Automated lung outline reconstruction in ventilation-perfusion scans using principal component analysis techniques.

The present work addresses the development of an automated software-based system utilized in order to create an outline reconstruction of lung images from ventilation-perfusion scans for the purpose of diagnosing pulmonary embolism. The proposed diagnostic software procedure would require a standard set of digitized ventilation-perfusion scans in addition to correlated chest X-rays as key components in the identification of an ideal template match used to approximate and reconstruct the outline of the lungs. These reconstructed lung images would then be used to extract the necessary PIOPED-compliant features which would warrant a pulmonary embolism diagnosis. In order to evaluate this issue, two separate principal component analysis (PCA) algorithms were employed independently, including Eigenlungs, which was adapted from the Eigenfaces method, and an artificial neural network. The results obtained through MATLAB(TM) simulation indicated that lung outline reconstruction through the PCA approach carries significant viability.

Radiation oncology practice accreditation.

The practice accreditation program of The American College of Radiology is described. Practice accreditation constitutes a facile mechanism to accomplish external quality assurance and to assess compliance with recognized standards. The process of accreditation includes critical review of each radiation therapy facility, the technical staff, all quality assurance procedures, medical physics staff, nursing and physician personnel as well as a whole host of other items, the most important of which is meticulous examination of selected patient charts. In the appendix, standards developed by the American College of Radiation Oncology, are reported.

Accuracy of magnetic resonance imaging stereotactic coordinates with the cosman-roberts-wells frame.

Quality assessment on the accuracy of a Cosman-Roberts-Wells (CRW) magnetic resonance imaging (MRI) stereotactic ring which had nonferrous stainless steel screws and positioning posts and a localizer with petroleum jelly in the fiducials, purchased in 1994, revealed errors of greater than 4 mm with targets in phantoms. Image fusion of objects within the phantom indicated the central area was accurately depicted by CT or MRI. We then tested a newer CRW- MRI ring (MRIA-IHR with titanium screws and posts) and localizer (MRIA-2-LF with fiducials filled with copper sulfate) and found that the MRI stereotactically calculated target coordinates matched both the known position of these targets in the phantom as well as the CT stereotactically calculated coordinates within approximately 1 mm. We also describe excellent superimposition of CT and MRI stereotactically determined surfaces in a recent clinical case using the new hardware. This shows that recent modifications to the CRW-MRI stereotactic system can make it accurate for small targets, but we emphasize that all systems need to undergo ongoing local quality assessment to ensure acceptable accuracy in practice.

Clinical fusion of three-dimensional images using Bremsstrahlung SPECT and CT.

UNLABELLED: Infusional brachytherapy for treatment of neoplasms, with colloidal 32P has been used to treat various tumors in the pancreas, liver, brain, lung, and head and neck. In performing such treatments, anatomical verification of the location of the administered 32P from the image obtained by Bremsstrahlung SPECT alone is not possible due to the lack of internal landmarks, since the radionuclide is distributed only in the tumor and does not usually accumulate in the normal organs. The purpose of this study was to provide a practical three-dimensional approach for image fusion between Bremsstrahlung SPECT and CT. METHODS: The tumors in four cancer patients were injected directly with 32P under CT guidance. A Bremsstrahlung SPECT study using 99mTc backscatter sources to obtain the body contour was then performed. SPECT images were used to generate the skin contours using a threshold detection method. A three-dimensional surface was generated from these contours using a tiling program and fused with a corresponding CT surface generated from a CT scan in the same patient through an iterative surface-fitting algorithm. The three-dimensional surface of the region of high-activity, corresponding to the infused tumor, was then generated using the Bremsstrahlung SPECT data by mapping the iso-count surfaces through a computer program. The three-dimensional image of the organ then was fused with the registered CT-SPECT datasets. RESULTS: The accuracy of fit measured as the mean distance between the SPECT and CT surfaces was in the range of 3-4 mm. CONCLUSION: The anatomical co-registration of Bremsstrahlung SPECT with CT images using the outer surface-fitting algorithm is a reliable tool. This correlation permits direct anatomic confirmation of the region of the 32P activity distribution with the anatomic site selected for injection.

Quantitative assessment of beam perturbations caused by silicon diodes used for in vivo dosimetry.

PURPOSE: To measure the effect of silicon diode detectors used for in vivo dosimetry on beam characteristics and determine whether this effect is clinically significant. METHODS AND MATERIALS: Commercially available photon and electron diodes were placed on the central axis of photon and electron beams. The beam characteristics were measured for 6- and 10-MV photon and 6-20-MeV electron energies from a Varian Clinac 1800 medical linear accelerator. Water was used for the medium, and measurements were made for various clinically common field sizes and depths. RESULTS: Beam attenuations along the central axis were 10 and 7.5% for 6- and 10-MV photons, respectively. Electron beam dose reductions were between 13 and 25% for 20-6-MeV electrons. Photon beam flatness varied up to 7% at different depths, but the symmetry was not affected much. Electron beam flatness and symmetry were significantly changed to as much as 18 and 6%, respectively. CONCLUSION: Use of diode detectors on central axis of photon and electron beams for in vivo dosimetry causes significant attenuation and alteration of the beam characteristics. The percentage of the volume affected is significant (e.g., 23% of the volume in a 4 x 4 field gets 10% less dose for a 6-MV photon beam), especially if these diodes are used for in vivo dosimetry on the central axis every day for every treatment, as is done in some clinics. Other beam parameters such as penumbra and skin dose are also affected. It is therefore recommended that the diodes be used only as needed.