BME358: Cardiac Magnetic Resonance Images: Normal and Heart Disease Cardiac MRI Images: Medical Imaging Assignment, SUSS, Singapore

Required Products

Cardiac magnetic resonance images: Normal and heart disease cardiac MRI images

Software: Segment – A free version of the segment.

Philips DICOM Viewer – A free version of Philips DICOM Viewer

User manual: both Segment and Philips DICOM Viewer user manual will be available to download from Canvas.

Laboratory equipment

Computer system with installed Segment and Philips DICOM Viewer.
Installation and Configuration

Installing Segment

The lab will have a copy of Segment or Philips DICOM Viewer installed on the computers. For instances where the software has not been installed, download Segment or Philips DICOM

Viewer software from http://medviso.com/products/segment/ and https://philips-dicomviewer.software.informer.com/3.0/ Follow the step-by-step instructions until the installation is complete.

Lab session: Quantification of left ventricular volume and function from CMR images using Segment or Philips DICOM Viewer

Keywords: Cardiac modeling, ventricular function, magnetic resonance imaging Synopsis: This lab session teaches the basic requirements and skills to quantify left ventricular volume and function from CMR images using Segment or Philips DICOM Viewer.

Common terminology such as magnetic resonance imaging (MRI), 4D cardiac modeling, and ventricular function is explained. Measurements of ventricular volume, ventricular mass, and ejection fraction during the cardiac cycle are performed.

Introduction

Magnetic resonance imaging (MRI) has been shown to be an accurate and precise technique to assess cardiac volumes and function in a non-invasive manner and is generally considered to be the current gold standard for cardiac imaging. Measurement of ventricular volumes, muscle mass and function is based on the determination of the left-ventricular endocardial and epicardial contours.

MRI data for an ejection fraction study is typically a multi-slice multi-phase short-axis consequence, i.e. true four-dimensional data. Temporal registration to the heart cycle is obtained by ECG-triggered MR acquisition. This ensures that frame 1 of the sequence corresponds to the maximal expansion of the ventricle, i.e. the end-diastole (ED). The temporal sampling frequency is 25 frames per cardiac cycle and the duration is one cycle. The specifications may vary dependent on hospital practice and scanner manufacturer. The data presented in this lab session is produced using a Siemens 1Tesla MR scanner. The temporal sampling frequency is 25 frames per cardiac cycle.

Segment and Philips DICOM Viewerare software that display and analyzes the medical image in DICOM format using multi-slice, and multi-frame MR images. Segment and Philips DICOM Viewer provides features for analysis of cardiac function, such as cardiac pumping and blood flow.

The resulting segmented contours may be used to calculate the following properties:

• LV mass-the mass of myocardium of the left ventricle
• LV end-diastolic volume-the volume of the blood pool when the LV is at the maximum relaxation
• LV end-systolic volume-the volume of the blood pool when the LV is at maximum contraction
• LV ejection fraction-the ratio of the end-diastolic and end-systolic volumes
• LV stroke volume-the volume of blood that is ejected from the left ventricle each cardiac cycle This information can be useful for assessing the function of the ventricle.

Origin of cardiac MRI

a) Cardiovascular Magnetic Resonance

Cardiovascular magnetic resonance (CMR) is emerging as a multipurpose imaging modality for the assessment of cardiovascular disease in general and ischemic heart disease in particular. CMR proposes to play an important clinical and investigational role in both vascular and cardiac systems.

CMR replied on exactly the same basic principles as other MR imaging techniques. During an examination, the patient is brought into a huge static magnetic field that aligns the spins of the human body. These spins can be excited and subsequently detected with coils. Their signal is influenced by two relaxation times (T1 and T2), spin density, etc. the timing of the excitation pulses and the successive magnetic field gradients determine the image contrast

General consideration

• CMR scanner with corresponding software
• Supervising physicians
• A close collaboration between radiologists and cardiologists
• Contraindications for CMR include the presence of serious claustrophobia,
  pacemaker, or internal cardiac defibrillators.

b) Imaging Protocol

The timing of a typical protocol is listed in Table 1. After obtaining scout images and a reference scan, an axial stack of black blood turbo spin-echo images is acquired to outline cardiac and noncardiac anatomy. To quantify left ventricular (LV) and right ventricular (RV) function, multiple cines are acquired in the short-axis orientation, as shown in Figure 1. In addition, long-axis images are also acquired.

In Figure 1, the top row is the two-chamber and four-chamber imaging in steady-state precession cine image of the heart. From which a stack of short-axis slices, each with equal slice thickness is positioned to cover the left and right ventricles from the atrioventricular junction to the apex (from the second row and bottom row).

Figure 1: this fugue shows cine still-frame images of a 2-chamber, a 4- chamber (top 2), and a short-axis image (second to fifth rows). A short-axis image can be obtained from the 2- and 4-chamber views, perpendicular to
the long axis of the left ventricle. Multiple short-axis cine from the apex to the base of the heart is used to quantify RV and LV function.

Objectives

Use Segment or Philips DICOM Viewer to quantify left ventricular volume and function with diverse diseases, obtain the left ventricular functional indices (end-diastolic volume, end-systolic volume, stroke volume, ejection fraction and mass index) captured from cardiac magnetic resonance images, and compare your results to the normal values (see Table 2 below)

Table 2: Normal values of left ventricular volumes, ejection fraction (EF) and myocardial mass (adopted from Introduction to cardiovascular magnetic resonance by Raad H Mohiaddin)

At the end of this practical session, you are expected to:

1. Demonstrate understanding in cardiovascular magnetic resonance (CMR) imaging acquisition and CMR scan protocol.

2. Identify the different parts of the heart from CMR images.

3. Draw contours of the endocardial and epicardial of the left ventricle.

4. Show understanding of the 3D reconstruction of magnetic resonance imaging (MRI).

5. Improve analysis of CMR images by selecting Segment or Philips DICOM Viewer to read images.

6. Obtain left ventricular functional indices (i.e. end-diastolic volume, end-systolic volume, ventricular mass, and ventricular ejection fraction).

7. Interpret the results derived from Segment or Philips DICOM Viewer (i.e. left ventricular functional indices, the motion of left ventricle during one cardiac cycle).

8. Contribute to the clinical application of medical imaging in cardiovascular disease.

9. Organize and compose a clear project report in the prescribed format

Materials

Experimental Procedures

1. Running Segment

Figure 1: Graphical user interface. The letter (a-p) in the figure will be used as references throughout the lab session

2. Loading Images from the database

Step1: Place the CMR images database in a subfolder where the segment is installed.

Step 2: In Segment, you need to set the location of the patient database. To reconstruct the database, click the rebuild database icon in the database window, Figure 2.

3. Viewing Images using Segment

Once you have loaded the images, the following screen will appear (Figure 1). This is the main viewing window of Segment. That includes viewing options, crop image stack, zoom, adjust contrast, measure distance.

4. LV segmentation

Step 1: Start the LV analysis by selecting LB[L] model (h). A new interface is opened as shown in Figure 3.

Step 2: Select the slices covering the left ventricle using left-click to select most basal slice and right-click to select most epicardial apical slice.

Step 3: Review the slice selection in the long-axis views

Step 4: Ensure the centre is in the middle of the LV

Step 5: Start the automatic LV segmentation

Step 6: The segmentation result is presented in the main window where the volume curve can be reviewed (k) and the measured LV volumes are presented, according to Figure 4.

Step 7: If needed, correction of the LV segmentation can be performed by using the following tools as shown in Figure 4.

5. Report generation

Step 1: After completing the measurements, click on the Reporter to show the report generator.

Step 2: Click on Generate HTML report, to generate an HTML report.

From a group of short and long-axis images to be used, select a set of short-axis image series and 1 long-axis image series into the left ventricle model.