Low-Dose CT in Pelvic Imaging: Comparing Dose and Image Quality in Relation to Clinical Value in a Phantom Study.

OBJECTIVE. The aim of this phantom study was to determine whether low-dose CT of the pelvis can be performed using a dose similar to that used in a standard radio-graphic examination and to ascertain whether CT, with its better delineation of complex structures, has greater clinical value than radiography and therefore will result in improved patient care. Special consideration was given to CT performed using the tin filtration technique. MATERIALS AND METHODS. For dose comparison, an anthropomorphic phantom with 20 thermoluminescent dosimeters, two different CT scanners, and three conventional radiography devices were used. Seven CT protocols (including tin filtration) and four different radiographic examinations were performed. Dose calculations, objective and subjective evaluations of image quality, and figure-of-merit calculations were compared among the techniques. Furthermore, the images obtained were evaluated in a clinical context. Intraclass correlation was determined for the subjective results. RESULTS. The dose values of the tested low-dose CT protocols, in particular those using the tin filtration technique, corresponded to or were only slightly higher than the dose values of conventional pelvic radiographic images obtained in three views. Low-dose CT examinations were rated sufficient for consolidation control and had an informative value that was significantly higher than that of conventional radiography. Tin filtering showed the best results for low-dose CT in terms of combining dose and clinically relevant image quality. CONCLUSION. In this phantom study, low-dose CT was superior to radiography for visualizing and evaluating the dorsal pelvic ring, with only marginally higher radiation exposure occurring when the latest-generation CT systems were used. Tin filtration can improve image quality, create further dose reductions, or provide both benefits.

Liver Iron Content Determination Using a Volumetric Breath-Hold Gradient-Echo Sequence With In-Line R2 * Calculation.

BACKGROUND: Liver iron overload is a serious condition occurring in patients requiring blood transfusions (eg, in thalassemia and different forms of anemia) or with dysfunctional iron resorption, since there is no physiological mechanism to excrete iron. Above a certain level of iron concentration, chelation therapy is indicated. To monitor therapy success, liver iron content should be assessed regularly. A noninvasive method is important for patient management. Existing MRI methods suffer from long acquisition times and cost. PURPOSE: To study the correlation of liver iron content (LIC) reference values to liver R2 * determined using a 3D breath-hold multigradient echo (GRE) MRI sequence, employing accelerated acquisition by parallel imaging and in-line R2 * calculation. STUDY TYPE: Prospective. POPULATION: In all, 117 patients (22.1 ± 14.1 years, 66 men) suspected of iron overload. SEQUENCE: GRE. FIELD STRENGTH: 1.5T. ASSESSMENT: For comparison, a regulatory-approved method with a considerably longer scan time was used, providing LIC reference values. Participants were divided into a calibration group (65 participants), analyzed independently by two observers, and a validation group (52 participants). STATISTICAL TESTS: Linear correlation parameters were evaluated for R2 * values with LIC reference values, and for LIC determined from R2 * for validation group participants with LIC reference values. Sensitivity/specificity for clinical relevant LIC thresholds were analyzed. Interobserver variability was determined by intraclass correlation coefficient (ICC). RESULTS: Interobserver agreement was excellent, with an ICC of 0.99, P < 0.001. Good correlation (R2 = 0.89) and congruence of LIC values obtained with our method to LIC reference values was found, and almost identical diagnostic accuracy. Sensitivity/specificity were 0.98/0.67 for the diagnostic relevant LIC threshold of 4.5 mg/g and 1.0/0.95 for the threshold of 7 mg/g. DATA CONCLUSION: MRI acquisition times for determination of LIC can be significantly reduced by the use of comprehensive in-line R2 * map generation without compromising diagnostic accuracy. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 2.

Dose Reduction in Dental CT: A Phantom Study With Special Focus on Tin Filter Technique.

OBJECTIVE. The purpose of this study was to determine in a phantom the dose exposure of different dental 3D sectional imaging methods (CT and cone-beam CT [CBCT]) and different CT protocols. The aim was to establish optimal protocols with the lowest possible dose and diagnostically high image quality with special consideration given to tin prefiltration. MATERIALS AND METHODS. Dose was determined with thermoluminescence detectors at 20 different measuring points on an anthropomorphic phantom. Eight different CT protocols with and without tin filtering were compared with iterative reconstruction methods and a standard CBCT protocol. Objective and subjective image evaluations and a figure-of-merit analysis of the image data were performed by radiologists and maxillofacial surgeons. RESULTS. The determined dose-length products of the nine examinations were 5.0-111.9 mGy · cm with a calculated effective whole body dose of 20.7-505.9 µSv. Cone-beam CT was in the upper midfield with an effective dose of 229.3 µSv. On the basis of dose, objective image quality, and clinical evaluation results, tin filter protocols performed best. Protocols with higher doses were significantly less useful in the figure of merit comparison but because of their detailed bony representation are particularly necessary to answer certain questions about trauma and tumors. CONCLUSION. The use of tin filtering can reduce dose in dental CT examinations, compared with standard low-dose examinations, while maintaining good image quality. The dose performance is significantly inferior even to that of a cone-beam CT examination. High-dose protocols are necessary only for certain questions.

Frequency and Diagnostic Implications of Image Artifacts by Eye-Lens Shielding in Head CT.

OBJECTIVE: The eye lens is one of the most radiosensitive organs, and medical radiation is one of the main causes of cataracts. To protect the lens during head CT examinations, protectors have been developed; however, they can lead to image artifacts, which is a major disadvantage of their use. This study retrospectively evaluates the frequency and extent of artifacts caused by these protectors related to three anatomic regions (eye, brain, and bone) and their dependence on protector positioning. MATERIALS AND METHODS: Datasets from 261 consecutive head CT examinations obtained during 3.5 months of routine clinical imaging were assessed. Diagnostic quality of the images was evaluated by objective measuring and subjective scoring on a 5-point Likert scale. Furthermore, the position of the lens protector in correlation to the eye lens and the intensity and frequency of artifacts were analyzed. RESULTS: Only 4.6% of all analyzed examinations were completely free from artifacts; 95.4% showed artifacts at least in the orbital cavity. Although the brain was affected in 27.8% of cases, in only 5.8% of cases was there a risk of misinterpretation, such as suspected intracranial bleeding. In 24.9% of cases, the lens was not properly covered by the protector. A too cranial position of the protector was identified as the main risk factor for cerebral artifacts. CONCLUSION: Eye shielding for brain CT examinations often leads to artifacts. However, in only a small percentage of cases do these artifacts affect tissue depiction in regions beyond the eye (i.e., brain or bones). Correct positioning is mandatory to minimize artifacts.

Serum ferritin is not a reliable predictor to determine iron overload in thalassemia major patients post-hematopoietic stem cell transplantation.

OBJECTIVE: Iron overload (IO) in transfusion-dependent anemia persists after hematopoietic stem cell transplantation (HSCT) and can cause long-term organ damage. In many studies, the diagnosis of IO before and after HSCT is based on serum ferritin (SF) levels rather than on assessment of liver iron concentration (LIC) by MRI or SQUID. METHOD: In a retrospective multicenter study, we analyzed the concordance for indication of iron depletion therapy and correlation between LIC and SF of 36 thalassemia patients after HSCT. LIC was determined either by MRI-R2 (FerriScan®) or SQUID. RESULTS: The concordance between LIC and SF varies over time after transplant (P = 0.011). The correlation between SF and LIC was strong in the first year (Spearman's rho 0.75; P < 0.001). In agreement, the concordance between SF and LIC concerning indication for treatment was close to 1 with an overall error rate ca. of 10%. In particular in the first year after HSCT, SF underestimates the degree of iron overload. However, in the longitudinal analysis since the second year post-HSCT onward no association was found between LIC and SF (P = 0.217). Furthermore, in the second year after HSCT, the overall error rate was 35%, whereas in the 3rd, 4th, and >4th year, it was 58%, 60%, and 25%, respectively. CONCLUSIONS: Our data suggest serum ferritin is not a reliable predictor to determine iron overload in thalassemia patients after HSCT.

Quantification of inflammatory activity in patients with Crohn's disease using diffusion weighted imaging (DWI) in MR enteroclysis and MR enterography.

Background Individual studies have demonstrated the potential of diffusion-weighted magnetic resonance imaging (DWI-MRI) for identifying inflamed bowel segments. However, these studies were conducted with rather small patient cohorts and in most cases by means of MR enterography only. Purpose To demonstrate the feasibility of detecting inflamed bowel segments in a large collective of patients with Crohn's disease using DWI in MR enteroclysis and MR enterography and to compare the results of both techniques, also considering clinical parameters by means of the Harvey-Bradshaw Index (HBI). Material and Methods Ninety-six patients underwent MRI enteroclysis and 35 patients MR enterography, both with additional DWI. The HBI as well as apparent diffusion coefficients (ADC) in areas of inflamed and normal bowel wall were determined. Thus resulting in 208 bowel segments that were visualized and subsequently statistically analyzed. Results There were no significant differences in ADC values in MR enteroclysis and MR enterography ( P = 0.383 in inflammation, P = 0.223 in normal wall). Areas of inflammation showed statistically highly significant lower ADC values than areas of normal bowel wall ( P < 0.001). An ADC threshold of 1.56 × 10-3 mm2/s can distinguish between normal and inflamed bowel segments with a sensitivity of 97.4% and a specificity of 99.2%. A highly significant correlation could be shown between ADC and HBI values ( P = 0.001). Conclusion DWI-MRI facilitates recognition of inflamed bowel segments in patients with Crohn's disease and the ADC values show an excellent correlation to the HBI. There were no significant differences in ADC values in MR enteroclysis and MR enterography. An ADC threshold of 1.56 × 10-3 mm2/s differentiates between normal and inflamed bowel wall.

Noninvasive liver iron quantification by MRI using refocused gradient-echo (bSSFP): preliminary results.

PURPOSE: To evaluate the feasibility of using a balanced steady-state free precession sequence (bSSFP) to determine liver iron content (LIC). METHOD: Thirty-five consecutive patients with liver iron overload were examined with bSSFP. Signal intensity ratios of liver parenchyma to paraspinal muscles were retrospectively correlated with LIC values obtained by FerriScan, which was used as the reference method. Combinations of bSSFP protocols were also evaluated. The best combination was utilized to calculate LIC from bSSFP data. The sensitivity and specificity for the therapeutically relevant LIC threshold of 80 µmol/g (4.5 mg/g) were determined. RESULTS: LIC values ranged from 24 to 756 µmol/g. The best SIR-to-LIC correlation of a single protocol was obtained with a 3.5-ms repetition time (TR) and 17° excitation flip angle (FA). A combination of protocols with TRs of 3.5, 5, and 6.5 ms, each at 17° FA, yielded a superior correlation. LIC values calculated using this combination resulted in a sensitivity/specificity of 0.91/0.85. CONCLUSION: bSSFP is basically suitable to determine LIC. Its advantages are high SNR efficiency and the ability to acquire the entire liver in a breath hold without acceleration techniques. KEY POINTS: · The bSSFP sequence is suited to quantify liver iron overload.. · bSSFP has a high scanning efficiency and potential for LIC screening.. · Despite susceptibility artifacts, the LIC determined from bSSFP data showed high accuracy.. CITATION FORMAT: · Wunderlich AP, Cario H, Götz M et al. Noninvasive liver iron quantification by MRI using refocused gradient-echo (bSSFP): preliminary results. Fortschr Röntgenstr 2023; 195: 804 - 808.

Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R2* Analysis: First Experience.

PURPOSE: MR transverse relaxation rate R2* has been shown to be useful for monitoring liver iron overload. A sequence enabling acquisition of the whole liver in a single breath hold is now available, thus allowing volumetric hepatic R2* distribution studies. We evaluated the feasibility of computer-assisted whole liver segmentation of 3 D multi-gradient-echo MRI data, and compared whole liver R2* determination to analyzing only a single slice. Also, segmental R2* differences were studied. MATERIALS AND METHODS: The liver of 44 patients, investigated by multi-gradient echo MRI at 1.5 T, was segmented and divided into nine segments. Segmental R2* values were examined for all patients together and with respect to two criteria: average R2* values, and reason for iron overload. Correlation of single-slice and volumetric data was tested with Spearman's rank test, segmental and group differences were evaluated by analysis of variance. RESULTS: Whole-liver R2* values correlated excellent to single slice data (p < 0.001). The lowest R2* occurred in segment 1 (S1), differences of S1 with regard to other segments were significant in five cases and highly significant in two cases. Patients with high average R2* showed significant differences between S1 and segments 2, 6, and 7. Disease-related differences with respect to S1 were significant in segments 3 to 5 and 7. CONCLUSION: Our results suggest inhomogeneous hepatic iron distribution. Low R2* in S1 may be explained by its special vascularization. KEY POINTS: · Hepatic R2* distribution is not as homogeneous as previously thought.. · Liver segments might have a functional relevance.. · Segmental and total liver R2* values coincide best in segment 8.. CITATION FORMAT: · Wunderlich AP, Cario H, Kannengießer S et al. Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R2* Analysis: First Experience. Fortschr Röntgenstr 2023; 195: 224 - 233.

Segmental quantification of hepatic lipid content based on volumetric MRI data in patients with suspected iron overload.

PURPOSE: To investigate the segmental distribution of hepatic fat fraction, determined with MRI (MR proton density fat fraction, short MR-PDFF) in patients suspected of having liver iron overload. METHODS: The liver of 44 patients examined with MRI using a 3D multi-echo gradient-echo sequence was segmented semiautomatically and subdivided into nine segments (segment 4 divided in 4a and 4b). Segmental fat content was determined on MR-PDFF maps. Whole-liver steatosis grades were compared to those found in individual segments. Segmental MR-PDFF differences were tested for statistical significance. RESULTS: The most common diseases were thalassemia, various forms of anemia, and hereditary hemochromatosis. No patients suffered from fat metabolism disease. Iron overload was present in 37/44 (84 %) patients. For the whole liver, 22 patients showed a steatosis grade of 0, 21 patients were graded S1, and one patient had a steatosis grade of 2. The grade of steatosis was underestimated in 5 of 21 patients (24 %) in segment 8 and in 8 of 21 patients (38 %) in segment 7. Highly significant segmental MR-PDFF differences were detected with p < 0.00 001, e. g., comparing segment 2 to 5. Segments 1 to 3 had the highest fat content, segments 7 and 8 had the lowest. CONCLUSION: Our results suggest that the storage of fat in the liver is inhomogeneous, so that segment-wise differing fat concentrations were found. Fat distribution in patients with suspected hepatic iron overload was similar to living liver donors. However, it showed significant differences compared with the values published for NAFLD patients, which were less pronounced in the group with high average hepatic MR-PDFF values than in the group with normal lipid content. In patients suspected of having iron overload, segment 8, which is mainly targeted for biopsy, and segment 7 may underestimate steatosis grade. KEY POINTS: · A volumetric analysis of 3D MRI data of patients with suspected hepatic iron overload yielded a markedly elevated MR proton density fat fraction (MR-PDFF) in hepatic segments 1 to 3.. · This hepatic fat distribution, observed for the whole patient cohort, is similar to healthy living liver donors.. · The subgroup of patients with a high average MR-PDFF ≥ 6.5 % shows this effect with lower segmental deviations.. · In patients without fat metabolic disorders, the steatosis grade may be underestimated when taking biopsies in segment 8 or 7..

Organ-based tube current modulation versus spectral shaping via tin prefiltration: What does bismuth breast shielding add in low-dose lung CT?

PURPOSE: Since organ-based tube current modulation (OBTCM) and tin prefiltration are limited on their own in lowering the dose of lung CT examinations, this experimental study was designed to investigate whether combinations with anterior patient shielding can increase the dose reduction potential. MATERIAL AND METHODS: Three pairs of scan protocols without/with breast shield (P1/P2: standard 120kVp, P3/P4: OBTCM at 100 kVp, P5/P6: Sn 100 kVp) were employed for radiation exposure and image quality comparisons on an anthropomorphic Alderson-Rando phantom. Equivalent doses were measured in eleven sites via thermoluminescent dosimetry and the effective dose was obtained by summation of the weighted organ doses. Dose-weighted contrast-to-noise ratios (CNRD) were calculated and four radiologists independently assessed the quality of images generated with each protocol. RESULTS: While no significant difference was determined between standard and OBTCM protocols regardless of breast shield (p ≥ 0.068), equivalent doses with spectral shaping were substantially lower (p ≤ 0.003). The highest effective dose was ascertained for standard scans (P1/P2: 7.3/6.8 mSv) with a dose reduction of 8.0 % via breast shielding. The use of a bismuth shield was more beneficial in OBTCM (P3/P4: 6.6/5.3 mSv) and spectral shaping (P5/P6: 0.7/0.6 mSv), reducing the effective dose by 19.8 % and 13.9 %, respectively. Subjective assessment favoured standard protocol P1 over tin prefiltration low-dose scans (p ≤ 0.032), however, no scan protocol entailed diagnostically insufficient image quality. CONCLUSIONS: Whereas breast shielding is particularly beneficial in combination with OBTCM, spectral shaping via tin prefiltration facilitates the most pronounced dose reduction in lung CT imaging with acceptable image quality.

Substantial and reversible brain gray matter reduction but no acute brain lesions in ultramarathon runners: experience from the TransEurope-FootRace Project.

BACKGROUND: During the extremely challenging 4,487 km ultramarathon TransEurope-FootRace 2009, runners showed considerable reduction of body weight. The effects of this endurance run on brain volume changes but also possible formation of brain edema or new lesions were explored by repeated magnetic resonance imaging (MRI) studies. METHODS: A total of 15 runners signed an informed consent to participate in this study of planned brain scans before, twice during, and about 8 months after the race. Because of dropouts, global gray matter volume analysis could only be performed in ten runners covering three timepoints, and in seven runners who also had a follow-up scan. Scanning was performed on three identical 1.5 T Siemens MAGNETOM Avanto scanners, two of them located at our university. The third MRI scanner with identical sequence parameters was a mobile MRI unit escorting the runners. Volumetric 3D datasets were acquired using a magnetization prepared rapid acquisition gradient echo (MPRAGE) sequence. Additionally, diffusion-weighted (DWI) and fluid attenuated inversion recovery (FLAIR) imaging was performed. RESULTS: Average global gray matter volume as well as body weight significantly decreased by 6% during the race. After 8 months, gray matter volume returned to baseline as well as body weight. No new brain lesions were detected by DWI or FLAIR imaging. CONCLUSIONS: Physiological brain volume reduction during aging is less than 0.2% per year. Therefore a volume reduction of about 6% during the 2 months of extreme running appears to be substantial. The reconstitution in global volume measures after 8 months shows the process to be reversible. As possible mechanisms we discuss loss of protein, hypercortisolism and hyponatremia to account for both substantiality and reversibility of gray matter volume reductions. Reversible brain volume reduction during an ultramarathon suggests that extreme running might serve as a model to investigate possible mechanisms of transient brain volume changes. However, despite massive metabolic load, we found no new lesions in trained athletes participating in a multistage ultramarathon.See related commentary http://www.biomedcentral.com/1741-7015/10/171.

Relaxation-weighted 23Na magnetic resonance imaging maps regional patterns of abnormal sodium concentrations in amyotrophic lateral sclerosis.

Objectives: Multiparametric magnetic resonance imaging (MRI) is established as a technical instrument for the characterisation of patients with amyotrophic lateral sclerosis (ALS). The contribution of relaxation-weighted sodium (23NaR) MRI remains to be defined. The aim of this study is to apply 23NaR MRI to investigate brain sodium homeostasis and map potential alterations in patients with ALS as compared with healthy controls. Materials and Methods: Seventeen patients with ALS (mean age 61.1 ± 11.4 years, m/f = 9/8) and 10 healthy control subjects (mean age 60.3 ± 15.3 years, m/f = 6/4) were examined by 23NaR MRI at 3 T. Regional sodium maps were obtained by the calculation of the weighted difference from two image data sets with different echo times (TE1 = 0.3 ms, TE2 = 25 ms). Voxel-based analysis of the relaxation-weighted maps, together with 23Na concentration maps for comparison, was performed. Results: ROI-based analyses of relaxation-weighted brain sodium concentration maps demonstrated increased sodium concentrations in the upper corticospinal tracts and in the frontal lobes in patients with ALS; no differences between ALS patients and controls were found in reference ROIs, where no involvement in ALS-associated neurodegeneration could be anticipated. Conclusion: 23NaR MRI mapped regional alterations within disease-relevant areas in ALS which correspond to the stages of the central nervous system (CNS) pathology, providing evidence that the technique is a potential biological marker of the cerebral neurodegenerative process in ALS.

The Value of APTw CEST MRI in Routine Clinical Assessment of Human Brain Tumor Patients at 3T.

BACKGROUND: With fast-growing evidence in literature for clinical applications of chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI), this prospective study aimed at applying amide proton transfer-weighted (APTw) CEST imaging in a clinical setting to assess its diagnostic potential in differentiation of intracranial tumors at 3 tesla (T). METHODS: Using the asymmetry magnetization transfer ratio (MTRasym) analysis, CEST signals were quantitatively investigated in the tumor areas and in a similar sized region of the normal-appearing white matter (NAWM) on the contralateral hemisphere of 27 patients with intracranial tumors. Area under curve (AUC) analyses were used and results were compared to perfusion-weighted imaging (PWI). RESULTS: Using APTw CEST, contrast-enhancing tumor areas showed significantly higher APTw CEST metrics than contralateral NAWM (AUC = 0.82; p < 0.01). In subgroup analyses of each tumor entity vs. NAWM, statistically significant effects were yielded for glioblastomas (AUC = 0.96; p < 0.01) and for meningiomas (AUC = 1.0; p < 0.01) but not for lymphomas as well as metastases (p > 0.05). PWI showed results comparable to APTw CEST in glioblastoma (p < 0.01). CONCLUSIONS: This prospective study confirmed the high diagnostic potential of APTw CEST imaging in a routine clinical setting to differentiate brain tumors.

Cortical activation during a pitch discrimination task in tinnitus patients and controls--an fMRI study.

Chronic subjective tinnitus has been associated with aberrant activation of cortical areas involved in the perception of auditory information. This leads to the hypothesis that neural correlates of altered auditory perception may be found in tinnitus patients using functional magnetic resonance imaging. To study brain activation patterns due to acoustic stimulation in a pitch discrimination task, 6 tinnitus patients and 6 age-matched controls were investigated. Tones were presented binaurally at 5 beeps/s with three different frequencies in a block design. Using Statistical Parametrical Mapping, we found activation of secondary auditory areas in both groups. Furthermore, controls showed activation of the right-hemispheric anterior insula, whereas the middle frontal gyrus, putamen and left-hemispheric insula were activated in tinnitus patients. In the between-group analysis, activation of the caudate nucleus, superior frontal gyrus (Brodmann area 8) and cingular cortex was more pronounced in patients than in controls suggesting the perception of auditory inputs in a more emotional context in our patient group compared to controls.

Graded cutaneous electrical vs thermal stimulation in humans shows different insular and cingulate cortex activation.

Pain can result from various sensory input modalities. To elucidate the differences of cortical responses to graded electrical and thermal stimulation, functional magnetic resonance imaging (fMRI) results of two studies using the same stimulation paradigms but different modalities with 15 healthy subjects each are compared. During painful electrical stimulation contralateral dorsal posterior insula and ventral posterior anterior cingulate cortex (ACC) activated more. During thermal stimulation, there was more activation in ipsilateral primary motor area (MI)/primary sensory area (SI) complex and premotor areas as well as dorsal posterior ACC. Thus electrostimulation preferably activates structures of the lateral pain projection system resulting in contralateral dorsal posterior insula and ventral posterior ACC activation. During thermal stimulation, more dorsal areas of the posterior ACC activated. The activation of ipsilateral MI/SI complex and premotor areas may be attributed to the slower perception of thermal stimuli and resulting re-evaluation. This has to be taken into account in the interpretation of other cross-modality studies as well.

A Signal Acquisition Setup for Ultrashort Echo Time Imaging Operating in Parallel on Unmodified Clinical MRI Scanners Achieving an Acquisition Delay of [Formula: see text].

Ultrashort echo time imaging on clinical systems is still limited by the rather long radio frequency switching times achievable with standard front end concepts. In this contribution, an independent parallel receive-only system is interfaced to an unmodified clinical MRI system, enabling imaging of species with ultrashort relaxation times, such as bone, tendon, teeth, or lung tissue. Synchronization of the system is achieved by an electronically decoupled one-way trigger line, a clock reference signal, and RF pulse tracking, thus ensuring minimal interference with the host system. With the proposed system, an acquisition delay of [Formula: see text] is experimentally demonstrated.

Stress distribution and displacement analysis during an intermaxillary disjunction--a three-dimensional FEM study of a human skull.

The goal of this study was to contribute to an understanding of how much expansion force is needed during a maxillary expansion (ME) and where bony reaction takes place. A finite element (FE) model of a dry human male skull was generated from CT scans. The FE model, which consists of cortical and cancellous bone and teeth, was loaded with the same force magnitudes, directions and working points as in rapid maxillary expansion (RME). A three-dimensional finite element stress analysis (FESA) of the forces and displacement was performed. The highest stress was observed in the maxilla in the region where the forces were applied, and spreads more or less throughout almost the whole frontal skull structures. The displacement distribution which causes stress in the skull is highly dependant on the thickness of the bone and its structure. All areas with high compressive and tensile stress are exactly the regions which determine the maximal amount of force to be used during the maxillary expansion and should be examined in case of any complication during a patient's treatment. Regions with significant compressive and tensile stress are the regions observed to have an increase in cellular activity. Further simulations with a given displacement (0.5mm) showed that displacement simulations need extra caution otherwise they will lead to very high forces which are not realistic in an orthodontic treatment.