Pitch (CT)
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Updates to Article Attributes
Pitch (P) is is a term used in helical CT. It has with two terminologies depending on whether single slice or multislice CT scanners are used 1-3.
Single slice CT (SSCT)
The term detector pitch is used and is defined as is the table distance travelled in one 360° gantry rotation divided by beam collimation 2.
For example, if the table travelled 5 mm in one rotation and the beam collimation was 5 mm, then pitch equals 5 mm / 5 mm = 1.0.
Choice of pitch affects both image quality and patient dose 2:
P = 1.0: x-ray beams are contiguous for adjacent rotations
P >1.0: x-ray beams are not contiguous for adjacent rotations;
ii.e. there are gaps in the x-ray helix, but the full volume is still irradiated, only with fewer projections per rotationP <1.0: there is x-ray beam overlap; i.e. a volume of tissue is irradiated more than once per scan
Thus, a pitch >1.0 results in decreased patient dose but also decreased image quality (fewer projections are obtained, resulting in a lower SNRsignal-to-noise ratio). A pitch of <1.0 results in better image quality, but a higher patient dose.
Multislice CT (MSCT)
Beam pitch is is defined as table distance travelled in one 360° gantry gantry rotation divided by the total thickness of all simultaneously acquired slices 3.
-<p><strong>Pitch (P)</strong> is a term used in <a href="/articles/helical-ct-image-acquisition-1">helical CT</a>. It has two terminologies depending on whether single slice or multislice CT scanners are used <sup>1-3</sup>.</p><h5>Single slice CT (SSCT)</h5><p>The term <strong>detector pitch</strong> is used and is defined as table distance travelled in one 360° gantry rotation divided by beam collimation <sup>2</sup>.</p><p>For example, if the table travelled 5 mm in one rotation and the beam collimation was 5 mm then pitch equals 5 mm / 5 mm = 1.0. </p><p>Choice of pitch affects both image quality and patient dose <sup>2</sup>:</p><ul>-<li>P = 1.0: x-ray beams are contiguous for adjacent rotations</li>-<li>P >1.0: x-ray beams are not contiguous for adjacent rotations; i.e. there are gaps in the x-ray helix, but the full volume is still irradiated, only with fewer projections per rotation</li>-<li>P <1.0: there is x-ray beam overlap; i.e. a volume of tissue is irradiated more than once per scan</li>-</ul><p>Thus a pitch >1.0 results in decreased patient dose but also decreased image quality (fewer projections are obtained, resulting in lower SNR). A pitch of <1.0 results in better image quality, but a higher patient dose. </p><h5>Multislice CT (MSCT) </h5><p><strong>Beam pitch</strong> is defined as table distance travelled in one 360° gantry rotation divided by the total thickness of all simultaneously acquired slices <sup>3</sup>.</p>- +<p><strong>Pitch (P)</strong> is a term used in <a href="/articles/helical-ct-image-acquisition-1">helical CT</a> with two terminologies depending on whether single slice or multislice CT scanners are used <sup>1-3</sup>.</p><h5>Single slice CT (SSCT)</h5><p>The term <strong>detector pitch</strong> is the table distance travelled in one 360° gantry rotation divided by beam collimation <sup>2</sup>.</p><p>For example, if the table travelled 5 mm in one rotation and the beam collimation was 5 mm, then pitch equals 5 mm / 5 mm = 1.0. </p><p>Choice of pitch affects both image quality and patient dose <sup>2</sup>:</p><ul>
- +<li><p>P = 1.0: x-ray beams are contiguous for adjacent rotations</p></li>
- +<li><p>P >1.0: x-ray beams are not contiguous for adjacent rotations; i.e. there are gaps in the x-ray helix, but the full volume is still irradiated, only with fewer projections per rotation</p></li>
- +<li><p>P <1.0: there is x-ray beam overlap; i.e. a volume of tissue is irradiated more than once per scan</p></li>
- +</ul><p>Thus, a pitch >1.0 results in decreased patient dose but also decreased image quality (fewer projections are obtained, resulting in a lower <a href="/articles/signal-to-noise-ratio-ct" title="Signal-to-noise ratio (CT)">signal-to-noise ratio</a>). A pitch of <1.0 results in better image quality but a higher patient dose. </p><h5>Multislice CT (MSCT) </h5><p><strong>Beam pitch</strong> is defined as table distance travelled in one 360° gantry rotation divided by the total thickness of all simultaneously acquired slices <sup>3</sup>.</p>
References changed:
- 1. Penelope J. Allisy-Roberts, Jerry Williams. Farr's Physics for Medical Imaging. (2007) ISBN: 9780702028441 - <a href="http://books.google.com/books?vid=ISBN9780702028441">Google Books</a>
- 2. Silverman P, Kalender W, Hazle J. Common Terminology for Single and Multislice Helical CT. AJR Am J Roentgenol. 2001;176(5):1135-6. <a href="https://doi.org/10.2214/ajr.176.5.1761135">doi:10.2214/ajr.176.5.1761135</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/11312166">Pubmed</a>
- 1. Allisy-Roberts P, Williams J. Farr's Physics for Medical Imaging. Saunders Limited. (2007) ISBN:0702028444. <a href="http://books.google.com/books?vid=ISBN0702028444">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/0702028444?ie=UTF8&tag=radiopaediaor-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=0702028444">Find it at Amazon</a><div class="ref_v2"></div>
- 2. Silverman PM, Kalender WA, Hazle JD. Common terminology for single and multislice helical CT. AJR Am J Roentgenol. 2001;176 (5): 1135-6. <a href="http://dx.doi.org/10.2214/ajr.176.5.1761135">doi:10.2214/ajr.176.5.1761135</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/11312166">Pubmed citation</a><span class="ref_v3"></span>
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