Artikel des Tages: Paramagnetic Metal Complexes as Water Proton Relaxation Agents for NMR Imaging: Theory and Design

Der heutige Artikel des Tages ist schon im Jahre 1987 erschienen, hat aber als umfassende Übersicht über Kontrastmittel für Magnetresonanzbildgebung seine Aktualität nicht verloren.

Auf 27 Seiten gibt Randall B. Lauffer, zur Zeit der Veröffentlichung am Massachusetts General Hospital und an der Harvard Medical School in Boston tätig, einen Überblick über den damals aktuellen Stand der Forschung. Die theoretischen Grundlagen fehlen ebensowenig wie lange Tabellen mit Daten zu den untersuchten Metallverbindungen und Abschnitten über die Ausbreitung der Mittel in vivo. Eine Liste mit 157 Literaturhinweisen ist das Tüpfelchen auf dem i.

Der Artikel erschien 1987 in der Zeitschrift Chemical Reviews, Vol. 87 Nr. 5, Seiten 901-927.

Artikel des Tages: An electromagnetic reverse method of coil sensitivity mapping for parallel MRI – Theoretical framework

Es geht wieder weiter - mit einem Artikel über Algorithmen für parallele Bildgebung.

Die Autoren Jin Jin, Feng Liu, Ewald Weber, Yu Li und Stuart Crozier von der University of Queensland in Brisbane (Australien) schreiben im Abstract:

In this paper, a novel sensitivity mapping method is proposed for the image domain parallel MRI (pMRI) technique. Instead of refining raw sensitivity maps by means of conventional image processing operations such as polynomial fitting, the presented method determines coil sensitivity profiles through an iterative optimization process. During the algorithm implementation the optimization cost function is defined as the difference between the raw sensitivity profile and the desired profile. The minimization is governed by the physics of low-frequency electromagnetic and reciprocity theories. The performance of the method was theoretically investigated and compared with that of a traditional polynomial fitting, against a range of system noise levels. It was found that, the new method produces high-fidelity sensitivity profiles with noise amplitudes, measured as root mean square deviation an order of magnitude less than that of the polynomial fitting method. Using the sensitivity profiles generated by our method, SENSE (sensitivity encoding) reconstructions produce significantly less image artefacts than conventional methods. The successful implementation of this method has far-reaching implications that accurate sensitivity mapping is not only important for parallel reconstruction, but also essential for its transmission analogy, such as Transmit SENSE.

Der Artikel ist im November 2010 bei der Zeitschrift Journal of Magnetic Resonance erschienen (Volume 207, Issue 1, Seiten 59-68).

Artikel des Tages: diverses über Diffusionsgewichtete Bildgebung

Ich war in den letzten Tagen nachlässig und mir gehen die deutschen Fachbegriffe aus. ;)

Aus dem ersten Grund stelle ich heute (und in den folgenden Tagen) gleich zwei Artikel vor.

Steady-state diffusion-weighted imaging: theory, acquisition and analysis

Die Autorinnen Jennifer A. McNab und Karla L. Miller vom Centre for Functional MRI of the Brain (FMRIB) der Universität Oxford schreiben im Abstract:

Steady-state diffusion-weighted imaging (DWI) has long been recognized to offer potential benefits over conventional spin-echo methods. This family of pulse sequences is highly efficient and compatible with three-dimensional acquisitions, which could enable high-resolution, low-distortion images. However, the same properties that lead to its efficiency make steady-state imaging highly susceptible to motion and create a complicated signal with dependence on T₁, T₂ and flip angle. Recent developments in gradient hardware, motion-mitigation techniques and signal analysis offer potential solutions to these problems, reviving interest in steady-state DWI. This review offers a description of steady-state DWI signal formation and provides an overview of the current methods for steady-state DWI acquisition
and analysis.

Erschienen ist der Artikel in der Zeitschrift NMR in Biomedicine, Ausgabe 23, Seiten 781-793 (August 2010).

Diffusion-Weighted MRI for Monitoring Tumor Response to Photodynamic Therapy

Diesen Artikel haben zwei in den USA forschende Mediziner aus China verfaßt:
Hesheng Wang vom Emory Center for Systems Imaging am Department of Radiology der Emory University in Atlanta, Georgia, und Baowei Fei vom Department of Biomedical Engineering der Case Western Reserve University in Cleveland, Ohio.
Bereits im Abstract führen sie genau in die verwendeten Methoden ein und geben eine Schlußfolgerung ab:

Purpose:
To examine diffusion-weighted MRI (DW-MRI) for assessing the early tumor response to photodynamic therapy (PDT).

Materials and Methods:
Subcutaneous tumor xenografts of human prostate cancer cells (CWR22) were initiated in athymic nude mice. A second-generation photosensitizer, Pc 4, was delivered to each animal by a tail vein injection 48 h before laser illumination. A dedicated high-field (9.4 Tesla) small animal MR scanner was used to acquire diffusion-weighted MR images pre-PDT and 24 h after the treatment. DW-MRI and apparent diffusion coefficients (ADC) were analyzed for 24 treated and 5 control mice with photosensitizer only or laser light only. Tumor size, prostate specific antigen (PSA) level, and tumor histology were obtained at different time points to examine the treatment effect.

Results:
Treated mice showed significant tumor size shrinkage and decrease of PSA level within 7 days after the treatment. The average ADC of the 24 treated tumors increased 24 h after PDT (P < 0.001) comparing with pre-PDT. The average ADC was 0.511 ± 0.119 × 10⁻³ mm²/s pre-PDT and 0.754 ± 0.181 × 10−3 mm²/s 24 h after the PDT. There is no significant difference in ADC values pre-PDT and 24 h after PDT in the control tumors (P = 0.20).

Conclusion:
The change of tumor ADC values measured by DW-MRI may provide a noninvasive imaging marker for monitoring tumor response to Pc 4-PDT as early as 24 h.

Dieser Artikel ist in der Ausgabe 08/2010 des Journal of Magnetic Resonance Imaging erschienen (Volume 32, Issue 2, Seiten 409–417).