IR/SR TrueFISP. Works-in-Progress package Version 1.2. For the SIEMENS Magnetom. Installation and User s Guide NUMARIS/4VA21B.

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1 Works-in-Progress package Version 1.2 For the Installation and User s Guide NUMARIS/4VA21B January 22, 2003 Section of Medical Physics, University Hospital Freiburg, Germany Contact: Klaus Scheffler PhD + Simone Peschl PhD, Hugstetterstr. 55, D Freiburg, Klaus.scheffler@unibas.ch

2 Table of Contents 1 Basic principles Sequence structure and timing References Software Installation Procedure Installation Restart the System Sequences and Protocols Single slice mode Multi slice mode Calculation of T1 and M0 map Tips and tricks Page 2 of 10

3 1 Basic principles The basic principle of T1 quantification with inversion prepared TrueFISP can be found in reference (1,2). After an inversion pulse acquisition is started with a TrueFISP sequence that detects the relaxing magnetization. The influence of the TrueFISP excitation pulse train on the recovering magnetization is relatively small compared to T1-weighted FLASH, as can be seen in the figure: TrueFISP 10 TrueFISP 50 FLASH reference FLASH 10 echo amplitude (a.u.) FLASH 20 TR = 3 ms for FLASH/TrueFISP NiSO 4 phantom (T 1 =260 ms) time after inversion pulse in ms Therefore, an exponential fit to the measured relaxation curve gives a reasonable estimation of the T1 relaxation time and proton density M Sequence structure and timing Imaging is performed with a conventional, ramped α-prepared 2D TrueFISP sequence. RF and echo spacing is equal to 2TE. For single slice imaging the positioning of the inversion/saturation slab and imaging slice is independent and free. For multi slice imaging the inversion/saturation slab is always parallel to the imaging slices. In this case the thickness of the inversion/saturation slab is 1.5 times the thickness if the imaging slices. Therefore a slice distance of at least 70% should be selected. Selective inversion pulses are based on an optimized adiabatic full passage pulse, and selective saturation pulses on an optimized SLR pulse (included in external file hypersec.pls). After inversion/saturation an α/2 prepared TrueFISP train starts that acquires several identical segments of Page 3 of 10

4 the k-space. After TR the next acquisition of a second segment is started. The number of different segments required to fill the k-space gives the number of repetitions that have to be acquired. The number of identical segments within one TR gives the number of images with different inversion times TI. The timing and k-space acquisition scheme is thus identical the segmented cine imaging used in cardiac applications. inversion/saturation segmented TrueFISP imaging segment TI1 TI2 TI3 TR TIn 1.2 References (1) Deimling M, Heid O. Magnetization prepared true FISP imaging. In: Proceedings of the Second Annual Meeting of the Society of Magnetic Resonance, San Francisco 1994 ;p (2) Scheffler K, Hennig J. T1 quantification with inversion recovery TrueFISP. Magnet Reson Med 2001; 45(4): Page 4 of 10

5 2 Software Installation Procedure Note: This package can only be used in combination with an IDEA licence! 2.1 Installation The IR TrueFISP installation CD contains the following files: 1. The Word document WIP-IRT1_trufi_VA21B.doc 2. A folder named protocol that contains 2.1. A file named WIP.edx 2.2. A folder named WIP.edxdir To install the WIP package please: 1. Place the CD in the drive tray. 2. Open the Exam Explorer. 3. Open a program region and a subprogram region. 4. Click on this subprogram region and select Object/Import. 5. Select the CD drive in the pop-up window, double-click on the folder protocol and select the file WIP.edx. To install the external RF pulse and image reconstruction ICE program please: 6. Place the CD in the drive tray. 7. Open the Windows NT Explorer (with control-escape). 8. Select the CD drive 9. Go to folder protocol/wip.edxdir/customerseq. 10. Copy the file hypersec.pls to C/MedCom/MriSiteData/measurement/. 11. Change to drive Q (MedCom on (Q:)) and create the directory Q/MriCustomer/IcePrograms. 12. Select the CD drive 13. Go to folder protocol/wip.edxdir/customerseq. 14. Copy the file IceProgramT1TrueFisp.dll to Q/MriCustomer/IcePrograms/. 15. Close the Windows NT Explorer and eject CD. 2.2 Restart the System In order for the changes to take effect (external RF pulse), you will need to restart System. Page 5 of 10

6 3 Sequences and Protocols 3.1 Single slice mode The positioning of the slice and the inversion/saturation slab is free and independent. The inversion/saturation slab can be accessed and modified via the UI on the Geometry/Saturation card: The selection between inversion and saturation can be done in the Contrast card: Page 6 of 10

7 The number n of images with different inversion times TI(1) TI(n) can be selected via the number of contrasts given in the Sequence/Part1 card. The corresponding inversion times depend on the segmentation of the k-space. If partial k-space is selected (7/8 or 6/8) the time interval between consecutive inversion times is not equidistant. The number of segments can be chosen in the Sequence/Part2 card: Page 7 of 10

8 The reordering of the segments into k-space can be sequential or interleaved, which can be selected in the Sequence/Special card. Interleaved reordering is recommended. 3.2 Multi slice mode In the multi slice mode the position of the inversion/saturation slabs is automatically parallel to the imaging slices. The thickness of the inversion/saturation slabs is roughly 1.5 times that of the imaging slices. Therefore the slice distance should be at least about 70%. The display of these slabs is switched off and only the position of the imaging slices is visible. As in multi slice spin echo imaging the TR corresponds to the repetition time of the inversion/saturation pulses within the same slice. Further parameters are identical to the single slice mode. Note: if you go back to single slice mode you have to reactivate the free inversion/saturation slab on the Geometry/Saturation card by clicking the + button. Page 8 of 10

9 3.3 Calculation of T1 and M0 map The number of calculated images is equal to the number of slices times the number of contrasts (different inversion times). If the check box T1 map is activated on the Sequence/Special card the reconstruction program will additionally calculate a T1 and M0 map. This feature can be used both for inversion or saturation recovery. The gray values of the T1 map corresponds to the T1 value in ms. The gray values of the M0 map is proportional to the proton density. Page 9 of 10

10 3.4 Tips and tricks The number of contrasts (i.e. different inversion/saturation times) and the time interval between successive inversion/saturation times (controlled by the number of segments) should be chosen carefully in order to provide an efficient sampling of the relaxation curve. Too long or too short inversion/saturation times will give poor T1 and M0 estimations. A short TR will decrease the M0 value. There is also some systematic error in the T1 estimation due to saturation effects of the TrueFISP sequence. The flip angle should therefore be less or equal 40. If the T1/M0 fitting routine is not able to calculate reasonable values (i.e. less than 3 inversion/saturation times, signal too small, no zero crossing of the inversion curve) T1 and M0 is set to zero. Page 10 of 10