Image Fusion System Fast, Reliable Guide for Tumor Treatment

Combining ultrasound with CT and MR imaging in real time is accurate and reliable for the percutaneous ablation of hepatic, renal and adrenal malignancies, according to a new study.

Luigi Solbiati, M.D. General Hospital of Busto Arsizio

"The idea was to put together the advantages of two modalities," said Luigi Solbiati, M.D., chair of the Department of Radiology at General Hospital of Busto Arsizio in Italy. Dr. Solbiati presented "Planning, Control, and Assessment of Percutaneous Ablations with Real-Time Image Fusion" at RSNA 2007. "This method delivers the speed, real-time control and low cost of ultrasound imaging, as well as the high spatial resolution of MDCT or MR."

Dr. Solbiati demonstrated the "Virtual Navigator" image fusion system, consisting of an ultrasound scanner with dedicated built-in hardware and software. A connection between the scanner and navigation software enables information on the ultrasound, regarding image size, to be exchanged. An electromagnetic tracking system integrated into the workstation consists of a magnetic field transmitter placed near the patient and a small electromagnetic wave receiver applied to the ultrasound probe. The position and orientation of the ultrasound probe is determined relative to the transmitter in order to generate the corresponding CT image. In the ultrasound room, CT scans are transferred to the navigation system in DICOM format using a LAN connection or CD.

"The system can easily, quickly and accurately guide percutaneous ablation of malignancies, including difficult-to-access and moving targets," Dr. Solbiati said. "In addition, it provides accurate and reliable intraprocedural treatment planning for the ablation of large tumors requiring multiple, precisely spaced electrode insertions to achieve complete local control."

The study included 225 patients with 426 lesions. In 181 of the patients, 260 malignancies were considered "difficult," with the remainder easily visible on ultrasound and categorized as controls.

Of the difficult malignancies, 231 were renal, hepatic or adrenal tumors ranging from 6 mm to 22 mm in size that were detected by contrast-enhanced multidetector CT (MDCT) or MR, but were poorly visible or undetectable on sonography. Another 29 were solitary large liver malignancies ranging in size from 31 mm to 63 mm and requiring multiple electrode insertions. Patients underwent percutaneous radiofrequency ablation of lesions with cool-tip electrodes. Electrode insertion within the target lesion was monitored in real time with the fusion system. The system operator used only internal anatomical landmarks to match MDCT or MR with ultrasound imaging.

The image fusion method delivers the speed, real-time control and low cost of ultrasound imaging, as well as the high spatial resolution of MDCT or MR, said presenter Luigi Solbiati, M.D.

For the 29 large malignancies, treatment planning included lesion contouring, tumor volume calculation and generation of expected necrosis volumes inside the target mass. Precision of lesion targeting and thoroughness of treatment were assessed with contrast-enhanced MDCT or MR at 24 hours and again at three months after ablation.

Researchers found that the collimation error range registered between CT or MR and ultrasound was 3.5 mm to 9.1 mm. In the 231 small malignancies, 96.1 percent of lesions were correctly targeted, with complete ablation successful in 93.1 percent of tumors.

In the 29 large liver malignancies, two to six electrode insertions were needed for each tumor and complete ablation was achieved in 96.5 percent of lesions. In seven out of the 29 cases, the 24-hour follow-up MDCT showed that the volume of necrosis was slightly larger than the size planned with fusion imaging. No complications, major or minor, occurred in any of the cases, Dr. Solbiati said.

"What was once only done with difficult mathematical calculations for every single insertion of the electrode can now be achieved with this technique," Dr. Solbiati said.

The real-time image fusion technique was also effective in two cases of lung lesions, adjacent to the pleura and difficult to localize, said Dr. Solbiati. "We tried the fusion system and it worked," he said, adding that the system can be applied to other regions as well. "It can be used not only for renal and hepatic lesions, but also for any kind of lesion in the body that can undergo ablation treatment."

Complications Rare Following Ultrasound- and CT-Guided Liver Biopsy, Study Finds

Another RSNA 2007 presentation detailed results of a 10-year study indicating that liver biopsy under CT or ultrasound guidance has a low overall complication rate and should be considered safe.

Diane Levis, P.A.-C

"We wanted to look at our complication rate for liver biopsies by radiologists, as opposed to those biopsies done in surgery or by a hepatologist without imaging," said presenter Diane Levis, a certified physician assistant in interventional radiology at Massachusetts General Hospital (MGH).

Researchers reviewed 10 years worth of medical records at MGH to determine the nature, treatment and outcomes of complications. Of 3,559 biopsies, 1,637 were focal and 1,922 were nonfocal. Complications were categorized using the Society of Interventional Radiology criteria of minor, major and death. Minor complications indicated there was no intervention needed or only overnight admission for observation was required. Major complications required therapy, greater than a 48-hour admission or prolonged hospitalization.

"The outcome of analysis showed 13 minor complications, 17 major and two deaths," said Levis. Of patients with major complications, 12 of the 17 were eventually discharged, she said.

The other five patients had malignant biopsy results and died within 30 days, said Levis, noting those patients were severely ill and biopsy may have worsened underlying comorbidities. Two deaths were directly attributed to focal biopsy—one from gall bladder injury and the other from myocardial infarction.

"Of the 32 patients with complications, 11 of them underwent nonfocal biopsy and 21 underwent focal biopsy, showing focal biopsies to be at higher risk for complication with the most common complication being bleeding," said Levis.

The overall risk for bleeding was still very low and the procedure found to be safe, Levis said. "There is already literature stating that image-guided liver biopsy under CT or ultrasound guidance is safe, but this study proves that it is," she said.