Published ahead of print on May 13, 2009
doi: 10.3174/ajnr.A1653
Conebeam CT of the Head and Neck, Part 1: Physical Principles
A.C. Miraclea and
S.K. Mukherjia,b,c
a Department of Radiology, University of Michigan Health System, University Hospital, Ann Arbor, Mich
b Department of Otolaryngology, University of Michigan Health System, University Hospital, Ann Arbor, Mich
c Department of Radiation Oncology, University of Michigan Health System, University Hospital, Ann Arbor, Mich
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Fig 1. Schematic of an office-based CBCT scanner dedicated for extracranial head and neck imaging applications (MiniCAT). Reprinted with permission of Xoran Technologies, Ann Arbor, Mich.
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Fig 2. Depiction of CT acquisition geometries. A, Conebeam geometry in a compact office-based system designed for the patient to sit upright. B, Conventional fan-beam geometry as it is used in MDCT scanners with the patient supine.
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Fig 3. Clinical images of 2 patients acquired with the MiniCAT dedicated head and neck CBCT scanner. A–C, Axial, sagittal, and coronal images, respectively, of a patient's normal temporal bones acquired with a temporal bone protocol (40 seconds, 600 frames, 0.3-mm pixels, 125 kVp, 50.85 mA). Voxels are isometric, allowing reconstruction with equally high fidelity in the 3 depicted planes. D–F, Coronal, axial, and sagittal images, respectively, of the paranasal sinuses of a patient with mild mucosal thickenings. These images are acquired with a sinus protocol (40 seconds, 600 frames, 0.4-mm pixels, 120 kVp, 48 mA).
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Fig 4. Emission characteristics of the MiniCAT x-ray source, manufactured by Source-Ray, Inc. (Bohemia, NY). The tube voltage range is 60–125 kVp (manufacturer's data). Reprinted with permission of Xoran Technologies, Ann Arbor, Mich.
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Fig 5. Schematic depiction of the methods for reducing and subtracting x-ray scatter from total photon fluence at the detector. Methods are depicted in a series and include source filtration, compensating filtration (bow tie filter), beam collimation, antiscatter grids, and scatter-subtraction preprocessing algorithms.
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Fig 6. MTF curves for 4 MiniCAT exposure protocols. MTF curves depict spatial frequency (line pairs per centimeter) as a function of true contrast detection. Spatial resolution is conventionally described as the spatial frequency that can be discriminated with a 10% detection of true contrast. A–D, The MiniCAT protocols: sinus 20s 600 (20 seconds, 600 frames), sinus 10s 300 (10 seconds, 300 frames), sinus 10s 150 (10 seconds, 150 frames), and temporal bone 20s 600 (20 seconds, 600 frames) respectively. Spatial resolution is 8–9 lp/cm for the sinus 20s (600) protocol and 14–16 lp/cm for the temporal bone 20s (600) protocol. Reprinted with permission of Xoran Technologies, Ann Arbor, Mich.
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