The role of bone scans in electric burns

Evaluation of skull bone viability and effect of early surgical intervention in electrical contact burns using 18 F-Sodium Fluoride PET-CT imaging

OBJECTIVE

Electrical contact burns of the scalp cause serious morbidity and mortality. Early necrotic bone debridement and flap cover are crucial for successful wound closure. 18 F Sodium Fluoride (NaF), with high bone-to-soft tissue activity ratio, is useful for bone viability assessment. This study evaluated the role of 18 F NaF PET-computed tomography (CT) in objectively defining the extent and depth of nonviable calvarial bone, to guide adequate bone debridement.

METHOD

Of 20 patients referred to our institute with electrical contact burns of the scalp during a 2-year period, 15 were enrolled in the study. Two weeks after the initial management, tracer uptake pattern was noted on 18 F NaF PET-CT of the head and exposed bone measured. Surgical bone debridement was based on scan findings, followed by wound closure. All patients underwent clinical evaluation and follow-up scan 3 months after surgery.

RESULTS

Eight patients showed a central photopenic area in the exposed bone (maximum standardized uptake value [SUVmax] of 0.76 ± 0.14 with mean maximum dimensions 4.10 ± 1.76/2.67 ± 1.54 cm). High tracer uptake (SUVmax, 9.66 ± 6.03) was seen peripheral to the exposed bone (mean maximum dimensions, 8.14 ± 3.03/4.75 ± 1.61 cm). Postoperatively, there was no significant change in tracer uptake in the central debrided region or peri-debridement bone area under the flap. Clinically all patients showed a well-healed flap.

CONCLUSION

18 F NaF PET-CT appears useful for objective evaluation of skull bone viability and planning necrotic bone debridement in patients with electrical contact burns. However, additional studies with longer patient follow-up are required to validate these results.

Evaluation of bone viability in patients after girdlestone arthroplasty: comparison of bone SPECT/CT and MRI

PURPOSE

To test the diagnostic performance of bone SPECT/CT and MRI for the evaluation of bone viability in patients after girdlestone-arthroplasty with histopathology used as gold standard.

MATERIALS AND METHODS

In this cross-sectional study, patients after girdlestone-arthroplasty were imaged with single-photon-emission-computed-tomography/computed-tomography (SPECT/CT) bone-scans using 99mTc-DPD. Additionally, 1.5 T MRI was performed with turbo-inversion-recovery-magnitude (TIRM), contrast-enhanced T1-fat sat (FS) and T1-mapping. All imaging was performed within 24 h prior to revision total-hip-arthroplasty in patients with a girdlestone-arthroplasty. In each patient, four standardized bone-tissue-biopsies (14 patients) were taken intraoperatively at the remaining acetabulum superior/inferior and trochanter major/minor. Histopathological evaluation of bone samples regarding bone viability was used as gold standard.

RESULTS

A total of 56 bone-segments were analysed and classified as vital (n = 39) or nonvital (n = 17) by histopathology. Mineral/late-phase SPECT/CT showed a high sensitivity (90%) and specificity (94%) to distinguish viable and nonviable bone tissue. TIRM (sensitivity 87%, specificity 88%) and contrast-enhanced T1-FS (sensitivity 90%, specificity 88%) also achieved a high sensitivity and specificity. T1-mapping achieved the lowest values (sensitivity 82%, specificity 82%). False positive results in SPECT/CT and MRI resulted from small bone fragments close to metal artefacts.

CONCLUSIONS

Both bone SPECT/CT and MRI allow a reliable differentiation between viable and nonviable bone tissue in patients after girdlestone arthroplasty. The findings of this study could also be relevant for the evaluation of bone viability in the context of avascular bone necrosis.

Evaluation of bone viability

Bone scintigraphy is an excellent tool to assess bone viability. The functional information provided is crucial in several clinical settings, like the detection of avascular necrosis, septic embolism, frostbite lesions and osteonecrosis, and to evaluate the results of surgical treatment in cases of avascular necrosis. Mechanisms to obtain molecular images, as well as different kind of techniques, are detailed. Comparative and multimodality imaging to focus on any clinical problem and a review of the clinical indications reflect the multidisciplinary approach with close collaboration between orthopaedists, radiologists and nuclear medicine physicians. Finally, an effort has been made to list the most important points of imaging of bone viability in children.

The bone scan

Bone imaging continues to be the second greatest-volume nuclear imaging procedure, offering the advantage of total body examination, low cost, and high sensitivity. Its power rests in the physiological uptake and pathophysiologic behavior of 99m technetium (99m-Tc) diphosphonates. The diagnostic utility, sensitivity, specificity, and predictive value of 99m-Tc bone imaging for benign conditions and tumors was established when only planar imaging was available. Currently, nearly all bone scans are performed as a planar study (whole-body, 3-phase, or regional), with the radiologist often adding single-photon emission computed tomography (SPECT) imaging. Here we review many current indications for planar bone imaging, highlighting indications in which the planar data are often diagnostically sufficient, although diagnosis may be enhanced by SPECT. (18)F sodium fluoride positron emission tomography (PET) is also re-emerging as a bone agent, and had been considered interchangeable with 99m-Tc diphosphonates in the past. In addition to SPECT, new imaging modalities, including (18)F fluorodeoxyglucose, PET/CT, CT, magnetic resonance, and SPECT/CT, have been developed and can aid in evaluating benign and malignant bone disease. Because (18)F fluorodeoxyglucose is taken up by tumor cells and Tc diphosphonates are taken up in osteoblastic activity or osteoblastic healing reaction, both modalities are complementary. CT and magnetic resonance may supplement, but do not replace, bone imaging, which often detects pathology before anatomic changes are appreciated. We also stress the importance of dose reduction by reducing the dose of 99m-Tc diphosphonates and avoiding unnecessary CT acquisitions. In addition, we describe an approach to image interpretation that emphasizes communication with referring colleagues and correlation with appropriate history to significantly improve our impact on patient care.

Tc-99m pyrophosphate imaging of poloxamer-treated electroporated skeletal muscle in an in vivo rat model

OBJECTIVE

This study investigates whether (99m)Tc pyrophosphate (PYP) imaging provides a quantitative non-invasive assessment of the extent of electroporation injury, and of the effect of poloxamer in vivo on electroporated skeletal muscle.

METHODS

High-voltage electrical shock was used to produce electroporation injury in an anesthetized rat's hind limb. In each experiment, the injured limb was treated intravenously by either poloxamer-188, dextran, or saline, and subsequently imaged with (99m)Tc PYP. The radiotracer's temporal behavior among the experimental groups was compared using curve fitting of time-activity curves from the dynamic image data.

RESULTS

The washout kinetics of (99m)Tc PYP changed in proportion to the electric current magnitude that produced electroporation. Also, (99m)Tc PYP washout from electroporated muscle differed between poloxamer-188 treatment and saline treatment. Finally, 10-kDa dextran treatment of electroporated muscle altered (99m)Tc PYP washout less than poloxamer-188 treatment.

CONCLUSIONS

Behavior of (99m)Tc PYP in electroporated muscle appears to be an indicator of the amount of electroporation injury. Compared to saline, intravenous polaxamer-188 treatment reduced the amount of (99m)Tc PYP uptake. Coupled to results showing poloxamer-188 seals ruptured cellular membranes, lessens the extent of electroporation injury and improves cell viability, (99m)Tc PYP imaging appears to be a useful in vivo monitoring tool for the extent of electroporation injury.

Evaluation of arterial obstructive leg and foot disease by three-phase bone scintigraphy

BACKGROUND

The level selected for amputation should generally be the lowest compatible with tissue viability, with a reasonable expectation of wound healing in patients with arterial obstructive leg and foot disease, but determining the amputation level of an ischemic lower limb remains controversial. The general consensus is that a decisive and final decision about the amputation level should be made intraoperatively based on the extent of hemorrhage from the incised skin and soft tissue, and the degree of viability of the stump.

OBJECTIVE

To estimate the extent of such hemorrhage, and thus suggest the level of amputation preoperatively, the author applied three-phase bone scintigraphy (TPBS) to assess the blood flow in the small arteries and capillary vessels.

METHOD

TPBS was performed in patients scheduled to undergo lower limb amputation in an attempt to determine the appropriate amputation level preoperatively, objectively, and visually. Imaging results of this examination were compared with the clinical findings in three cases of arterial obstructive foot disease.

RESULTS

The "capillary phase" depicted the perfusion of blood from the small arteries to the capillary vessels. Decreased accumulation in the capillary phase appeared as two distinctive states: one of clinically remarkable necrosis and the other of decreased blood flow in the small arteries and capillary vessels. The latter inevitably causes necrosis and infection postoperatively.

CONCLUSION

The results of this study suggest that TPBS is an extremely useful tool in the evaluation of physiological dysfunction and the likely amputation level in patients with arterial obstructive leg and foot disease.

Electric burns: high- and low-tension injuries

From January 1993 to December 1997, 179 patients with electrical injuries were admitted to our burn unit. There were 55 patients with high-tension injuries and 124 patients with low-tension injuries. A high incidence of amputation (42%) is one of the characteristic sequelae of high-tension injuries, but no patients in this group of burns died. Early and serial debridement of necrotic tissue is our treatment of preference. The patient needs extensive rehabilitation and psychiatric support.