identified pathological spectra in 88.5% of cancer ROI, 11.7% of normal transitional zone ROI and 1.6% of normal peripheral zone ROI. The ratios of normal prostate tissue were significantly more elevated (p<0.0001) in the transition zone (0.41 +/- 0.24) than in the peripheral zone (0.22 +/- 0.36). Tumor containing voxels had significantly higher ratios (2.84 +/- 2.74) than normal tissue containing voxels of the transition zone (p<0.0001) and peripheral zone (p<0.0001).

CONCLUSION

Prostate MRS using external surface coils appears routinely feasible at 1.5T, even though it presents some limitations.

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.

Interdisziplinäre Untersuchungen zur Verbesserung der Behandlungsqualität des Prostatakarzinoms

BACKGROUND

After sufficient oncological treatment of prostate cancer the life quality becomes most important. A multi disciplinary research network aims to optimize the diagnostics and the resulting treatment of prostate cancer.

METHODS

Main characteristics of the interdisciplinary cooperation are the interlocked individual projects. A major research field is investigation of the whole mounted prostate sections to study the peripheral nerves and the comparison of histological tumor locations with the MRI. Using serial sections of prostate specimens, three-dimensional computer-animated models are created illustrating the tumors histological and immunohistochemical distributions. For nodal staging, a new methodology is investigated to demonstrate single tumor cells in lymphatic tissue lysates. A retrospective evaluation of life quality including the functional outcome is performed by using questionnaire surveys.

RESULTS

Anatomical studies gave new insights into the exact localizations of peripheral nerves which may lead to an improvement of the surgical approach in nerve-sparing radical prostatectomy. For the preoperative planning the MRI imaging might need a different interpretation in relation to the topographic location. Studies using molecular markers and their relation and distribution patterns gave new insights regarding interpretation of histological biopsy results concerning the tumor extension. Numerical quantification of tumor cells in each lymph node demonstrated micro metastases in histological negative nodes contributing to the nodal staging. A close connection of the nerve-sparing technique was demonstrated with quality of life aspects and functional results.

CONCLUSION

An interdisciplinary approach is mandatory for translational prostate cancer research. As a result, individualized diagnostic and therapeutic approaches improve oncological results and at the same time provide the best quality of life in these patients.

Current role and future perspectives of magnetic resonance spectroscopy in radiation oncology for prostate cancer

Prostatic neoplasms are not uniformly distributed within the prostate volume. With recent developments in three-dimensional intensity-modulated and image-guided radiation therapy, it is possible to treat different volumes within the prostate to different thresholds of doses. This approach has the potential to adapt the dose to the biologic aggressiveness of various clusters of tumor cells within the gland. The definition of tumor burden volume in prostate cancer can be facilitated by the use of magnetic resonance spectroscopy (MRS). The increasing sensitivity and specificity of MRS to the prostate is causing new interest in its potential role in the definition of target subvolumes at higher risk of failure following radical radiotherapy. Prostate MRS might also play a role as a noninvasive predictive factor for tumor response and treatment outcome. We review the use of MRS in radiation therapy for prostate cancer by evaluating its accuracy in the classification of aggressive cancer regions and target definition; its current role in the radiotherapy planning process, with special interest in technical issues behind the successful inclusion of MRS in clinical use; and available early experiences as a prognostic tool.

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.

Future directions in body magnetic resonance imaging

Technologic innovations in instrumentation and contrast agents naturally lead to new clinical and research applications in body MRI. Although long-range predictions of innovation are an uncertain process, short-term trends in development are more readily discernable. This review will provide examples of recent developments in magnetic resonance spectroscopic imaging, contrast agent development and molecular imaging, instrumentation, post-processing, and screening in an attempt to describe areas of active research.