Spin dephasing in a magnetic dipole field

Transverse relaxation by dephasing in an inhomogeneous field is a general mechanism in physics, for example, in semiconductor physics, muon spectroscopy, or nuclear magnetic resonance. In magnetic resonance imaging the transverse relaxation provides information on the properties of several biological tissues. Since the dipole field is the most important part of the multipole expansion of the local inhomogeneous field, dephasing in a dipole field is highly important in relaxation theory. However, there have been no analytical solutions which describe the dephasing in a magnetic dipole field. In this work we give a complete analytical solution for the dephasing in a magnetic dipole field which is valid over the whole dynamic range.

A new contrast in MR mammography by means of chemical exchange saturation transfer (CEST) imaging at 3 Tesla: preliminary results

PURPOSE

To evaluate the feasibility to detect and delineate malignant breast lesions in human patients by chemical exchange saturation transfer (CEST) as an MR imaging technique without the need for contrast agent administration.

MATERIALS AND METHODS

Six female patients referred for pre-surgical staging due to histologically confirmed breast cancer were examined with MR at 3 T. The routine breast protocol included T (2w), STIR, T (1w)-DCE and contrast-enhanced T (1w) imaging with SPAIR fat suppression. For CEST imaging, a 3D RF-spoiled gradient echo (GRE) sequence with an optimized saturation pulse train was applied. To assess the diagnostic value of the technique, CEST effects observed between frequency offsets of 1.2 to 1.8 ppm from the bulk water resonance were compared to pharmacokinetic parameter maps (k (ep)) obtained by DCE-MRI.

RESULTS

In 3 of 6 patients, regions with high CEST signal intensity correlated well with tumor areas as determined by DCE-MRI. Analysis of signal intensities from ROIs in tumor, fibroglandular, adipose, and muscle tissue revealed significantly higher CEST values in tumor tissue compared to fibroglandular tissue. The detection of lesions was equally well possible with DCE-MRI and CEST-MRI. In the three other patients, the tumor regions could not be delineated based on the CEST image due to artifacts, which were most likely caused by a high content of fat tissue within the ROIs.

CONCLUSION

The results of this initial feasibility study indicate a significant potential of CEST-MRI to discriminate cancer from fibroglandular tissue in the human breast by a CEST contrast generated by endogenous solute molecules.

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.

[Multiparametric MRI of the prostate: method for early detection of prostate cancer?]

Current approaches for the early detection of prostate cancer are controversially discussed because the disease is characterized by a high incidence rate with a relatively low morbidity rate, availability of only limited prognostic markers, and continued therapy-related morbidity. Conventional morphological MRI does not play a role in early detection since small tumor foci cannot be delineated. However, if there is clinical suspicion for prostate cancer, multiparametric MRI is currently the most accurate method for detecting and characterizing suspicious lesions in the prostate. The potential to identify the so-called "index lesion", i. e., the tumor area that is most aggressive and determines treatment, is particularly important. This information can increase the accuracy of prostate biopsy and serve as a biomarker for follow-up during active surveillance. The method may considerably contribute to the urgently required separation of clinically significant from clinically insignificant prostate cancers.

Switching on the lights for real-time multimodality tumor neuroimaging: The integrated positron-emission tomography/MR imaging system

A recent report of the feasibility of simultaneous PET/MR imaging of the healthy human brain has sparked excitement in the field of neuroimaging because of its potential influence and utility in clinical neuroscience research. The aim of this communication is to discuss the benefits and current drawbacks of the hybrid imaging system and to highlight some perspectives of the new technique for brain neoplasms.

Triggering of suicidal erythrocyte death by radiocontrast agents

BACKGROUND

According to in vitro observations, gadolinium-containing magnetic resonance (MRT) contrast agents stimulate suicidal cell death or apoptosis. Similar to nucleated cells, erythrocytes may undergo suicidal death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure at the erythrocyte surface. Eryptosis is triggered by increased cytosolic Ca2+-activity. This study explored whether gadolinium-containing MRT contrast agents stimulate eryptosis.

MATERIALS AND METHODS

Annexin V-binding reflecting PS exposure and forward scatter reflecting cell volume were determined in erythrocytes within freshly drawn blood from patients (8female symbol, 3male symbol, 29-72 years) prior to and 10 min after administration of gadoterate meglumine (0.1 mmol kg(-1) b.w. Dotarem; six patients) or gadobenate dimeglumine (0.05 mmol kg(-1) bw Multi Hance; five patients). In a separate series, eryptosis was determined prior to and following in vitro incubation of erythrocytes from 16 blood donors for 4 h with gadoterate meglumine (5 mM Dotarem) or gadobenate dimeglumine (5 mM Multi Hance). Finally, eryptosis and Fluo3 fluorescence reflecting cytosolic Ca2+ were determined in vitro following exposure to Gd3+. Data were analysed using paired t-test or anova with Tukey's test as post-test.

RESULTS

The MRT contrast agents such as gadoterate meglumine (Dotarem) and gadobenate dimeglumine (Multi Hance) significantly increased the percentage of eryptotic cells. Moreover, in vitro exposure to gadoterate meglumine (5 mM), gadobenate dimeglumine (5 mM) or Gd3+ (1.9 microM) stimulated eryptosis in vitro. The effect of Gd3+ was paralleled by increase in cytosolic Ca2+-activity.

CONCLUSIONS

MRT contrast agents may stimulate suicidal erythrocyte death or eryptosis in vitro and in vivo.