Simple idea solves fusion imaging dilemma

An inexpensive vacuum cushion can help fuse whole-body PET and CT images acquired separately. While the technique needs to be tested head-to-head with hybrid PET/CT scanners, researchers are encouraged by early results, according to a study published in the June issue of the American Journal of Roentgenology.

The installed base of hybrid scanners continues to grow, but not every healthcare institution can afford one. Many hospitals still manually fuse images from dedicated PET and CT scanners. Several head/neck imaging tests have been tried successfully, but the accurate registration of whole-body images using this technique remains challenging.

Principal investigator Dr. Yuji Nakamoto and colleagues at the Institute of Biomedical Research and Innovation in Kobe, Japan, devised and tested an unpretentious scheme to coregister whole-body images obtained separately from PET and CT scanners.

They enrolled 44 patients with known or suspected cancers who underwent whole-body F-18 FDG-PET and contrast-enhanced CT lying on a polysterene-filled vacuum cushion. This cushion molded to the patients' individual contours, reducing positioning shift from one scanner to the other. The researchers later merged each scanner's data in a digital workstation using the lower margin of the bladder as a point of reference. They found the technique provided fused images of acceptable clinical value.

The average displacements for the craniocaudal, anteroposterior, and right-left views of the liver between PET and CT were 6.6 mm, 1.9 mm, and 2.3 mm, respectively. Average deviations in the craniocaudal direction for the right and left kidneys were 4.7 mm and 4 mm, respectively. The deviations of movable and static lesions above and below the diaphragm were 11.7 mm and 10.4 mm, and 9.7 mm and 6.9 mm, respectively.

"The data we have presented are comparable to the results published for a combined PET/CT imaging device," Nakamoto said.

The technique is simple and cost-effective compared with the cost of a hybrid system. Positioning and registration requires about 12 minutes and could be applied at any institution where stand-alone CT and PET scanners are ready to use. The fusion software is commercially available, and no specific algorithm for fusion is necessary.

There are disadvantages, though. Physicians have to rely on external markers for registration in cases where organs like the bladder, used as a reference point in this experiment, have changed due to surgery or other causes. The technique's positioning requirements could be uncomfortable for some patients, and coregistration results may not be accurate enough for radiation therapy planning.

Preliminary data, however, suggest this method could be a simple and clinically acceptable way to fuse PET and CT data. Researchers call for more study comparing the vacuum cushion method and PET/CT hybrid imaging.

For more information from the Diagnostic Imaging archives:

Whole-body PET/CT proves superior for staging cancers

Fusion of MR, ultrasound improves tumor targeting

Landmarking tool fuses PET, SPECT, MR, and CT

Fusion advances