Implementation of Image Reconstruction for GE SIGNA PET/MR PET Data in the STIR Library

Software for Tomographic Image Reconstruction (STIR: http://stir.sf.net) is an open source C++ library available for reconstruction of emission tomography data. This work aims at the incorporation of the GE SIGNA PET/MR scanner in STIR and enables PET image reconstruction with data corrections. The data extracted from the scanner after an acquisition includes a list of raw data files (emission, normalisation, geometric and well counter calibration (wcc) factors), magnetic resonance attenuation correction (MRAC) images and the scanner-based reconstructions. The listmode (LM) file stores a list of 'prompt' events and the singles per crystal per second. MRAC images from the scanner are used for attenuation correction. The modifications to STIR that allow accurate histogramming of this LM data in the same sinogram organisation as the scanner are also described. This allows reconstruction of acquisition data with all data corrections using STIR, and independent of any software supplied by the manufacturer. The implementations were validated by comparing the histogrammed data, data corrections and final reconstruction using the ordered subset expectation maximisation (OSEM) algorithm with the equivalents from the GE-toolbox, supplied by the manufacturer for the scanner. There is no difference in the histogrammed counts whereas an overall relative difference of 6.7 × 10 -8 % and from 0.01% to 0.86% is seen in the normalisation and randoms correction sinograms respectively. The STIR reconstructed images have similar resolution and quantification but have some residual differences due to wcc factors, decay and deadtime corrections, as well as the offset between PET and MR gantries that will be addressed in future work. This work will enable the use of all current and future STIR algorithms, including penalized image reconstruction, motion correction and direct parametric image estimation, on data from GE SIGNA PET/MR scanners

Histological examination of osteogenetic tissue obtained one year after distraction of the mandible

Distraction osteogenesis is a technique of bone lengthening and remodelling. It has become increasingly popular after 1992 when McCarty showed first cases of hypoplastic mandibles treated in this way. Authors report the histological results of the biopsy of osteogenic tissue obtained one year after distraction of the mandible performed in a young patient suffering from bilateral congenital anchilosis of the ATM, with microgenia and II Class sec. Angle, 1st Div. malocclusion. Biopsy included the distracted area and an adjacent part of the original bone. The specimen was cut in order to obtain a three-dimentional inspection of the regenerated bone in the direction of its distraction. Main results are reported. In the upper (crestal) margin and along the buccal and lingual surface, a cortical layer has been formed. The inner portion of the newly formed bone consists of cancellous bone, with interdigitating, mostly plate-like trabeculae. The density of the cancellous bone increases from the distal and mesial ends towards the center of the distracted area, and at the same time the bone architecture becomes more irregular. This indicates, that the structure of the bone formed in the earlier period of distraction is more determined by the tensile forces and becomes more randomly oriented in the later stages of the procedures. In the perifery, the trabeculae consist of a central core of initially formed bone. This core includes strands of dence fibrous tissue that are incorporated into the newly formed bone. These strands can be traced to the junction between old and new bone, where they are anchored in a broad cement line at the junction between the two bone matrixs. Ongoing, trabecular remodeling replaces this more primitive matrix compartment by mature lamellar bone. In the middle zone, the architecture of the new bone becomes more irregular, and the tissue has not fully matured jet. This is suggested by the presence of some fibrocartilaginous islands, fully surrounded by bone. Most of the fibrocartilage is already calcified or undergoes mineralization, and will soon be substituted by bone via endochondral ossification. It has to be stressed, however, that bone union is obtained in all the sections examined. The remodelling activity too is higher in the center of the distracted area and results in a continous substitution by mature lamellar bone. All these activities are accompanied by a rich vascularization, and are also reflected by numerous osteoclastic resorption and concomitant formation sites, as indicated by numerous osteoblast, osteoid seams and freshly mineralized bone. In summary, histological examinations confirms that both the quantity, as well the quality of the bone formed in the distracted area has reached a density and degree of maturation that should allow full weight-bearing

Distraction Osteogenesis of free vascularized fibula flap in reconstructed hemimandible using intraoral distraction device

Since 1989, when Hidalgo first used the free vascularized fibula flap as a new method of mandible reconstruction, this flap has been considered the treatment of choice in the reconstruction of extensive mandibular bone defects (over 6 cm) (Foster et al.,1999) resulting from trauma, infection, or tumour resections (Ferri et al.,1997). Excellent results both functionally and aesthetically (Hidalgo,1989) are obtained thanks to the adequate length (more than 20 cm of bone available), constant geometry (Yim and Wei,1994) and proper dimensions for implant placement (Frodel et al.,1993). Other main features of this flap are: the double periosteal and medullary blood supply which allows multiple osteotomies (Bahr 1998) and correct shaping, an adequate pedicle length, and a very low donor site morbidity. Bone thickness, height and its bicortical structure seem to be ideal for long term implant prosthetic rehabilitation (De Santis et al.,1999). Fibula advantages can become less effective when we deal with complex mandibular defects, which have already undergone previous treatments. Critical soft and hard tissue conditions (scars, fibrosis, bone necrosis, etc) of the recipient site can limit fibula versatility leading to sub-optimal reconstructions. Authors report their experience with two cases of distraction osteogenesis of free vascularized fibula flap performed one year after its transfer to the mandible. The first case involved a vertical distraction osteogenesis of a fibula flap used to reconstruct a hemimandible loss due to a gunshot injury (Nocini,2000). Involving a partial dentate mandible, the reconstruction lead to a vertical bone discrepancy between the flap and the residual dentate stump. To increase fibula bone height restoring the alveolar arch with respect to the occlusal plane, vertical distraction osteogenesis of the flap was performed by means of two intraoral vertical distraction devices. Distraction protocol included: 7 days of latency, a distraction rate of 0.5mm per day, 3 months of stabilization. An 11.0 mm of bone increase was obtained after 22 days. The vertical discrepancy between the fibula and the right dentate hemimandible was completely corrected. Implant surgery was successfully performed. The second case regards a horizontal distraction osteogenesis of a fibula flap used to restore a hemimandible previously treated for a tumor resection, neck dissection, radiotherapy and secondary reconstruction with an iliac crest free graft. Unstretched irradiated tissues limited the mandibular reconstruction with the fibula flap, resulting in mandibular asymmetry. Using an intraoral device, a horizontal distraction osteogenesis of the fibula was applied with the aim of elongating the flap and the fibrous soft tissue of the cheek. After a bone lengthening of 15mm mandibular symmetry was restored. Distraction protocol was the same as previously described except that the stabilization period was 7 week. There was evidence of a slight fracture of the anterior device plate, due to poor scar tissue elasticity and the presence of a cutaneous fistula over the bony gap. The device was therefore removed after the first B-scan image showed bony fusion across the distraction area. Follow up after one year showed mandibular symmetry and a functional improvement of the tongue and of the patient's speech. It is author\u2019s opinion that distraction osteogenesis can play a relevant role in the improvement of functional and aesthetic results of severe mandibular reconstruction

Distraction osteogenesis of the mandible: evaluation of callus distraction using the B-scan ultrasonography

Success with elongating the maxillofacial bones by means of distraction osteogenesis is often achieved by following a few main principles. International experience has illustrated that bone formation inside the distracted gap is ensured by preserving the periosteum supply, by not exceeding the timing of the elongation, and ensuring the correct period of stability given by the device itself to the distracted segment. The age of the patient, the type and quality of the bone undergoing distraction, the size of the osteotomy as well as the final length of the distraction gap, are all factors that easily make the osteogenesis process unpredictable. Because of this, it is mandatory to find a repeatable, easily managed diagnostic system that can describe this dynamic process. The authors report their experience in the development of a new protocol for monitoring the distraction osteogenesis of the mandible using B-scan imaging. Comparison with traditional radiological methods was performed in 12 different cases of mandibular distraction osteogenesis and then analysing the information obtained. All patients underwent distraction osteogenesis by means of an intraoral distraction device. The distraction protocol included: a latency period from 5 to 7 days; a distraction rate of 0,5 to 1.0 mm once a day and a stabilization period of 8 to 16 weeks. The radiological protocol consisted of using X-ray imaging and B-scan imaging at the following times: start, middle and end of the stabilization phase. Both evaluations were performed on the same day. Results are reported. X-rays were useful after surgery and during the active distraction phase to confirm the location of the device, its fixation to the bone, the presence of any broken parts, as well as the position of the distracted bone segments. X-rays were not able to evaluate the initial active process of bone formation, while B-scan ultrasonography appeared as a valid alternative to overcome this limitation. B-scan imaging made it possible to obtain defined and repeatable information about bone growth inside the distraction gap from the beginning to the formation of the new cortical layer. Direction, rate and quality of the osteogenetic process were precisely monitored. This accuracy of information given by the B-scan images was confirmed by histological evaluations performed at the time of the device removal. Soft tissue complications were also easily detected for example: swelling, hematoma, soft tissue damage and inflammatory reaction. Analysis of the results confirmed that in the follow up of distraction osteogenesis, X-ray examination is necessary immediately after surgery and during the active distraction phase. On the other hand, during the stabilization period, ultrasound plays a relevant role in monitoring the distraction osteogenesis process as well as the extra components of the maxillo-mandibular complex. After this study, it is author's opinion that B-scan imaging can be considered a radiological examination to be associated with conventional radiological procedures in the follow-up of the distraction protocol