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PubMed1998

Combining various projection access schemes with the algebraic reconstruction technique for low-contrast detection in computed tomography.

We separately applied three different projection access orders (the multilevel scheme (MLS), the sequence access scheme (SAS) and the random permutation scheme (RPS)) to the algebraic reconstruction technique (ART) in an attempt to improve low-contrast object detection in computed tomography (CT). We used both simulated (from various numbers of projections of low-contrast and contrast detail phantoms) and actual data (from megavoltage portal CT) during our study. When coupled with ART, SAS and RPS led to poor low-contrast detection and required multiple iterations for convergence. In contrast, one-iteration MLS yielded the most uniform reconstructions with the highest contrast-to-noise ratios. Therefore, MLS-ART provides the highest dose efficiency of all current reconstruction techniques for imaging low-contrast objects from a small number of projections.

Algorithms↗

PubMed2005

Comparison between CT-based volumetric calculations and ICRU reference-point estimates of radiation doses delivered to bladder and rectum during intracavitary radiotherapy for cervical cancer.

PURPOSE: To compare CT-based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the bladder and rectum in patients with carcinoma of the uterine cervix treated with definitive low-dose-rate intracavitary radiotherapy (ICRT). METHODS AND MATERIALS: Between November 2001 and March 2003, 60 patients were prospectively enrolled in a pilot study of ICRT with CT-based dosimetry. Most patients underwent two ICRT insertions. After insertion of an afterloading ICRT applicator, intraoperative orthogonal films were obtained to ensure proper positioning of the system and to facilitate subsequent planning. Treatments were prescribed using standard two-dimensional dosimetry and planning. Patients also underwent helical CT of the pelvis for three-dimensional reconstruction of the radiation dose distributions. The systems were loaded with 137Cs sources using the Selectron remote afterloading system according to institutional practice for low-dose-rate brachytherapy. Three-dimensional dose distributions were generated using the Varian BrachyVision treatment planning system. The rectum was contoured from the bottom of the ischial tuberosities to the sigmoid flexure. The entire bladder was contoured. The minimal doses delivered to the 2 cm3 of bladder and rectum receiving the highest dose (DBV2 and DRV2, respectively) were determined from dose-volume histograms, and these estimates were compared with two-dimensionally derived estimates of the doses to the corresponding ICRU reference points. RESULTS: A total of 118 unique intracavitary insertions were performed, and 93 were evaluated and the subject of this analysis. For the rectum, the estimated doses to the ICRU reference point did not differ significantly from the DRV2 (p = 0.561); the mean (+/- standard deviation) difference was 21 cGy (+/- 344 cGy). The median volume of the rectum that received at least the ICRU reference-point dose was 2.1 cm3. In 66 (71%) of 93 cases, <5 cm3 was treated to this dose. However, for the bladder, the estimated doses to the ICRU reference point were significantly lower than the D(BV2) (p <0.001); the mean difference was 680 cGy (+/- 543 cGy). The median volume of the bladder that received at least the ICRU reference-point dose was 13.0 cm3. CONCLUSIONS: Our data suggest that the estimated dose to the ICRU rectal point may be a reasonable surrogate for the DRV2. However, this result may not be applicable to other treatment guidelines and ICRT applicator systems. In contrast, the dose to the ICRU bladder point does not appear to be a reasonable surrogate for the DBV2. Correlation with late complications are needed to define the role of three-dimensional dosimetry in treatment planning.

Brachytherapy↗

PubMed1990

Simultaneous reconstruction of cervical soft tissue and esophagus with a gastro-omental free flap.

A microvascular transfer of gastric tube and omentum was used to simultaneously reconstruct cervical soft-tissue and esophageal defects in five patients. All patients had previous high-dose radiation and multiple flap reconstructions. The largest esophageal and soft-tissue defects were 10 cm and 160 cm2, respectively. All wounds healed primarily except for one orocutaneous fistula. There was one death from an intraoperative stroke. The gastro-omental flap is useful in cases where the reconstructive surgeon is faced with both esophageal and soft-tissue defects--particularly in heavily irradiated patients who have few reconstructive options.

Anastomosis, Surgical↗

PubMed1997

Microvascular free tissue transfers after preoperative irradiation in head and neck reconstructions.

Surgical reconstruction of large head and neck tumors involves great problems. Preoperative irradiation increases the risk of postoperative complications. The use of microvascular free flaps has definitive advantages over conventional reconstruction techniques and permits immediate preoperative high-dose radiation therapy. Eighty-eight patients, 55 (62%) men and 33 (38%) women, with head and neck tumors underwent microvascular reconstruction at the Turku University Central Hospital in 1985-1995; 77 of them were irradiated before surgery. All irradiated patients underwent primary reconstruction. The preoperative radiation dose was 50-65 Gy. The free tissue transfer was successful in 77 (88%) of the 88 patients. The success rate was 87% in irradiated patients and 91% in nonirradiated patients. Free tissue transfers are suitable for one-stage reconstruction in selected patients such as those receiving high-dose preoperative irradiation. The transfer of microvascular free flaps to the head and neck has become the most common reconstruction method owing to its increasing success rates as well as its excellent esthetic and functional results.

Female↗

PubMed2005

Optimized image reconstruction for detection of deep venous thrombosis at multidetector-row CT venography.

The aims of this study were to optimize image quality for indirect CT venography (sequential versus spiral), and to evaluate different image reconstruction parameters for patients with suspected deep venous thrombosis (DVT). Fifty-one patients (26/25 with/without DVT) were prospectively evaluated for pulmonary embolism (PE) with standard multidetector-row computed tomography (MDCT) protocols. Retrospective image reconstruction was done with different slice thicknesses and reconstruction increments in sequential and spiral modes. All reconstructions were read for depiction of DVT and to evaluate best reconstruction parameters in comparison with the thinnest reconstruction ("gold standard"). Image noise and venous enhancement were measured as objective criteria for image quality. Subjective image quality was rated on a four-point scale. Effective dose was estimated for all reconstructions. In sequential 10/50 reconstruction DVT was completely detected in 13/26 cases, partially in 10/26 cases and was not detected at all in 3/26 cases, and 15/26, 9/26 and 2/26 cases for the 10/20 reconstruction, respectively. DVT was completely detected in all spiral reconstructions. Image noise ranged between 14.8-29.1 HU. Median image quality was 2. Estimated effective dose ranged between 2.3 mSv and 11.8 mSv. Gaps in sequential protocols may lead to false negative results. Therefore, spiral scanning protocols for complete depiction of DVT are mandatory.

Adult↗

PubMed2004

Three-dimensional point localisation in low-dose X-ray images using stereo-photogrammetry.

A stereo-photogrammetric method for three-dimensional reconstruction of points in low-dose digital X-ray images obtained using a scanner with similar imaging geometry to that of computed tomography scan projection radiography, was analysed. A calibration frame containing 25 radio-opaque markers with known three-dimensional locations was scanned, and the accuracy of reconstruction of the marker positions under varying control point configurations and separation angles was assessed. Errors of less than 1 mm were obtained when nine test points were reconstructed, with 16, 11 and 7 control points at a 90 degrees separation angle, and with 16 and 11 control points at 75 degrees and 60 degrees separation angles. The optimum reconstruction, with a resultant error of 0.68 mm, was found to occur at a separation angle of 90 degrees, with the largest number of control points (16) used to calculate the parameters of the transformation. Extrapolation in the scanning direction beyond the space defined by the control points gave errors of less than 2 mm. This method should be suitable for three-dimensional point reconstruction in applications such as cephalometry, brachytherapy planning and assessment of spinal shape.

Humans↗

PubMed1991

Clinical spectrum of fungal infections after orthotopic liver transplantation.

During a 50-month period, we identified 91 episodes of fungal infection in 72 liver transplant recipients (23.8%). Candida species accounted for 83.5% of cases. Clinical patterns of fungal infections included disseminated infection (19), peritonitis (17), pneumonitis (15), multiple sites of colonization (13), fungemia (11), and other sites (16). The diagnosis of fungal infection was usually made in the first 2 months (84.7% of cases), at a mean time of 16 days after transplantation. Risk factors for fungal infections included retransplantation, Risk score, intraoperative transfusion requirement, urgent status, Roux limb biliary reconstruction (in adults), steroid dose, bacterial infections and antibiotic therapy, and vascular complications. Fungal infections were successfully treated with amphotericin B in 63 cases (74.1%) but were associated with diminished patient survival (50% vs 83.5%). Fungal infection is a frequent source of early morbidity and can be related to well-defined risk factors, suggesting the need for effective prophylaxis.

Adolescent↗

PubMed1997

Identification of spherical virus particles in digitized images of entire electron micrographs.

New methods are described that should facilitate high-resolution (5-10 A) image reconstructions from low-dose, low-contrast electron micrographs of frozen-hydrated specimens and processing of large, digital images produced by new imaging devices and modern electron microscopes. Existing techniques for automatic selection of images of individual biological macromolecules from electron micrographs are inefficient or unreliable. We describe the Crosspoint method (CP), which produces good quality solutions with relatively small miss rates and few false hits, and an extension of this method along with a procedure for refining its solution. Two algorithms for processing large images, one based on image subsampling, the other on image decomposition, are described. A large image is first compressed (e.g., by subsampling) and the CP method is applied to the compressed image to produce an initial solution. The information gathered at this stage is used to cut the original image into subimages and then to refine the particle coordinates in each subimage. An interactive environment for experimenting with particle identification methods is described.

Algorithms↗

PubMed2004

[Staging of multiple myeloma with MRI: comparison to MSCT and conventional radiography].

The staging of patients with multiple myeloma demands sensitive imaging methods for the assessment of the skeletal system. MRI allows for direct visualization of the bone marrow which exhibits five different infiltration patterns in multiple myeloma: 1. normal appearance of the bone marrow, 2. focal involvement, 3. homogeneous diffuse infiltration, 4. combined diffuse and focal infiltration, 5. "salt and pepper" pattern with inhomogeneous bone marrow signals due to multiple fat islands. The combination of T1w-SE and STIR sequences is best suited for detecting all infiltration patterns and for the differential diagnoses e. g. hemangiomas. With parallel imaging in MRI, acquisition times can be markedly reduced and whole-body screening of the bone marrow can be achieved within 30 min. MRI is superior to radiography for the detection of focal as well as diffuse infiltration. Multidetector computed tomography and especially 16- and 64-detector row scanners allow fast imaging with thin slice collimation and multiplanar reconstructions. With low-dose protocols, effective dose reduction can be achieved, so that radiation exposure is only slightly higher than that of a whole-body skeletal x-ray exam. Sensitivity of MSCT is markedly superior to conventional radiography. Due to the direct visualization of the bone marrow with MRI, MRI is superior in detecting early infiltrations with myeloma cells without osteolyses. In advanced multiple myeloma, CT on the other hand, enables for more precise assessment of bony destructions and fracture risk.

Adult↗

PubMed1995

Reconstructive airway operation after irradiation.

After a patient died of anastomotic necrosis following a tracheal resection for the management of recurrent thyroid cancer invading the trachea, which had been treated 6 years previously by thyroid lobectomy and 4,800 cGy of radiation to control known residual disease, we explored methods to promote the healing of tissues damaged by irradiation. Between 1979 and 1992, 22 patients underwent major airway resection and reconstruction after receiving large doses of radiation. The average dose was 4,979 +/- 1,113 cGy (range, 3,150 to 6,840 cGy); the number of fractions, 20 to 38; and the average dose per fraction, 180 cGy (range, 150 to 200 cGy). The interval between irradiation and surgical treatment was 42 +/- 105 months (range, 1 to 480 months). Seven cervical, eight midtracheal, and five carinal resections were performed, as well as two mainstem sleeve resections. Omentum was used to protect the anastomosis in 15 patients (68%), a pericardial fat pad was used in 2, and pleura was used in 2. In 3 patients, sternohyoid muscle was placed between the anastomosis and a major vascular structure, but without a tissue wrap. Two patients (9.0%) died postoperatively. Anastomotic dehiscence was the cause of death in a patient treated for lymphoma, and adult respiratory distress syndrome was the cause in the other patient; this patient had undergone carinal pneumonectomy. Complications developed in 8 patients (36%). Two cervical dehiscences were treated by T-tube placement, 2 patients suffered wound infection, and 1 patient each suffered a myocardial infarction, dysphagia, hemoptysis, and bronchitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed2006

Synovial cell sarcoma of the vulva: multimodality treatment incorporating preoperative external-beam radiation, hemivulvectomy, flap reconstruction, interstitial brachytherapy, and chemotherapy.

BACKGROUND: Vulvar synovial cell sarcomas are rare, with only four previously published cases in the literature. Traditionally, the primary management for these tumors has been surgery alone. CASE: We report a case of a large vulvar synovial cell sarcoma in a 50-year-old woman treated with comprehensive combined multimodality management, including preoperative intensity-modulated radiation therapy, radical hemivulvectomy, flap reconstruction, interstitial low-dose-rate brachytherapy boost, and adjuvant chemotherapy. CONCLUSION: Based on this case and the limited data in the literature, multimodality treatment of advanced soft tissue sarcoma of the vulva may optimize local control and minimize toxicity while preserving sexual function.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2001

A systemic biokinetic model for polonium.

Although the biokinetics of polonium has been studied extensively, interpretation of the data is complicated by potential differences with species and route of exposure and the questionable reliability of much of the reported excretion data for man. A study was undertaken to identify the data that are most likely to represent the typical behavior of polonium and apply those data to construct an improved, physiologically realistic systemic biokinetic model for polonium in man. Such a model is needed for interpretation of urinary excretion data for workers exposed to 210Po and reconstruction of the radiation doses received by those workers. This paper reviews the database on the biokinetics of polonium and describes a new systemic biokinetic model for polonium in man.

Air Pollutants, Occupational↗

PubMed2000

Thyroid cancer following exposure to radioactive iodine.

The thyroid gland is one of the most sensitive organs for radiation-induced oncogenesis and the magnitude of the risk from external radiation is well understood. This is not the case for internal radiation derived from the radioiodines, a matter of practical importance because of medical use and potential accidental exposure. This article reviews current knowledge derived from the follow-up of patients receiving diagnostic or therapeutic 131I and populations exposed to radioactive fallout. The latter includes the nuclear power station accident at Chernobyl and the results of atomic bomb development and testing at Hanford, the Nevada Test Site and the Marshall Islands. The most cogent information comes from Chernobyl where an epidemic of childhood thyroid cancer has followed exposure to radioiodine that was mainly 131I. Although much has been learned from this experience about the nature of radioiodine induced thyroid cancer in young children, the reconstruction of thyroid radiation doses is too preliminary to provide accurate knowledge of the risk in comparison to that from external radiation. In the Marshall Islands, much of the exposure was from short-lived radioiodines as well as external radiation, obviating the possibility to determine the risk from 131I. Exposure to 131I in the continental United States from atomic bomb testing is expected to have caused some thyroid cancers, but only in the immediate vicinity of the Nevada Test Site has any evidence of radiation-induced thyroid neoplasms been adduced. This evidence is minimally significant statistically, and not significant for thyroid cancer per se. Medical use of radioiodine has not been observed to cause thyroid cancer but very few of the patients studied were young children, the group most sensitive to thyroid radiation. Despite these limitations, this information is sufficient to make some suggestions concerning protective measures in the case of nuclear accidents and the follow up of individuals who have been exposed.

Humans↗

PubMed1994

[The spiral CT of orbital space-occupying lesions: improved imaging possibilities via freely reconstructible planes].

In a prospective study the value of spiral CT for the detection and differential diagnosis of intraorbital masses was investigated. Thirty patients with various orbital diseases were examined with transverse spiral computed tomography. After performing two contiguous 1 mm spiral CT scans, coronal, parasagittal, and other reconstructions were obtained. Compared with separately generated 2 mm slices, the 1 mm spiral CT images showed a slightly decreased signal-to-noise ratio, but due to the better spatial resolution, the image quality of secondary reconstructions was similar to that of the original transverse spiral CT slices. Generally the orbital masses were visualized best in the coronal reconstruction. In certain cases, the parasagittal reconstructions were superior. Reconstructions in freely definable slice planes based on 1 mm spirals provides better visualization of orbital diseases without increasing radiation dose. This method allows multiplanar reconstructions similar to magnetic resonance tomography.

Adolescent↗

PubMed2006

A BPF-type algorithm for CT with a curved PI detector.

Helical cone-beam CT is used widely nowadays because of its rapid scan speed and efficient utilization of x-ray dose. Recently, an exact reconstruction algorithm for helical cone-beam CT was proposed (Zou and Pan 2004a Phys. Med. Biol. 49 941-59). The algorithm is referred to as a backprojection-filtering (BPF) algorithm. This BPF algorithm for a helical cone-beam CT with a flat-panel detector (FPD-HCBCT) requires minimum data within the Tam-Danielsson window and can naturally address the problem of ROI reconstruction from data truncated in both longitudinal and transversal directions. In practical CT systems, detectors are expensive and always take a very important position in the total cost. Hence, we work on an exact reconstruction algorithm for a CT system with a detector of the smallest size, i.e., a curved PI detector fitting the Tam-Danielsson window. The reconstruction algorithm is derived following the framework of the BPF algorithm. Numerical simulations are done to validate our algorithm in this study.

Algorithms↗

PubMed2002

Elevated exposure rates under inclined birch trees indicate the occurrence of rainfall during radioactive fallout from Chernobyl.

Knowledge of the mode of deposition (wet or dry) during the main fallout period following the Chernobyl accident in late April 1986 is one of the most important parameters in environmental reconstruction of the radiation dose to the thyroid from 113I following the accident. Meteorological data are available only for a small number of locations, but routine field measurements in 1997 of exposure rates in areas still contaminated by 137Cs revealed that there is a natural indicator of wet deposition. Follow-up measurements confirmed that there is a significant difference in exposure rates measured on different sides at the bases of inclined birch trees in areas of wet deposition. In such areas, the exposure rates measured on the "sheltered" sides of the trees were on average 2.3+/-0.2 times those measured on the unsheltered side. In areas of dry deposition the comparable ratio was 1.01+/-0.02 for similarly inclined trees. Because birch trees are a common feature in the contaminated territories, this effect has a wide potential for use in determining whether the fallout in many areas was due to wet or dry deposition.

Environmental Exposure↗

PubMed2002

Historical overview of atmospheric nuclear weapons testing and estimates of fallout in the continental United States.

From 1945 to 1980, over 500 weapons tests were conducted in the atmosphere at a number of locations around the world. These tests resulted in the release of substantial quantities of radioactive debris to the environment. Local, intermediate, and global fallout deposition densities downwind from test sites depended on the heights of bursts, the yields, and the half-lives and volatilities of the particular fission or activation products, as well as on the meteorological conditions. A number of national and international monitoring programs were established to trace the fallout through the atmosphere and biosphere. These programs included continuous monitoring of ground-level air, exposure rates, and deposition as well as periodic sampling of food, bone, water, soil, and stratospheric air. Although data for specific high-yield tests are still classified, the fission and fusion yields of the various tests and test series have been estimated and from this information the quantities of specific fission and activation products released into the atmosphere have been determined. The geographic and temporal variations in the fallout deposition of specific radionuclides based on both actual measurements and model calculations are discussed in this paper. A feasibility study to estimate the deposition density (deposition per unit area) of particular radionuclides from both Nevada Test Site and "global" fallout on a county-by-county scale for the continental United States is described. These deposition estimates provide a basis for reconstructing population exposure and dose. They support the feasibility of a more detailed evaluation of the population doses that resulted from fallout from atmospheric tests to document the experience fully and to report results more systematically and completely to the world community. The impact of weapons fallout will continue to be felt for years to come since a contaminant baseline has been imposed on the ambient radiation environment that will be an important factor in the assessment of past and future releases of radioactive materials into the biosphere.

Atmosphere↗

PubMedDate not supplied

Osteosarcoma associated with absent thumbs: a report of two cases.

An 8-year-old Hispanic boy with a hypoplastic left thumb, absent right thumb, and short stature experienced right leg pain and limp. A right tibial lesion was imaged and found to be osteosarcoma on biopsy. A 6-year-old Hispanic girl with congenitally absent thumbs experienced a pathologic fracture of her left femur after a minor sports injury. The radiologic abnormality seen was diagnosed as osteosarcoma on biopsy. Both patients continue to do well after intensive preoperative and postoperative high-dose chemotherapy and definitive reconstructive limb surgery. Osteosarcoma has been linked to several congenital syndromes in which absent thumbs are a feature. These two patients with absent thumbs and no definable syndrome experiencing osteosarcoma suggest that congenitally absent thumbs might be a risk factor for osteosarcoma in the absence of a syndrome.

Bone Neoplasms↗