Chicago-Volumetric three-dimensional magnetic resonance urography (MRU) is a new imaging modality that is already proving to be a valuable tool for enhancing the diagnosis of various urologic conditions in pediatric patients. In addition, with a potential for use in functional and dynamic imaging, it may ultimately take on a greater role and enable streamlining of the algorithm for diagnostic evaluation, said urologists from Children's Hospital of Los Angeles (CHLA) and the University of Southern California.
The advantage of this technology is that it offers 3-D image processing far surpassing any existing reconstruction-based techniques. The generated image is clear, features superb anatomic detail, and can be viewed almost instantaneously on a PC or laptop computer, where it can be manipulated for inspection at any angle and in any plane.
Dr. Korokowski explained that recent advances in MR technology have overcome previous drawbacks by reducing test time, increasing the level of spatial detail, and improving processing techniques. As a result, there has been an explosion in the use of diagnostic MRI. Furthermore, its lack of radiation exposure makes it particularly attractive for assessment of pediatric patients.
However, existing approaches to 3-D reconstruction of the 2-D-acquired images are still limited by loss of detail.
"Current 3-D reconstruction involves computer estimation of the spaces intervening between each acquired 2-D slice, and no matter how the reconstruction is done, there is loss of detail," Dr. Kokorowski explained during a presentation at the 2006 American College of Surgeons clinical congress.
New way to acquire data
This new software for 3-D imaging acquisition was developed for use at CHLA by Lee Schiel, an independent contractor and CEO of Early Response Imaging, San Bernandino, CA. Schiel first introduced VoluMap imaging about 7 years ago and has been collaborating over the past 3 years with Dr. DeFilippo and CHLA radiologist Hollie A. Jackson, MD, to develop the software for urologic imaging.
With it, the MR data are acquired in a completely new way using a specialized T1 weighted protocol to acquire actual cubes or "voxels" of information, rather than pixels. There is no space between the voxels, so this approach provides 3-D volumetric data.
"This imaging method uses the MR machine to its fullest potential instead of just a fraction of what it is capable of doing," Dr. DeFilippo told Urology Times.
Furthermore, since all of the information necessary is obtained through acquisition of a volume slab, the test time is much faster than for a standard MRI. Using an older MR unit, image acquisition can be completed in about 45 minutes to an hour, while on a newer machine or with this protocol and software, the test time can be as short as 2 to 5 minutes, according to Dr. Kokorowski.
The 3-D image is viewed on the monitor of a computer loaded with the post-processing viewer software that allows the clinician to "visually swim through the anatomy," said Dr. DeFilippo.
"Not only can the clinician choose the angle or plane of viewing, but using sliders, it is possible to adjust the magnification level, dissect through the tissues in a 3-D plane, as well as highlight structures of interest and remove others," he explained.
Dr. Kokorowski demonstrated its utility by presenting images from two pediatric patients. One case illustrated that it provided superb visualization of ureterocele insertion into the bladder in a child with bilateral duplex systems and hydronephrosis. Another example was from a child with a horseshoe kidney and non-functioning upper pole in whom the volumetric 3-D MRU was used in conjunction with a non-gadolinium angiogram to also improve examination of the vascular anatomy.
"The ability to complete the scan without gadolinium is also novel to this particular MR application and has the benefit of significantly reducing the scan time for the patient," noted Dr. Kokorowski.
Obstacles to greater use relate primarily to the limitations of MRI itself and include equipment cost and possibly some inferiority to CT scanning for various conditions, such as urolithiasis.
"However, these issues are quickly becoming less important, especially with software applications such as VoluMap that continue to push the envelope of MR imaging in a completely new direction," Dr. DeFilippo said.