William B. Eubank

PET-CT image registration in the chest using free-form deformations

We have implemented and validated an algorithm for three-dimensional positron emission tomography transmission-to-computed tomography registration in the chest, using mutual information as a similarity criterion. Inherent differences in the two imaging protocols produce significant nonrigid motion between the two acquisitions. A rigid body deformation combined with localized cubic B-splines is used to capture this motion. The deformation is defined on a regular grid and is parameterized by potentially several thousand coefficients. Together with a spline-based continuous representation of images and Parzen histogram estimates, our deformation model allows closed-form expressions for the criterion and its gradient. A limited-memory quasi-Newton optimization algorithm is used in a hierarchical multiresolution framework to automatically align the images. To characterize the performance of the method, 27 scans from patients involved in routine lung cancer staging were used in a validation study. The registrations were assessed visually by two expert observers in specific anatomic locations using a split window validation technique. The visually reported errors are in the 0- to 6-mm range and the average computation time is 100 min on a moderate-performance workstation.

Nonrigid multimodality image registration

We have designed, implemented, and validated an algorithm capable of 3D PET-CT registration in the chest, using mutual information as a similarity criterion. Inherent differences in the imaging protocols produce significant non-linear motion between the two acquisitions. To recover this motion, local deformations modeled with cubic B-splines are incorporated into the transformation. The deformation is defined on a regular grid and is parameterized by potentially several thousand coefficients. Together with a spline-based continuous representation of images and Parzen histogram estimates, the deformation model allows for closed-form expressions of the criterion and its gradient. A limited-memory quasi-Newton optimization package is used in a hierarchical multiresolution framework to automatically align the images. To characterize the performance of the algorithm, 27 scans from patients involved in routine lung cancer screening were used in a validation study. The registrations were assessed visually by two observers in specific anatomic locations using a split window validation technique. The visually reported errors are in the 0-6mm range and the average computation time is 100 minutes.

18Fluorodeoxyglucose Positron Emission Tomography to Detect Mediastinal or Internal Mammary Metastases in Breast Cancer

PURPOSE To determine the prevalence of suspected disease in the mediastinum and internal mammary (IM) node chain by 18fluorodeoxyglucose (FDG) positron emission tomography (PET), compared with conventional staging by computed tomography (CT) in patients with recurrent or metastatic breast cancer. PATIENTS AND METHODS We retrospectively evaluated intrathoracic lymph nodes using FDG PET and CT data in 73 consecutive patients with recurrent or metastatic breast cancer who had both CT and FDG PET within 30 days of each other. In reviews of CT scans, mediastinal nodes measuring 1 cm or greater in the short axis were considered positive. PET was considered positive when there were one or more mediastinal foci of FDG uptake greater than the mediastinal blood pool. RESULTS Overall, 40% of patients had abnormal mediastinal or IM FDG uptake consistent with metastases, compared with 23% of patients who had suspiciously enlarged mediastinal or IM nodes by CT. Both FDG PET and CT were positive in 22%. In the subset of 33 patients with assessable follow-up by CT or biopsy, the sensitivity, specificity, and accuracy for nodal disease was 85%, 90%, and 88%, respectively, by FDG PET; 54%, 85%, and 73%, respectively, by prospective interpretation of CT; and 50%, 83%, and 70%, respectively, by blinded observer interpretation of CT. Among patients suspected of having only locoregional disease recurrence (n = 33), 10 had unsuspected mediastinal or IM disease by FDG PET. CONCLUSION FDG PET may uncover disease in these nodal regions not recognized by conventional staging methods. Future prospective studies using histopathology for confirmation are needed to validate the preliminary findings of this retrospective study.

FDG PET, PET/CT, and Breast Cancer Imaging

Currently, the clinical role of positron emission tomography (PET) and PET/computed tomography (CT) in patients with breast cancer is to provide additional information in select scenarios in which results of conventional imaging are indeterminate or of limited utility. There is currently no clinical role for fluorodeoxyglucose (FDG) PET in detection of breast cancer or evaluation of axillary lymph nodes, but these are areas of active research. FDG PET is complementary to conventional staging procedures and should not be a replacement for either bone scintigraphy or diagnostic CT. FDG PET and PET/CT have been shown to be particularly useful in the restaging of breast cancer, in evaluation of response to therapy, and as a problem-solving method when results of conventional imaging are equivocal. In these situations, FDG PET often demonstrates locoregional or unsuspected distant disease that affects management. PET has demonstrated a particular capability for evaluation of chemotherapy response in both patients with locally advanced breast carcinoma and those with metastatic disease.

Utilizing SENSE to achieve lower station sub-millimeter isotropic resolution and minimal venous enhancement in peripheral MR angiography†

To use the parallel imaging technique, sensitivity encoding (SENSE), to increase spatial resolution and decrease venous contamination in peripheral magnetic resonance angiography (MRA).

Evaluation of the internal mammary lymph nodes by FDG-PET in locally advanced breast cancer (LABC).

The presence of internal mammary (IM) lymph node metastases in breast cancer predicts outcome and may alter treatment. Standard imaging has limited usefulness for evaluation of the IM chain because of low sensitivity. Our preliminary studies suggested that [F-18]-2-fluoro-d-glucose positron emission tomography (FDG-PET) improves the detection of IM and mediastinal metastases. We therefore performed a retrospective review of women who underwent FDG-PET prior to treatment to determine the benefit of PET for imaging IM disease. The records of 28 consecutive patients undergoing FDG-PET prior to neoadjuvant chemotherapy for suspected locally advanced breast cancer (LABC) were reviewed. The presence of abnormal IM uptake on FDG-PET was noted. IM uptake on FDG PET was compared with standard radiographic imaging and was correlated with putative risk factors for IM involvement and with clinical patterns of failure. Patients did not undergo IM biopsy; however, patterns of failure were assessed to validate the FDG-PET findings. Clearly abnormal FDG uptake in the IM nodes was seen in 7 of 28 women (25%). Prospective conventional chest imaging failed to identify IM metastases in any patient. IM uptake on PET was associated with large size of the primary tumor (P = 0.03) and with inflammatory disease (P = 0.04). The presence of IM FDG uptake predicted failure by a pattern consistent with spread from IM lymph node metastasis. FDG-PET appears to be a useful noninvasive modality to detect IM metastases in LABC. Pathologic verification in a prospective study is necessary to confirm these findings.

Steady-state free precession MRA of the renal arteries: breath-hold and navigator-gated techniques vs. CE-MRA.

To explore the use of breath‐hold and navigator‐gated noncontrast Steady State Free Precession (SSFP) MR angiography (MRA) protocols for the evaluation of renal artery stenosis (RAS).

Navigator-Gated MR Angiography of the Renal Arteries: A Potential Screening Tool for Renal Artery Stenosis

OBJECTIVE The purpose of our study was to determine how well unenhanced navigator-gated steady-state free precession (Nav SSFP) MR angiography (MRA) performs as a screening test for the detection of renal artery stenosis. SUBJECTS AND METHODS Forty patients referred to rule out renal artery stenosis were imaged using an optimized Nav SSFP MRA sequence before conventional contrast-enhanced MRA (CE-MRA). Two radiologists evaluated Nav SSFP for maximum stenosis measurement, and comparison was made with CE-MRA results. RESULTS Fifteen of the 40 patients had greater than 50% renal artery stenosis as determined on CE-MRA. Sensitivity for detecting renal artery stenosis with Nav SSFP was 100%; specificity, 84%; negative predictive value, 100%; and positive predictive value, 79%. The average mean stenosis difference between Nav SSFP and CE-MRA was 10% +/- 9%. CONCLUSION Sensitivity and negative predictive value for the detection of renal artery stenosis using Nav SSFP were perfect, with an acceptable specificity of 84%. This suggests Nav SSFP is a promising technique for simple unenhanced screening for the detection of renal artery stenosis.

The prevalence and natural history of gallstones in spinal cord injured patients

BACKGROUND Individuals with a spinal cord injury are at increased risk for the development of gallstones. Because these patients cannot reliably manifest classic symptoms of biliary colic, they may be more likely to present with advanced biliary complications than patients with intact abdominal innervation. The natural history of gallstones in spinal cord injured patients has not been described. STUDY DESIGN All spinal cord injured patients seen at the Seattle Veterans Affairs Medical Center from January 1, 1993, to December 31, 1997 were included in the study. For each patient, the presence or absence of gallstones had been determined previously through screening abdominal ultrasonographic evaluations. Pertinent demographic information was obtained from medical records and patient interviews. Patients with gallstones were followed until death, cholecystectomy, or the conclusion of the study, and the annual incidence of biliary complications and patients requiring a cholecystectomy were determined. The prevalence of gallstones was established by studying the subset of patients seen at the Seattle Spinal Cord Injury Unit from January 1, 1995 to December 31, 1997. RESULTS Among the spinal cord injured patients, 31% either had gallstones or had undergone a cholecystectomy at some point after their injury. Increasing age, female gender, and greater severity of injury were risk factors for the formation of gallstones. Over the first 5 years after the diagnosis of gallstones, the annual incidence of cholecystectomy or biliary complications was 6.3% and 2.2%, respectively. CONCLUSIONS Spinal cord injured patients are at increased risk for the development of gallstones. Patients with gallstones are at an increased risk for the development of biliary complications compared with neurologically intact patients, but the magnitude of this risk does not warrant prophylactic cholecystectomy.

Preoperative evaluation of patients awaiting liver transplantation: Comparison of multiphasic contrast-enhanced 3D magnetic resonance to helical computed tomography examinations†

To determine the feasibility of using a multiphasic magnetic resonance (MR) examination to evaluate the hepatic arterial anatomy and parenchyma in patients awaiting orthotopic liver transplantation (OLT).