Wednesday, April 22, 2015

Multi-slice Helical CT: Physics, Image Reconstruction Principles, Scanning Techniques and Clinical Applications

The aim of this exhibit is to give the reader an introduction to the technical principles of multi-slice helical computed tomography (MSHCT) and give examples of clinical applications.

The Theory/Technical part discusses different types of detectors, table speed, pitch and image reconstruction principles. Comparisons are made with single-slice helical CT (SSHCT).

The Clinical applications exemplify isotropic imaging, multiplanar reformats (MPR), long anatomic coverage, three dimensional images (3D), retrospective reconstruction, computed tomography angiography (CTA), maximum intensity projection (MIP), coronary calcium scoring, virtual endoscopy and brain perfusion.

Major Impact Areas for Multi-Slice CT

•The multi-slice technique has added new possibilities for faster, better and safer evaluation of many different disease states such as:

  1. trauma
  2. cardiovascular disease
  3. multi-phase abdominal exams
  4. skeletal diseases
  5. pediatrics
  6. very large patients
  7. cancer  : - diagnosis • - staging
  8. critical care : - pulmonary emboli – infections

Future:

•The ongoing development of CT scanner hardware and software will lead to advances in detector configuration, scanning and reconstruction speeds, image quality and software functions.

•Multi-slice CT yields an increase in total image output compared to single-slice CT due to narrower collimation and overlapping slice reconstructions. MSHCT will paradoxically cause a reduction in data flow from the departments of Radiology because of the possibility to present images in a concentrated form. This will transform image data into information such as MPR and 3D images. The exhibit shows several examples of clinical applications where many hundred CT-images are reduced into one or a few relevant images.

Multi-slice is 8 times faster than single slice (4 slices at 2 rev/sec vs 1 slice at 1 rev/sec),  Why is faster better? :

  1. –Improved temporal resolution

Because faster scanning results in fewer motion artifacts due to voluntary and involun-tary (intestinal peristalsis, respirations, etc.) movement. Breath-holding is reduced.

2.   –Improved spatial resolution

Because thinner slices improve resolution in the z-axis, reducing partial volume artifacts, and increasing diagnostic accuracy.

3. –Increased concentration of intravascular contrast media

Because scanning is completed more quickly, contrast media is administered at a faster rate, improving conspicuity of arteries, veins, and pathologic conditions rich in blood flow (aneurysms, hypervascular tumors, active bleeding, etc.).

Separation of arterial and venous phases is improved.

4. –Decreased image noise

Because imaging is completed rapidly, x-ray tube current (mA) may be increased, decreasing image noise and improving quality, especially important when using thin slices and/or imaging large patients.

5. –Efficient x-ray tube utilization

Because imaging is completed rapidly, x-ray tube heating is diminished, decreasing or eliminating the need to wait for tube cooling between scans.

8 times more images are produced during the lifetime of a tube, decreasing cost.

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