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1.
Phys Med Biol ; 63(7): 075010, 2018 03 27.
Article in English | MEDLINE | ID: mdl-29493533

ABSTRACT

The design, construction and application of a multimodality, 3D magnetic resonance/computed tomography (MR/CT) image distortion phantom and analysis system for stereotactic radiosurgery (SRS) is presented. The phantom is characterized by (1) a 1 × 1 × 1 (cm)3 MRI/CT-visible 3D-Cartesian grid; (2) 2002 grid vertices that are 3D-intersections of MR-/CT-visible 'lines' in all three orthogonal planes; (3) a 3D-grid that is MR-signal positive/CT-signal negative; (4) a vertex distribution sufficiently 'dense' to characterize geometrical parameters properly, and (5) a grid/vertex resolution consistent with SRS localization accuracy. When positioned correctly, successive 3D-vertex planes along any orthogonal axis of the phantom appear as 1 × 1 (cm)2-2D grids, whereas between vertex planes, images are defined by 1 × 1 (cm)2-2D arrays of signal points. Image distortion is evaluated using a centroid algorithm that automatically identifies the center of each 3D-intersection and then calculates the deviations dx, dy, dz and dr for each vertex point; the results are presented as a color-coded 2D or 3D distribution of deviations. The phantom components and 3D-grid are machined to sub-millimeter accuracy, making the device uniquely suited to SRS applications; as such, we present it here in a form adapted for use with a Leksell stereotactic frame. Imaging reproducibility was assessed via repeated phantom imaging across ten back-to-back scans; 80%-90% of the differences in vertex deviations dx, dy, dz and dr between successive 3 T MRI scans were found to be ⩽0.05 mm for both axial and coronal acquisitions, and over >95% of the differences were observed to be ⩽0.05 mm for repeated CT scans, clearly demonstrating excellent reproducibility. Applications of the 3D-phantom/analysis system are presented, using a 32-month time-course assessment of image distortion/gradient stability and statistical control chart for 1.5 T and 3 T GE TwinSpeed MRI systems.


Subject(s)
Algorithms , Imaging, Three-Dimensional/instrumentation , Magnetic Resonance Imaging/instrumentation , Neoplasms/diagnostic imaging , Phantoms, Imaging , Radiosurgery/methods , Tomography, X-Ray Computed/instrumentation , Equipment Design , Humans , Imaging, Three-Dimensional/methods , Magnetic Resonance Imaging/methods , Neoplasms/surgery , Reproducibility of Results , Tomography, X-Ray Computed/methods
2.
Phys Med Biol ; 55(22): 6601-15, 2010 Nov 21.
Article in English | MEDLINE | ID: mdl-20962365

ABSTRACT

The purpose of this study is to develop a geometrically accurate imaging protocol at 3 T magnetic resonance imaging (MRI) for stereotactic radiosurgery (SRS) treatment planning. In order to achieve this purpose, a methodology is developed to investigate the geometric accuracy and stability of 3 T MRI for SRS in phantom and patient evaluations. Forty patients were enrolled on a prospective clinical trial. After frame placement prior to SRS, each patient underwent 3 T MRI after 1.5 T MRI and CT. MR imaging protocols included a T1-weighted gradient echo sequence and a T2-weighted spin echo sequence. Phantom imaging was performed on 3 T prior to patient imaging using the same set-up and imaging protocols. Geometric accuracy in patients and phantoms yielded comparable results for external fiducial reference deviations and internal landmarks between 3 T and 1.5 T MRI (mean ≤ 0.6 mm; standard deviation ≤ 0.3 mm). Mean stereotactic reference deviations between phantoms and patients correlated well (T1: R = 0.79; T2: R = 0.84). Statistical process control analysis on phantom QA data demonstrated the stability of our SRS imaging protocols, where the geometric accuracy of the 3 T SRS imaging protocol is operating within the appropriate tolerance. Our data provide evidence supporting the spatial validity of 3 T MRI for targeting SRS under imaging conditions investigated. We have developed a systematic approach to achieve confidence on the geometric integrity of a given imaging system/technique for clinical integration in SRS application.


Subject(s)
Magnetic Resonance Imaging/methods , Radiosurgery/methods , Radiotherapy Planning, Computer-Assisted/methods , Humans , Phantoms, Imaging
3.
Dentomaxillofac Radiol ; 34(5): 285-91, 2005 Sep.
Article in English | MEDLINE | ID: mdl-16120878

ABSTRACT

OBJECTIVES: Magnetic resonance imaging (MRI) is not routinely used for dental implant planning. A prerequisite for dental implant planning is the accurate imaging of risk structures like the mandibular nerve. The geometric accuracy of the imaging of the mandibular nerve was investigated. METHODS: Two human cadaver heads were scanned using MRI. Computed tomography (CT) scans of the same heads were used as a benchmark. Using a stereotactic frame, corresponding images of MRI and CT were superimposed and the concordance of the images of the mandibular nerve in MRI with those of the mandibular canal in CT was assessed. RESULTS: The geometric accuracy of the mandibular nerve in MRI was as good as that of the mandibular canal in CT imaging. CONCLUSIONS: MRI of the mandibular nerve is sufficiently accurate for the use of this imaging method in dental implant planning.


Subject(s)
Magnetic Resonance Imaging , Mandibular Nerve/anatomy & histology , Artifacts , Cadaver , Humans , Image Processing, Computer-Assisted/methods , Magnetic Resonance Imaging/statistics & numerical data , Mandible/anatomy & histology , Mandible/diagnostic imaging , Mandibular Nerve/diagnostic imaging , Patient Care Planning , Stereotaxic Techniques/instrumentation , Tomography, X-Ray Computed
4.
Stereotact Funct Neurosurg ; 82(5-6): 235-43, 2004.
Article in English | MEDLINE | ID: mdl-15637445

ABSTRACT

The new DIN ('Deutsche Industrie-Norm') 6875-1, which is currently being finalised, deals with quality assurance (QA) criteria and tests methods for linear accelerator and Gamma Knife stereotactic radiosurgery/radiotherapy including treatment planning, stereotactic frame and stereotactic imaging and a system test to check the whole chain of uncertainties. Our existing QA program, based on dedicated phantoms and test procedures, has been refined to fulfill the demands of this new DIN. The radiological and mechanical isocentre corresponded within 0.2 mm and the measured 50% isodose lines were in agreement with the calculated ones within less than 0.5 mm. The measured absorbed dose was within 3%. The resultant output factors measured for the 14-, 8- and 4-mm collimator helmet were 0.9870 +/- 0.0086, 0.9578 +/- 0.0057 and 0.8741 +/- 0.0202, respectively. For 170 consecutive tests, the mean geometrical accuracy was 0.48 +/- 0.23 mm. Besides QA phantoms and analysis software developed in-house, the use of commercially available tools facilitated the QA according to the DIN 6875-1 with which our results complied.


Subject(s)
Radiosurgery/instrumentation , Radiosurgery/standards , Quality Control , Radiosurgery/methods
5.
AANA J ; 66(2): 183-6, 1998 Apr.
Article in English | MEDLINE | ID: mdl-9801481

ABSTRACT

The low solubility of desflurane has been shown to contribute to faster awakening from anesthesia when compared with other anesthetics in common use. However, research has failed to consistently demonstrate faster discharge times from the postanesthesia care unit following the use of desflurane. This study was undertaken to compare the recovery and discharge times of outpatients undergoing procedures greater than 2 hours in length. Thirty-three patients aged 18 to 70 years were randomized to receive either desflurane or isoflurane following a standard intravenous induction with propofol. Patients received premedication and opioids consistent with institutional practice, and inhalation agents were titrated to effect during anesthetic maintenance. Following surgery, patients were evaluated for time to emergence and time to meeting discharge criteria. The results demonstrated no differences between the emergence or discharge times following desflurane or isoflurane. In addition, measured parameters, such as intraoperative vital signs and postoperative emesis and opioid requirements, were not different between the groups. The use of desflurane as part of a balanced anesthetic technique did not speed the emergence or discharge time when compared with isoflurane.


Subject(s)
Anesthetics, Inhalation/therapeutic use , Isoflurane/analogs & derivatives , Isoflurane/therapeutic use , Wakefulness/drug effects , Adult , Ambulatory Surgical Procedures , Desflurane , Female , Humans , Male , Patient Discharge , Time Factors
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