Introduction

The clinical introduction of helical computed tomography (CT) in 1991 represented an important advance over conventional, incremental CT scanners. By producing a single volumetric data set of the thorax within one breath hold, helical CT effectively eliminated respiratory misregistration, significantly reduced respiratory and cardiac motion, decreased contrast volumes, and markedly improved the quality of multiplanar reconstruction images [1-2].

Approximately 1 decade later, multidetector helical CT (MHCT) is the latest technological breakthrough in CT scanners [3-8]. In place of a single detector array, MHCT scanners contain multiple detector arrays arranged as a matrix of multiple detector rows. Each row contains 500-900 elements, and many rows together form a curved array containing thousands of detector elements [7]. These, together with super-high-heat-capacity X-ray tubes, allow tremendous flexibility in how a scan is obtained. In comparison to single-detector CT, MHCT can be used to decrease scan time, increase spatial resolution, increase signal-to-noise ratio, or to combine all three. Moreover, MHCT

Table 1 Comparison of Existing Detector Designs

No. of

Manufacturer

elements

Type of array

Detector widths (mm)

GEa

16

Equal-width

16

X 1.25

Marconib

S

Unequal-width

2X

: 1.0., 2 X 1.5, 2 X 2.5, 2 X

5.0

Siemensc

S

Unequal-width

2X

: 1.0., 2 X 1.5, 2 X 2.5, 2 X

5.0

Toshibad

34

Unequal-width

4X

0.5, 30 X 1.0

a GE Medical Systems (Milwaukee, WI). b Marconi Medical Systems (Cleveland, OH). c Siemens Medical Systems (Iselin, NJ). d Toshiba Medical Systems (Tustin, CA).

a GE Medical Systems (Milwaukee, WI). b Marconi Medical Systems (Cleveland, OH). c Siemens Medical Systems (Iselin, NJ). d Toshiba Medical Systems (Tustin, CA).

offers the unique opportunity to create thin and thick section images from the same data set.

In this chapter, we describe the technical aspects of MHCT scanning, with a special emphasis on thoracic imaging applications. The purpose is to review the basic principles of this technique rather than to describe specific protocols for imaging. Our clinical experience with MHCT has been with the Lightspeed QXi CT scanner (General Electric, Milwaukee, WI). Although there are technical differences among MHCT scanners produced by various manufacturers (Table 1), the fundamental scanning principles are similar.

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