Results: CT Clinical Practice: Data acquisition protocols

1. Your new 16 slice protocols are appreciated. In your spine protocol, you use a very high pitch and .75 gantry rotation time, which can result in noisy images due to inadequate mAs. Why do you use 120 kVp instead of the more widely used 140 kVp? Also, I assume Care Dose is off for the lumbar spine to get adequate tube current? I am trying to get rid of the noise, especially on big patients. Does the scan field of view matter-large, medium, small, etc? The reconstructed FOV on our images is 12 cm. New sensation 16 user.

2. I have been asked to investigate CT arthrograms post injection done under fluoro. Info is available for all aspect of scan parameters except type and dilution (if any) of contrast. My gut feeling is that standard CT contrasts (Omnipaque, Isovue, etc.) will result in much streaking and other degrading effects. Is there a dilution factor or other media that will allow good visualization of joint spaces or is this simply not feasible to accomplish?

3. I have been asked to perform a CT shoulder arthrogram. Can you please suggest a protocol for both the amount and type of contrast administered, as well as imaging parameters? We have a single detector scanner.

4. I would like to investigate the value of MDCT (16) in imaging the cervical spine degenerative disease. Do you think that IV contrast administration could increase the efficiency of the method by demonstrating the epidural venous plexus? If yes, which do you suggest as the optimum protocol with regard to contrast quantity and delay time?

5. I am looking for the protocols for pectus index and where to measure.

References

Binkert CA, Verdun FR, Zanetti M, Pfirrmann CW, Hodler J. CT arthrography of the glenohumeral joint: CT fluoroscopy versus conventional CT and fluoroscopy-comparison of image-guidance techniques. Radiology 2003; 229: 153-158.

• Summary: In this study evaluating techniques for CT arthrography of the shoulder, CT fluoroscopy was compared to conventional CT and fluoroscopy. The CT scans were conducted on a single detector helical scanner, and single-sections were obtained using a rotation speed of 1.5 second per rotation, 3 mm collimation, 3 mm table feed, 240 mA and 140 kV. The contrast was 2 parts iopamidol 200 diluted with 1 part normal saline, to constitute 12-15 mL of diluted iodinated contrast material.

Daunt SW. Cohen JH. Miller SF. Age-related normal ranges for the Haller index in children. Pediatric Radiology. 2004; 34(4):326-30.

• Summary: This study was a retrospective review determining the Haller index from 574 chest CT scans in normal children. The Haller index involves measuring the maximum internal transverse diameter of the chest and dividing it by the minimum anteroposterior diameter at the same level. Review of the article is advised, as it includes a description and demonstration of how to perform the measurement. The results of this study showed significant age and gender related ranges, and should serve as a guide for those evaluating for pectus excavatum with CT.

Wintermark M, Mouhsine E, Theumann N, Mordasini P, van Melle G, Leyvraz PF and Schnyder P. Thoracolumbar spine fractures in patients who have sustained severe trauma: Depiction with MDCT Radiology 2003; 227: 681-689.

• Summary: In this study comparing conventional radiography to MDCT of the thoracolumbar spine, retrospective review of the images was performed in 100 consecutive patients, 26 of whom manifested 66 vertebral fractures. Conventional radiography was 33% sensitive, and MDCT 97% sensitive. The 4 slice MDCT technique included thoracic caudocranial CT with 4 x 2.5 mm collimation, and abdominal-pelvic craniocaudal CT with 4 x 2.5 mm collimation. From these datasets, the spine was reconstructed with 2.5 mm thick sections and 2 mm interval, supplemented by sagittal and coronal reformations of the thoraco-lumbar spine.