Peter B. Schneider

Effects of Levothyroxine on Bone Mineral Density, Muscle Force, and Bone Turnover Markers: A Cohort Study

CONTEXT Previous studies of the effects of levothyroxine (LT(4)) therapy on bone and bone metabolism have provided conflicting results. OBJECTIVE This study evaluated the potential effects and dose-response relationship of LT(4) therapy on bone mineral density (BMD) as well as bone and muscle strength. DESIGN AND SETTING We conducted a prospective, nonrandomized, controlled cohort study with 1.1 ± 0.2-yr follow-up at an academic outpatient clinic in Germany. PARTICIPANTS Ninety-seven men and premenopausal women were enrolled in the study after thyroidectomy and radioiodine remnant ablation for well-differentiated thyroid carcinoma (DTC) or strumectomy for nontoxic goiter. Patients were matched with 89 healthy controls. INTERVENTIONS Twenty-eight men and 46 women on TSH-suppressive doses of LT(4) had DTC, and 23 women were on LT(4) replacement therapy for nontoxic goiter. MAIN OUTCOME MEASURE This study assessed total and trabecular volumetric BMD (vBMD) as well as bone strength at the ultradistal radius, areal BMD at the lumbar spine and both hips, and the grip strength of the nondominant forearm. The dependent variables were annualized rates of change. RESULTS LT(4) therapy did not impair the areal BMD, bone strength, or grip strength of patients compared with controls. Women with DTC showed a significant loss of total vBMD, whereas men with DTC developed marginally less bone strength than women. Carboxy-terminal telopeptide indicated greater bone resorption in DTC patients compared with controls. CONCLUSIONS There was little evidence of adverse LT(4) effects on bone; however, premenopausal women with DTC might be at risk for reduced vBMD in their ultradistal radii.

Choosing anatomical-prior strength for MAP SPECT reconstruction to maximize lesion detectability

With the widespread availability of SPECT/CT systems it has become feasible to incorporate prior knowledge about anatomical boundaries into the SPECT reconstruction process, thus improving observer performance on tasks of clinical interest. We determine the optimal anatomical-prior strength for lesion search by measuring area under the LROC curve using human observers. We conclude that prior strength should be chosen assuming that only organ boundaries are available, even if lesion boundaries will also be known some of the time. We also test whether or not the presence of anatomical priors affects the observers strategy, and conclude that mixing images with and without priors does not hurt reader performance when priors are not available. Finally, we examine whether using an anatomical prior in SPECT reconstruction helps observer performance when the observer already knows the possible lesion location, and conclude for this task anatomical priors do not provide the same improvement seen in search tasks.

Human-observer LROC study of lesion detection in Ga-67 SPECT images reconstructed using MAP with anatomical priors

We compare the image quality of SPECT reconstruction with and without an anatomical prior. Area under the localization-response operating characteristic (LROC) curve is our figure of merit. Simulated Ga-67 citrate images, a SPECT lymph-nodule imaging agent, were generated using the MCAT digital phantom. Reconstructed images were read by human observers. Several reconstruction strategies are compared, including rescaled block iterative (RBI) and maximum-a-posteriori (MAP) with various priors. We find that MAP reconstruction using prior knowledge of organ and lesion boundaries significantly improves lesion-detection performance (p < 0.05). Pseudo-lesion boundaries, regions without increased uptake which are incorrectly treated as prior knowledge of lesion boundaries, do not decrease performance.

Impact on Reader Performance for Lesion-Detection/ Localization Tasks of Anatomical Priors in SPECT Reconstruction

With increasing availability of multimodality imaging systems, high-resolution anatomical images can be used to guide the reconstruction of emission tomography studies. By measuring reader performance on a lesion detection task, this study investigates the improvement in image-quality due to use of prior anatomical knowledge, for example organ or lesion boundaries, during SPECT reconstruction. Simulated 67Ga -citrate source and attenuation distributions were created from the mathematical cardiac-torso (MCAT) anthropomorphic digital phantom. The SIMIND Monte Carlo software was then used to generate SPECT projection data. The data were reconstructed using the De Pierro maximum a posteriori (MAP) algorithm and the rescaled-block-iterative (RBI) algorithm for comparison. We compared several degrees of prior knowledge about the anatomy: no knowledge about the anatomy; knowledge of organ boundaries; knowledge of organ and lesion boundaries; and knowledge of organ, lesion, and pseudo-lesion (non-emission uptake altering) boundaries. The MAP reconstructions used quadratic smoothing within anatomical regions, but not across any provided region boundaries. The reconstructed images were read by human observers searching for lesions in a localization receiver operating characteristic (LROC) study of the relative detection/localization accuracies of the reconstruction algorithms. Area under the LROC curve was computed for each algorithm as the comparison metric. We also had humans read images reconstructed using different prior strengths to determine the optimal trade-off between data consistency and the anatomical prior. Finally by mixing together images reconstructed with and without the prior, we tested to see if having an anatomical prior only some of the time changes the observers detection/localization accuracy on lesions where no boundary prior is available. We found that anatomical priors including organ and lesion boundaries improve observer performance on the lesion detection/localization task. Use of just organ boundaries did not provide a statistically significant improvement in performance however. We also found that optimal prior strength depends on the level of anatomical knowledge, with a broad plateau in which observer performance is near optimal. We found no evidence that having anatomical priors use lesion boundaries only when available changes the observers performance when they are not available. We conclude that use of anatomical priors with organ and lesion boundaries improves reader performance on a lesion-detection/localization task, and that pseudo-lesion boundaries do not hurt reader performance. However, we did not find evidence that a prior using only organ boundaries helps observer performance. Therefore we suggest prior strength should be tuned to the organ-only case, since a prior will likely not be available for all lesions.

An evaluation of iterative reconstruction strategies based on mediastinal lesion detection using hybrid Ga-67 SPECT images.

Using psychophysical studies, the authors have evaluated the effectiveness of various strategies for compensating for physical degradations in SPECT imaging. The particular application was Ga-67-citrate imaging of mediastinal tumors, which was chosen because Ga-67 is a particularly challenging radionuclide for imaging. The test strategies included compensations for nonuniform attenuation, distance-dependent spatial resolution, and scatter applied in various combinations as part of iterative reconstructions with the rescaled block iterative-expectation maximization (RBI-EM) algorithm. The authors also evaluated filtered backprojection reconstructions. Strategies were compared on the basis of human-observer studies of lesion localization and detection accuracy using the localization receiver operating characteristics (LROC) paradigm. These studies involved hybrid images which were obtained by adding the projections of Monte Carlo-simulated lesions to disease-free clinical projection data. The background variability in these images can provide a more realistic assessment of the relative utility of reconstruction strategies than images from anthropomorphic digital phantoms. The clinical datasets were obtained using a GE-VG dual-detector SPECT system with CT-estimated attenuation maps. After determining a target lesion contrast, they conducted pilot LROC studies to obtain a near-optimal set of reconstruction parameters for each strategy, and then conducted the strategy comparison study. The results indicate improved detection accuracy with RBI-EM as more compensations are applied within the reconstruction. The relative rankings of the test strategies agreed in most cases with those of previous studies that employed simulated projections of digital anthropomorphic phantoms, thus confirming the findings of those studies.

SPECT-CT image fusion could enhance Meckel scan

L eter to he E ditor Letter to the Editor Meckels diverticulum is the most common congenital abnormality of the gastrointestinal tract. Complications include obstruction, intussusception, perforation, diverticulitis, and gastrointestinal hemorrhage. Despite availability of modern imaging techniques, its diagnosis does not follow a proposed sequence and remains delayed. Tc pertechnetate scintigraphy can help to detect ectopic gastric mucosa in the abdomen, depending on the location and size of the ectopic tissue. The number of false negative findings could be reduced using image fusion as an appropriate technique. We report a 14-month-old girl presenting with black stools and hematochezia who had a lowered hemoglobin level of 5.6 mg/dl. Abdominal ultrasound and gastrointestinal endoscopy revealed no pathology. Contrast enhanced magnetic resonance tomography finding remained non-specific and inconclusive. Nuclear medicine was consulted to rule out or confirm a Meckels diverticulum. Detection of ectopic gastric mucosa was attempted using intravenous injection of 79 MBq Tc pertechnetate after blocking the thyroid with triiodothyronine. Sequential planar scintigraphy during 30 minutes revealed a weak and small abdominal focus after 25 minutes (one image per minute). This focus projected on the urinary bladder (Fig. 1). Single Photon Emission Computer Tomography (SPECT) imaging was acquired and co-registered with a simultaneously SPECT-CT image fusion could enhance Meckel scan

Factors Influencing Lesion Detection in SPECT Lung Images

An earlier localization ROC (LROC) study that found attenuation correction (AC) degraded the detection of solitary pulmonary nodules (SPN) in hybrid SPECT lung images had several potential shortcomings related to the simulation methods. We sought to address these issues with a revised LROC study. Clinical Tc-99m NeoTect scans acquired with a simultaneous transmission-emission protocol defined the normal cases in a single-slice LROC study. Abnormal cases contained a simulated 1-cm lung lesion. Four rescaled-block-iterative EM (RBI) reconstruction strategies applied: 1) AC, scatter correction (SC), and resolution compensation (RC); 2) AC only; 3) RC only; and 4) no corrections (NC). Images from these strategies underwent 3D Gaussian post-smoothing. Performances were defined by the average area under the LROC curve obtained from three human observers. The strategy ranking in order of decreasing performance was: 1) RBI with RC; 2) RBI with all corrections; 3) RBI with AC; and 4) RBI with no corrections. A multireader-multicase (MRMC) analysis only found significant patient and patient-strategy effects. The conflicting results concerning AC from this study and the previous one may revolve around lesion masking effects, which, by design, were not a factor in the current study.

An evaluation of iterative reconstruction strategies on mediastinal lesion detection using hybrid Ga-67 SPECT images

Hybrid LROC studies can be used to more realistically assess the impact of reconstruction strategies, compared to those constructed with digital phantoms. This is because hybrid data provides the background variability that is present in clinical imaging, as well as, control over critical imaging parameters, required to conduct meaningful tests. Hybrid data is obtained by adding Monte Carlo simulated lesions to disease free clinical projection data. Due to Ga-67 being a particularly challenging radionuclide for imaging, we use Ga- 67 hybrid SPECT data to study the effectiveness of the various correction strategies developed to account for degradations in SPECT imaging. Our data was obtained using GE-VG dual detector SPECT-CT camera. After determining a target lesion contrast we conduct pilot LROC studies to obtain a near-optimal set of reconstruction parameters for the different strategies individually. These near-optimal parameters are then used to reconstruct the final evaluation study sets. All LROC study results reported here were obtained employing human observers only. We use final LROC study results to assess the impact of attenuation compensation, scatter compensation and detector resolution compensation on data reconstructed with the RBI-EM algorithm. We also compare these with FBP reconstructions of the same dataset. Our experiment indicates an improvement in detection accuracy, as various degradations inherent in the image acquisition process are compensated for in the reconstruction process.