Study of Attenuation Correction Using a Cardiac Dynamic Phantom: Synchronized Time-Phase-Gated Attenuation Correction Method.

In cardiac nuclear medicine examinations, absorption in the body is the main factor in the degradation of the image quality. The Chang and external source methods were used to correct for absorption in the body. However, fundamental studies on attenuation correction for electrocardiogram (ECG)-synchronized CT imaging have not been performed. Therefore, we developed and improved an ECG-synchronized cardiac dynamic phantom and investigated the synchronized time-phase-gated attenuation correction (STPGAC) method using ECG-synchronized SPECT and CT images of the same time phase. Methods: As a basic study, SPECT was performed using synchronized time-phase-gated (STPG) SPECT and non-phase-gated (NPG) SPECT. The attenuation-corrected images were, first, CT images with the same time phase as the ECG waveform of the gated SPECT acquisition (with CT images with the ECG waveform of the CT acquisition as the reference); second, CT images with asynchronous ECG; third, CT images of the 75% region; and fourth, CT images of the 40% region. Results: In the analysis of cardiac function in the phantom experiment, left ventricle ejection fraction (heart rate, 11.5%-13.4%; myocardial wall, 49.8%-55.7%) in the CT images was compared with that in the STPGAC method (heart rate, 11.5%-13.3%; myocardial wall, 49.6%-55.5%), which was closer in value to that of the STPGAC method. In the phantom polar map segment analyses, none of the images showed variability (F (10,10) < 0.5, P = 0.05). All images were correlated (r = 0.824-1.00). Conclusion: In this study, we investigated the STPGAC method using a SPECT/CT system. The STPGAC method showed similar values of cardiac function analysis to the CT images, suggesting that the STPGAC method accurately reconstructed the distribution of blood flow in the myocardial region. However, the target area for attenuation correction of the heart region was smaller than that of the whole body, and changing the gated SPECT conditions and attenuation-corrected images did not affect myocardial blood flow analysis.

Ankylosis of nonresorbable hydroxyapatite graft material as a contributing factor in recurrent periodontitis.

Many studies have shown that alloplastic bone grafts are clinically stable and safe. Nevertheless, postoperative problems such as ankylosis and root resorption are associated with alloplastic bone grafts. This report examined two cases of ankylosis of nonresorbable hydroxyapatite (NHA) alloplastic grafts associated with recurrent periodontitis. There was no clear border between the NHA particles and dentin. The particles were irregularly shaped and had plaque on the surfaces. It is postulated that ankylosis of NHA particles and dentin is a contributing factor in recurrent periodontitis.

Clinical, radiographic, and histologic evaluation of localized ridge augmentation using a mandibular bone block.

This clinical case report presents a new technique for reconstructing the vertical and horizontal dimensions of the alveolar ridge using a mandibular bone block at sites planned for single implants. Augmentation was eased with the use of a mandibular bone block, which was shaped after placement with a round bur to passively fit the dimensions of the defect, at the recipient site. After treatment, approximately 7 mm of horizontal and 3 mm of vertical augmentation were gained. Histologic observation showed that the grafted bone was well integrated with the original bone. The volume of tissue gained was sufficient for placing an implant in an optimal position. The gain in the vertical and horizontal dimensions allowed an esthetic result with a single-tooth crown.

Short-term effects of rhBMP-2-enhanced bone augmentation beyond the skeletal envelope within a titanium cap in rabbit calvarium.

BACKGROUND: Recombinant human bone morphogenetic protein (rhBMP)-2 in a bioabsorbable collagen sponge (ACS) carrier supports significant bone formation. However, histomorphometric data on the augmentation of bone formation beyond the skeletal envelope are insufficient. Our objective was to evaluate the short-term effects of rhBMP-2 on bone augmentation beyond the skeletal envelope within a titanium cap in rabbit calvarium. METHODS: Eighteen adult male Japanese white rabbits were used. ACS soak-loaded with rhBMP-2 (100, 500, or 1,000 microg/ml) was placed at the calvarium; controls were packed with ACS alone. After 1 month, the animals were euthanized, and histologic sections were prepared. Newly generated tissue and mineralized bone areas were measured histomorphometrically and expressed as percentage ratios of the total submembranous space area. RESULTS: At all concentrations, a statistically significant difference in the relative height and amount of newly generated tissue was observed between the experimental and control sites. There was a statistically significant difference in the relative amount of mineralized bone between the experimental and control sites in the 1,000-microg/ml group, but no statistically significant differences were observed in the 100-microg/ml and 500-microg/ml groups. CONCLUSION: rhBMP-2/ACS has a short-term effect on bone augmentation beyond the skeletal envelope within a titanium cap in rabbit calvarium.

Effects of marrow penetration on bone augmentation within a titanium cap in rabbit calvarium.

BACKGROUND: Some studies have advocated marrow penetration in guided bone augmentation (GBA), whereas others have shown that bone can be generated without marrow penetration. This study examined the effect of marrow penetration and the optimal rate of penetration. METHODS: In 10 rabbits, the calvarium was exposed, and circular grooves were prepared bilaterally. Within the circular groove, the external cortical surface of the skull was perforated mechanically using a number 4 round bur (experimental site), whereas the bone surface on the other groove (control site) was left intact. The rate of penetration was standardized as 28% for the experimental site and 0% for the control site. Subsequently, two standardized titanium caps with an inner diameter of 8 mm and an inner height of 4 mm were anchored in the prepared grooves. Five rabbits each were euthanized at 1 and 3 months, and the percent area of newly generated tissue and mineralized bone in the newly generated tissue under the titanium cap was determined. RESULTS: Histomorphometric analysis showed significantly increased bone neogenesis in the experimental site at 3 months. The percent area of mineralized bone in the newly generated tissue was consistently higher in the experimental site at 3 months. CONCLUSION: In the rabbit calvarium using a titanium cap GBA model, bone augmentation was significantly greater with marrow penetration than without penetration.

Open-configuration MRI study of femoro-acetabular impingement.

Femoro-acetabular impingement has been proposed as a causative factor of primary hip osteoarthritis. However, primary osteoarthritis of the hip is infrequent in Japan and other Asian countries, even though the hips of Asians frequently sustain impingement, since the Asian lifestyle commonly requires a larger range of hip motion than the Western lifestyle. Therefore, using open-configuration MRI, we investigated whether impingement actually occurs during some traditional Japanese hip positions. The hips of 5 healthy Japanese females were examined in 5 sitting postures: 1) sitting straight; 2) bowing while sitting straight; 3) sitting cross-legged; 4) W-sitting; and 5) squatting. The impingement point was detected by multiple plane reconstructed (MPR) views along with the acetabular rim depicted circumferentially. Impingement was considered to have occurred when, on MRI, the anterior femoral head-neck junction approached the acetabular rim and the femoral head was seen to float from the bottom of the acetabulum with the acetabular rim acting as a fulcrum. Impingement was observed in all volunteers in the W-sitting position, and in 2 of 5 volunteers during squatting. These findings show that impingement occurs frequently during daily Japanese activities. Thus, depending on race, femoro-acetabular impingement might not always cause primary osteoarthritis of the hip. (c) 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1582-1588, 2007.

Three-dimensional clavicular and acromioclavicular rotations during arm abduction using vertically open MRI.

There have been several reports about the clavicular and acromioclavicular motion, but a precise motion has been unknown. The purpose of this study was to analyze the 3D kinematics of the clavicle and acromioclavicular joint during arm abduction, using 3D MR images obtained by a vertically open MRI. Seven subjects participated in this investigation, which included 14 shoulders. From a seated position, we obtained MR images of their shoulder in seven abducted positions of the arm in the coronal plane. We evaluated the 3D movements of each bone in the shoulder using the volume-based registration technique, and analyzed the clavicular positions relative to the lung and the scapular positions relative to the clavicle. During arm abduction, the clavicular motion relative to the lung showed 30.6 degrees retraction, 7.3 degrees elevation, and 33.2 degrees posterior axial rotation. During arm abduction, the scapular motion relative to the clavicle showed 15.6 degrees protraction, 21.5 degrees upward rotation, and 22.2 degrees posterior tilting. This study succeeded in describing the 3D clavicular and acromioclavicular motion including the axial rotation of the clavicle, and it revealed that both motions had large degrees of rotations.

The use of porous beta-tricalcium phosphate blocks with platelet-rich plasma as an onlay bone graft biomaterial.

BACKGROUND: An experimental study of rabbit calvaria evaluated the suitability of porous beta-tricalcium phosphate (beta-TCP) block as a biomaterial for onlay bone grafting and determined whether the addition of platelet-rich plasma (PRP) can accelerate bone formation inside the pores of the beta-TCP block. METHODS: In eight rabbits, the calvarium was exposed, and the marrow was penetrated. The beta-TCP blocks were made of Ca3(CO4)3 (porosity, 75%; diameter, 8 mm; thickness, 5 mm). For the experimental group, the blocks were treated with PRP; for the control group, the blocks were treated with venous blood only. Each block was placed in the bone, attached with a titanium screw, and covered with a cutaneous flap. The animals were sacrificed after 3 months, and the tissue ingrowth into the blocks was euthanized. RESULTS: Histologic and histomorphometric measurements demonstrated that there was no inflammatory infiltration around the blocks in either group. New bone formation inside the blocks originated from the parent bone in both groups. The mineralized bone generated tended to climb along the inner walls of the block. In addition, mineralized bone formation was noted around the titanium screw. Furthermore, there was no significant difference between the experimental and control groups in the relative amounts of newly generated tissue and mineralized bone generated in the blocks. CONCLUSION: Porous beta-TCP block is a promising biomaterial for clinical situations requiring bone augmentation; however, the addition of PRP did not induce significantly more new bone formation.

The three-dimensional motions of glenohumeral joint under semi-loaded condition during arm abduction using vertically open MRI.

BACKGROUND: Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bones. It also provides 3D coordinate values. The purpose of the present study was to visualize and quantify the 3D positions of the glenohumeral joint during isometric abduction of the arm using vertically open magnetic resonance imaging. METHODS: We examined 14 shoulders of seven healthy volunteers. Magnetic resonance images were obtained in a seated position and in seven static positions of the arm from 0 degrees to maximum abduction using vertically open magnetic resonance imaging. 3D surface models were created and 3D movements of each bone in the glenohumeral joint were calculated using a computer algorithm. We analyzed the translation and contact pattern of the glenohumeral joint. FINDINGS: In supero-inferior direction, the humeral head translated slight inferiorly from +1.9 (SD 1.0) mm at 0 degrees to +0.8 (SD 1.8) mm at the maximum abduction. In antero-posterior direction, the humeral head translated anteriorly from 0 degrees to 90 degrees (mean +2.4, SD 2.6 mm) and posteriorly from 90 degrees to 150 degrees of abduction (mean -1.4, SD 2.7 mm). Furthermore, the humeral head had a unique contact patterns with the glenoid; the contact part of the humeral head with the glenoid changed from the central part to the posterior in the midrange of abduction. INTERPRETATION: The humeral head showed a small translation in the antero-posterior direction between 90 degrees and 150 degrees of abduction. In addition, the posterior part of the humeral head contacted the glenoid in this range of abduction. These findings of motion patterns in asymptomatic subjects will be necessary when comparing the kinematics with pathologic condition such as the glenohumeral instability and rotator cuff tear.

3D kinematic analysis of the acromioclavicular joint during arm abduction using vertically open MRI.

Many researchers have evaluated the motions of the shoulder girdle, especially scapular and humeral motion. However, few reports exist that describe motions of the acromioclavicular joint. The purpose of the present study was to analyze the 3D kinematics of the acromioclavicular joint during arm abduction using 3D MR images obtained by a vertically open MRI. Fourteen shoulders of seven volunteers were examined in seven static positions from 0 degrees to the maximum abduction in a seated position. 3D surface models of the clavicle and scapula were created, and the movements of the acromioclavicular joint from 0 degrees to each position were calculated using the volume-based registration technique. From these calculations, the translations were evaluated and the rotational motions were analyzed using the concept of the screw axis. In the anteroposterior direction, the clavicle translated most posteriorly (-1.9 +/- 1.3 mm) at 90 degrees of abduction and most anteriorly (1.6 +/- 2.7 mm) at maximum abduction. In the superoinferior direction, the clavicle translated slightly superiorly (0.9 +/- 1.9 mm). When analyzing relative motion of the scapula with respect to the clavicle, the scapula generally rotated about a specific screw axis passing through the insertions of both the acromioclavicular and the coracoclavicular ligaments on the coracoid process. The average rotation was 34.9 +/- 8.4 degrees.

Effects of bioactive glass on bone augmentation within a titanium cap in rabbit parietal bone.

BACKGROUND: The condition of alveolar bone influences the success and subsequent esthetics of implant treatment. This study investigated the early effects of bioactive glass (BG) on bone augmentation within a hemispherical titanium cap in rabbit parietal bone. METHODS: Twelve adult male Japanese white rabbits were used. One titanium cap (test site) was packed with BG in a collagen gel, and the other (control site) was packed with the collagen gel alone. After 1 and 3 months, animals were euthanized, and the experimental area was examined using fluorescence and light microscopy. RESULTS: Newly generated bone was observed at 1 and 3 months of healing. Although bone was also generated without BG, newly mineralized bone was generated sooner with BG present for guided bone augmentation than without BG. At 1 and 3 months, the BG was not bioabsorbed completely, and some particles remained. CONCLUSION: New bone is generated at an early stage of bone formation using BG for bone augmentation.

Effects of different sizes of beta-tricalcium phosphate particles on bone augmentation within a titanium cap in rabbit calvarium.

This study evaluated the effects of different sizes of beta-TCP particles on bone augmentation within a titanium cap. In 20 rabbits, the calvarium was exposed and a circular groove was prepared. After marrow penetration, a standardized hemispherical titanium cap was placed in the circular grove. The cap was filled with small-sized (100-250 microm) or medium-sized (250-500 microm) beta-TCP particles for the experimental site and without beta-TCP for the control site. After one and three months of healing, the animals were euthanized and examined histologically. There was a statistically significant difference in the amount of mineralized bone generated between the experimental and control groups in the three-month specimens. Furthermore, the medium-sized particles showed significantly more mineralized bone than did the small-sized particles. Based on these findings, we suggested that beta-TCP might be effective for bone formation and that medium-sized particles are more useful than small-sized particles in bone maturation.

Effects of the enamel matrix derivative and beta-tricalcium phosphate on bone augmentation within a titanium cap in rabbit calvarium.

In vitro studies suggest that enamel matrix derivative (EMD) affects the early stages of osteogenic maturation by stimulating bone cell proliferation. In the present study, we evaluated the effects of EMD and beta-tricalcium phosphate (beta-TCP) on bone augmentation within a titanium cap in rabbit calvaria, using 14 adult male Japanese white rabbits. The calvarium was exposed, a circular groove prepared, the marrow penetrated, and a standard hemispherical titanium cap placed in the groove. The cap was filled with a mixture of beta-TCP and EMD at the experimental site, and was filled with beta-TCP alone at the control site. At 1 and 3 months after cap implantation, animals were euthanized, and histological sections prepared. The sections were stained with basic fuchsin and methylene blue, and were examined using light microscopy. At 1 month, EMD tended to increase the amount of bone, but there was no significant difference in the amount of new tissue and mineralized bone between the experimental and control sites. The present findings indicate that the present mixture of EMD and beta-TCP does not accelerate bone formation, compared with beta-TCP alone.