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Thomas R Nelson

Publications and source records attributed to Thomas R Nelson.

10 recordsLinked to original sources
PubMed2006

Computed tomography for imaging the breast.

Despite the success of screening mammography contributing to the reduction of cancer mortality, a number of other imaging techniques are being studied for breast cancer screening. In our laboratory, a dedicated breast computed tomography (CT) system has been developed and is currently undergoing patient testing. The breast CT system is capable of scanning the breast with the woman lying prone on a tabletop, with the breast in the pendant position. A 360 degrees scan currently requires 16.6 s, and a second scanner with a 9-second scan time is nearly operational. Extensive effort was placed on computing the radiation dose to the breast under CT geometry, and the scan parameters are selected to utilize the same radiation dose levels as two-view mammography. A total of 55 women have been scanned, ten healthy volunteers in a Phase I trial, and 45 women with a high likelihood of having breast cancer in a Phase II trial. The breast CT process leads to the production of approximately three hundred 512 x 512 images for each breast. Subjective evaluation of the breast CT images reveals excellent anatomical detail, good depiction of microcalcifications, and exquisite visualization of the soft tissue components of the tumor when contrasted against adipose tissues. The use of iodine contrast injection dramatically enhances the visualization of tumors. While a thorough scientific investigation based upon observer performance studies is in progress, initial breast CT images do appear promising and it is likely that breast CT will play some role in breast cancer imaging.

Breast↗
PubMed2006

Preexamination and postexamination assessment of parental-fetal bonding in patients undergoing 3-/4-dimensional obstetric ultrasonography.

OBJECTIVE: The purpose of this study was to determine whether there is a change in parental bonding and couples' attitudes toward their fetus after undergoing 3-/4-dimensional ultrasonography (3D/4DUS). METHODS: Sixty-five fathers and 124 mothers were asked to fill out a maternal-fetal attachment questionnaire relating to how they felt about their fetus before and after 3D/4DUS and to mark on a line indicating their feelings about the ultrasonography experience. In addition, 135 parents filled out a positive feelings questionnaire consisting of 5 sections assessing their feelings about the fetus. The 3D/4DUS examination included rendering of the fetal face, limbs, and thorax. RESULTS: One hundred forty-two patients filled out all questions and were analyzed for the total attachment score. The difference of the total score for the maternal-fetal attachment questionnaire before and after 3D/4DUS had a z value of 5.6 for all patients and was statistically significant (P < .0001). In analyzing each question, 5 were found to have a statistically significantly different score for women, but only 2 were found so for men. The scores for the line, before and after 3D/4DUS, showed a significant difference for men but not women. The women studied did not show a change using this instrument because their median response was at the maximum measurement before their sonograms. The positive feelings questionnaire showed a statistically significant change for women in all sections but for men in only 2. CONCLUSIONS: Parents have a change in attitude regarding their fetus after undergoing 3D/4DUS. Mothers showed an increase in bonding to their fetus after 3D/4DUS in more categories than fathers.

Data Interpretation, Statistical↗
PubMed2005

Endocavitary three-dimensional ultrasonographic assistance for transvaginal or transrectal drainage of pelvic fluid collections.

PURPOSE: Determine the feasibility of using three-dimensional ultrasonography (3D US) to assist in planning and performing endocavitary drainage of deep pelvic fluid collections. MATERIALS AND METHODS: Retrospective review of images and medical records of 16 patients in whom endocavitary 3D US was used during transvaginal or transrectal drainage of 17 deep fluid collections. 3D US was assessed regarding its ability to display the relevant structures, whether new information was provided compared with pelvic computed tomography (CT) and conventional two-dimensional US (2D US) displays, and whether this information altered drainage techniques. RESULTS: Targeted fluid collections were visualized in all patients. 3D US added information in 11 of 16 patients (69%) that, in turn, resulted in adjustment of interventional technique in eight of 16 patients (50%). Specific features of 3D US that provided new information included the simultaneous display of three orthogonal US images, display of reconstructed US image plane orientations not possible with 2D US, and the ability to interactively scroll images through complex structures to assess for communication between the loculations. An attached needle guide was used in 15 of 16 patients to improve the precision of needle placement. CONCLUSION: Endocavitary 3D US is feasible for assistance in transvaginal and transrectal drainage procedures, usually adds new information, frequently alters interventional technique, and permits precise access needle placement.

Abscess↗
PubMed2005

Technique factors and their relationship to radiation dose in pendant geometry breast CT.

The use of breast computed tomography (CT) as an alternative to mammography in some patients is being studied at several institutions. However, the radiation dosimetry issues associated with breast CT are markedly different than in the case of mammography. In this study, the spectral properties of an operational breast CT scanner were characterized both by physical measurement and computer modeling of the kVp-dependent spectra, from 40 to 110 kVp (Be window W anode with 0.30 mm added Cu filtration). Previously reported conversion factors, normalized glandular dose for CT-DgN(ct), derived from Monte Carlo methods, were used in concert with the output spectra of the breast scanner to compute the mean glandular dose to the breast based upon different combinations of x-ray technique factors (kVp and mAs). The mean glandular dose (MGD) was measured as a function of the compressed breast thickness (2-8 cm) and three different breast compositions (0%, 50%, and 100% glandular fractions) in four clinical mammography systems in our institution. The average MGD from these four systems was used to compute the technique factors for breast CT systems that would match the two-view mammographic dose levels. For a 14 cm diameter breast (equivalent to a 5 cm thick compressed breast in mammography), air kerma levels at the breast CT scanner's isocenter (468 mm from the source) of 4.4, 6.4, and 9.0 mGy were found to deliver equivalent mammography doses for 0%, 50%, and 100% glandular breasts (respectively) at 80 kVp. At 80 kVp (where air kerma was 11.3 mGy/100 mAs at the isocenter), 57 mAs (integrated over the entire scan) was required to match the mammography dose for a 14 cm 50% glandular breast. At 50 kVp, 360 mAs is required to match mammographic dose levels. Tables are provided for both air kerma at the isocenter and mAs for 0%, 50%, and 100% glandular breasts. Other issues that impact breast CT technique factors are also discussed.

Biophysical Phenomena↗
PubMed2005

Three- and 4-dimensional ultrasound in obstetrics and gynecology: proceedings of the American Institute of Ultrasound in Medicine Consensus Conference.

The American Institute of Ultrasound in Medicine convened a panel of physicians and scientists with interest and expertise in 3-dimensional (3D) ultrasound in obstetrics and gynecology to discuss the current diagnostic benefits and technical limitations in obstetrics and gynecology and consider the utility and role of this type of imaging in clinical practice now and in the future. This conference was held in Orlando, Florida, June 16 and 17, 2005. Discussions considered state-of-the-art applications of 3D ultrasound, specific clinical situations in which it has been found to be helpful, the role of 3D volume acquisition for improving diagnostic efficiency and patient throughput, and recommendations for future investigations related to the utility of volume sonography in obstetrics and gynecology.

Female↗
PubMed2004

Ultrasonographic modalities to assess vascular anatomy and disease.

Medical ultrasound (US) encompasses a family of imaging techniques linked by the use of high-frequency sound waves, typically 2.5-10 million cycles per second (MHz), to interrogate tissue. Although similar, each imaging technique has relatively distinct features and may provide unique information. This review is designed to provide vascular and interventional radiologists with an in-depth understanding of each US imaging technique and relevant physics principles to assist in optimizing the US examination so that the specific vascular anatomy and disease states in question can be comprehensively understood. This review will be limited to principles of transcutaneous US and will not include specific techniques for assessment of individual vessels (except for illustrative purposes) or methods to optimize US scan parameters.

Arterial Occlusive Diseases↗
PubMed2004

Display of 3-dimensional ultrasonographic images for interventional procedures: volume-rendered versus multiplanar display.

OBJECTIVE: The goal of this project was to assess the display of 3-dimensional ultrasonographic images as used for interventional procedures, particularly the conspicuity of various targets and interventional devices, comparing volume-rendered (VR) versus multiplanar reformatted (MPR) display approaches. METHODS: A series of ultrasonographic phantoms were made from a petroleum gel with cornstarch used to vary the echo texture. Three-dimensional ultrasonographic target and device conspicuity were judged with a 5-point visual rating scale. The MPR image was considered the reference standard. Volume-rendered image conspicuity was judged for combinations of 7 different postprocessing display parameters and compared with MPR images. RESULTS: Definite visualization of the embedded objects occurred in 92% of MPR and 13% of VR test situations (P < .0001). Volume-rendered display was associated with a mean conspicuity degradation of 2.6 on a scale of 0 through 4 (P < .0001) compared with MPR methods. The proportion of satisfactory VR images was greatest in test situations with a large degree of difference of echogenicity between the background medium and the embedded object. The transparent-type postprocessing rendering modes were superior to the surface-type rendering modes (P < .0001). CONCLUSIONS: Current 3-dimensional ultrasonographic MPR imaging display in a solid organ environment provides better visualization performance of target and needle conspicuity than VR image display when there are not large differences in the signal levels of targeted structures and devices compared with surrounding tissues. The difficulty in viewing both target and device with VR imaging may restrict its ability to guide interventional procedures in some clinical situations.

Humans↗
PubMed2003

Three-dimensional ultrasonography for planning percutaneous drainage of complex abdominal fluid collections.

PURPOSE: To identify information provided by three-dimensional (3D) ultrasonography (US) useful for percutaneous drainage of complex abdominal fluid collections. MATERIALS AND METHODS: 3D US evaluation of the collection structure and spatial relationship of items of interest was performed immediately before percutaneous access of 46 complex fluid collections in 26 patients (28 procedures). Procedurally useful information was tabulated and analyzed. RESULTS: In five of 28 procedures (18%), 3D US could not visualize the fluid collections. In 21 of 23 procedures (91%) with adequate US visualization, 3D US provided unique helpful information: in 20 of 21 (95%), the direction of access was selected to favor subsequent manipulation; in 17 of 21 (81%), a single access site could be used for multiple drains; in 17 of 21 (81%), the location of the drain was determined; in 11 of 21 (52%), the number of drains was altered; and in six of 21 (29%), high-risk deep collections were accessed via connections from safer superficial collections. 3D US provided no additional information in two of 23 procedures (9%) and provided misinformation regarding interconnections between collections in two of 23 (9%). Percutaneous drainage was curative in 20 of 26 patients (77%). CONCLUSION: In sonographically suitable situations, 3D US can add substantial information on structure and spatial relationships to optimize initial drainage of complex fluid collections.

Abdominal Abscess↗
PubMed2002

Main portal vein access in transjugular intrahepatic portosystemic shunt procedures: use of three-dimensional ultrasound to ensure safety.

PURPOSE: To document the safety of main portal vein (PV) access to create transjugular portosystemic intrahepatic shunts (TIPS), provided that three-dimensional ultrasonography (3D US) can document the puncture to have entered a surface of the PV suitable for tamponade. MATERIALS AND METHODS: In 11 patients who underwent conventional TIPS creation (n = 10) or a transjugular portacaval shunt procedure (n = 1), the puncture was found angiographically to enter the main PV. In seven cases, this occurred at the PV bifurcation and, in four, it occurred in the superior third of the PV. 3D US was used to determine whether the point of PV entry was functionally intrahepatic or extrahepatic. The puncture site was deemed to be intrahepatic if liver covered the puncture site on all three orthogonal imaging planes (sagittal, coronal, and transverse). If the puncture site was surrounded by liver, the access was used to deploy a metallic stent (uncovered, n = 10; covered, n = 1). Medical records and follow-up cross-sectional imaging studies were reviewed for evidence of hemorrhage complications. Pathologic correlation was performed in one explanted liver and autopsy specimens in five other patients. RESULTS: In nine of 11 patients, 3D US was diagnostic and confidently verified that liver completely covered the portal vein access site. In two patients with diagnostically uncertain 3D US results, transcatheter injection of contrast medium documented no extravasation. All TIPS and direct portacaval shunt procedures were technically successful. No hemorrhagic complications occurred. Examination of pathologic specimens documented this portion of the portal vein to be extraperitoneal, but attached to the superior surface of the caudate lobe with fibrous tissue and small portal vein branches. CONCLUSIONS: The bifurcation and posterior aspect of the superior third of the main PV can be safely used for TIPS procedures, provided access is proven to be surrounded by liver. 3D US can usually confidently determine if the PV entry site is functionally intrahepatic.

Adult↗