Chest: Imaging of the Bony Thorax
Volume data acquisition with MDCT provides an important tool for evaluation of the bony thorax. Whether the process relates to congenital or acquired thoracic deformities, infection, trauma or neoplastic disease multidetector CT coupled with 3D rendering provides a strong imaging tool to define the presence of disease, extent of disease and help with management decisions. The role of volume rendering and its implementation have been previously defined by Pretorius found that "including volume rendered spiral CT in routine musculoskeletal imaging protocols can change management in a significant number of cases. Specific scan protocols for musculoskeletal imaging will vary on the clinical problem as well as to whether 3D rendering is needed."
MDCT is ideal for the evaluation of the patient with thoracic trauma. A single study optimized for evaluation of the lung parenchyma, aorta and the bony skeleton is ideal in the emergency room setting. An accuracy of 99% was recently reported by Novelline et al. for the evaluation of suspected aortic injury. Similarly Killeen et al. found that single detector helical CT especially with the aid of reformatted images to be useful in the detection of diaphragmatic injury. With MDCT and a faster scan time and a true volume acquisition the 3D and/or MPR images should be substantially improved. This may help increase the accuracy in injury detection.
The detection of skeletal trauma is expedited with MDCT regardless of whether the trauma is to the shoulder, spine or chest wall. Thin collimation and close interscan spacing make it ideal for datasets for 3D rendering. 3D CT is especially valuable in the more complex cases where the fracture lines are difficult to define on plain radiographs or axial CT scans alone. These include cases of fracture dislocation of the shoulder or sternum. Depending on the volume to be scanned either the 1 mm or 2.5 mm collimators are used. In small part imaging like the wrist or ankle we routinely use the 1 mm detectors in order to get 1.25 mm thick sections. For areas like the pelvis or shoulder 3.0-mm thick sections obtained from the 2.5 mm detectors is usually satisfactory especially if the data is reconstructed at 1 mm intervals. The advantages of the 2.5 mm collimation over the 1.0 mm collimators is a lower radiation dose to the patients as well as a potential increase in scanning speed by a factor of three.
Another musculoskeletal area where we have found MDCT ideal is in cases where a large volume needs to be scanned in a single breathhold, especially when the patient is in the pediatric age group. Cases including surgical revision for failed pectus surgery (so called Jeune's Syndrome) require high quality 3D maps of the thoracic cage including definition of cartilage and bony fusion prior to reconstructive surgery. Similarly other chest wall deformities like Poland's syndrome or pectus carinatum can similarly be imaged. 3D maps of the bony thorax can also detect normal variations that may simulate disease on physical examination.
"Variations in the anterior chest wall are common, occurring in one-third of children, and should be considered normal. These asymptomatic variations should not be considered alarming when palpated at physical examination." Anterior Chest Wall: Frequency of Anatomic Variations in Children
Donnelly LF et al.
Radiology 1999; 212:837-840
"Helical CT, especially with the aid of reformatted images, is useful in the diagnosis of acute diaphragmatic rupture after blunt trauma. Helical CT can be used to detect 78% of left sided and 50% of right sided injuries." Helical CT of Diaphragmatic Rupture Caused by Blunt Trauma
Killeen KL, Mirvis SE, Shanmuganathan K
AJR 1999; 173:1611-1616
"Spiral computed tomography (CT) is a powerful modality for evaluation of the musculoskeletal system, particularly when coupled with real time, volume-rendering reconstruction techniques. Including volume rendered spiral CT in routine musculoskeletal imaging protocols can change management in a significant number of cases."
Volume-rendered Three-dimensional Spiral CT: Musculoskeletal Applications
Pretorius ES, Fishman EK
RadioGraphics 1999; 19:1143-1160