Dr. Sidney M. Fireman, Dr. Susanne E. Perschbacher
Toronto, CBCT, St. Clair, Consult, Implants


* How can the values for magnification, slice thickness and slice interval aid in Cone Beam Computed Tomography interpretation?


CBCT images are printed at a 1:1 magnification. For implant cases it is possible to place an actual fixture over the image to see how well its size suits the case. It is also possible to measure distances with a ruler.


Slice thickness refers to tomographic thickness of the individual cuts. Thin slices provide images without superimposition which characterize intraoral and panoramic images. Typically CBCT implant studies are obtained with a thickness of 1mm, but a range of 0.5-40mm is possible.


Slice interval refers to the distance between individual cuts. For example, if there are 10 cuts obtained at 2mm intervals, the series would display a 20mm wide anatomical area.


* What are some important characteristics of DICOM files?


Digital Imaging and Communications in Medicine files are used throughout the entire world for several imaging modalities  including: computed tomography, MRI, ultrasound, PET, nuclear medicine, thermography, digital intraoral & panoramic imaging & others. DICOM-compliant files and devices provide a standardized set of protocols for healthcare professionals. DICOM files contain information which cannot be altered, such as: patient name, type & location of machine, acquisition date and imaging technique. DICOM files are an integral component of state-of-the-art imaging technology.


* What are the benefits of using rar & zip files for large file transfers?


Archiving tools such as WinRar & WinZip compress files without affecting image quality after they are expanded. They also provide greater security with encryption and password protection. Such tools are typically available in several versions including Windows and Mac. Typical DICOM file transfers for CBCT studies include up to 512 files, each being 0.5MB in size. One data set for CBCT is 260MB: compressing it into a rar file results in a single 90MB file. Once the file is downloaded it is expanded back to its original state to be imported into various software applications. When not needed any longer, the files should be archived back into a rar or zip file. The computer then only has to keep track of 1 file, not 512; this helps overall computer functionality and reduces storage space on the hard drive or backup utility.


* What types of files are suitable as email attachments?


There are 2 considerations:

(1) If the attachments are rar or zip files, some security settings may prevent them from being downloaded. (2) The main consideration is size. Most email servers will allow attachments

up to 20 or 25MB which is adequate for a few images. Data sets from CBCT should be sent by FTP or similar type means.


* What is the best degree of file compression when sending images for consultation?


Whether CBCT data sets or a single periapical are sent for an opinion, less compression generally means greater resolution. Lossless compression for TIFF files is a well-known exception. The more we can see the more reliable the opinions will be.