8.2 T1 Analysis Mode

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Functionality is available in a separate module which is activated in the Pro edition for an extra fee
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8.2.1 Opening Studies for T1 Analysis

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Functionality is available in a separate module which is activated in the Pro edition for an extra fee
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To open a study for quantification of the cardiac tissue T1 relaxation time, proceed as follows:

1. Choose a study and select the MR series on the basis of which the cardiac tissue relaxation time is to be evaluated.

2. Click the Cardiac analysis  button on the toolbar. To select the desired variant of the tab placement (in the current window, in a new window, in full-screen mode), press the arrow on the right-hand side of the button. To open the cardiac analysis window in a new tab within the current window, press the button. The process may take some time.

   The Cardiac analysis tool is also available in the View section of the main menu.

3. When the cardiac analysis module is activated, the Input data for cardiac analysis dialog box pops up (Fig. 8.10). From the drop-down list, select the T1 analysis mode.

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   Figure 8.10: Input data dialog box for evaluation of the tissue relaxation time

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4. From the drop-down list, select the T1 sequence type:

   • MOLLI;

   • ShMOLLI;

   • SASHA.

5. Choose the series on the basis of which a T1 map will be built. To do this, select the series on the list and click the Set as T1 button.

6. For MOLLI and ShMOLLI sequences, you can also choose a series to be used as the signal phase. To do this, select the series on the list and click the Set as T1 signal phase button.

   You cannot choose a series to be used as the signal phase for SASHA sequence.

   To reset the series type, select the series on the list and click the Reset the series type  —  button.

7. For SASHA T1 sequence, the saturation method used is to acquire multiple images with different timespans after the saturation pulse. It provides an opportunity to build a signal recovery curve, on the basis of which T1 is evaluated. From the drop-down list, select one of the adaptation models:

   • Two-parameter model. A simplified model which is less sensitive to noise. It was developed for perfect saturation and can underestimate T1 by 10–20% when the pulse is not perfect;

   • Three-parameter model. This model provides for high accuracy regardless of the pulse imperfection. But to ensure stability, the series must contain 8-11 images.

8. In the bottom part of the Input data for cardiac analysis dialog box, there is a table showing the time values for each of the T1 series images. The values are provided in the series tags. The table shows:

   • Inversion Time (TI) for MOLLI and ShMOLLI sequences;

   • Saturation Time (TS) for SASHA sequence.

   Edit these values if required.

Click OK to enter the data or CANCEL to cancel.

If the OK button in the Input data for cardiac analysis dialog box is unavailable, in order to continue work, make sure that:

• the T1 series has been chosen;

• the sequence type has been chosen;

• the number of images in the T1 series is no less than 3 for MOLLI or SASHA sequence and equals 7 for ShMOLLI sequence.

In the Cardiac analysis tab, two windows will be opened: a T1 window with a T1 map built on the basis of the selected series and a Phase T1 window with the series used as the signal phase (see Fig. 8.11).

For MOLLI and ShMOLLI sequences, you don’t have to choose a phase to be used as the signal phase. If the series used as the signal phase is not suitable for speedup of the map construction algorithm, a warning will pop up. From that time on, the T1 map will be built without this series.

On the right-hand side of the tab, there is a T1 map editing panel (see Fig. 8.12). By default, the built T1 map is superimposed on the series. To hide the map, uncheck the Visible map box. From the CLUT drop-down list, select the CLUT for the map spectrum. In the Value range range fields, specify the minimum and the maximum timespans after the saturation pulse.

There are three ways to measure intensity on a T1 map:

• mouse over a selected point on the map. The intensity value for the point indicated by the cursor is shown in the second line, in the bottom left corner of the viewer window where the cursor is placed (For details see Section 2.27);

• measure the intensity value for a certain point on the map with the Point value  tool on the toolbar (see Section 2.19.6);

• measure the average intensity value for a selected region on the map with ROI ... tools (Rectangle , Ellipse , Polygon  ) on the toolbar (see Section 2.19.7).