Faculty Bibliography

Low-dose X-ray CT is a major research area with high clinical impact. Compressed sensing using view-based sparse sampling and sparsity-promoting regularization has shown promise in simulations, but these methods can be difficult to implement on diagnostic clinical CT scanners since the X-ray beam cannot be switched on and off rapidly enough. An alternative to view-based sparse sampling is interrupted-beam sparse sampling. SparseCT is a recently-proposed interrupted-beam scheme that achieves sparse sampling by blocking a portion of the beam using a multislit collimator. The use of a multislit collimator necessitates a number of modifications to the standard compressed sensing reconstruction pipeline. In particular, we find that SparseCT reconstruction is feasible within a model-based image reconstruction framework that incorporates data fidelity weighting to consider penumbra effects and source jittering to consider the effect of partial source obstruction. Here, we present these modifications and demonstrate their application in simulations and real-world prototype scans. In simulations compared to conventional low-dose acquisitions, SparseCT is able to achieve smaller normalized root-mean square differences than tube-current reduction at larger dose reduction levels. In prototype experiments, we successfully apply our reconstruction modifications and maintain image resolution at the quarter-dose reduction level. The SparseCT design requires only small hardware modifications to current diagnostic clinical scanners, opening up new possibilities for CT dose reduction.

Objectives: To differentiate pulmonary tumor type by volumetric iodine quantification and texture analysis on dual-energy CT images.
Material(s) and Method(s): Radiology information system search for all contrast-enhanced DECT chest examinations from 1/1/2015-4/30/ 2018 was performed, filtering for those with pathology within 120 days, yielding 80 cases of pathologically-proven pulmonary lesions. 73 lesions meeting inclusion criteria were manually volumetrically segmented via open-source software using the low-kV DECT dataset. 3D-iodine quantification was achieved by mapping between high/low energy HU on a representative 2D-image, and applying to surrounding slices, with absolute iodine normalized to mid-descending aorta. Full Width Tenth Maximum was applied to each normalized iodine histogram, providing a single comprehensive measure of relative iodine concentration. Volumetric iodine values and first order texture features were assessed using Hoteling's T-squared multivariate analysis.
Result(s): 72 individuals (37 women, 35 men) with mean age 64 years were included. 44 primary, 25 metastatic, and 3 benign lesions were assessed; 22 with history of chemotherapy. Mean time between histopathologic sampling and imaging was 26 days. Mean, median and minimum volumetric iodine concentration were significant (P< 0.05) in distinguishing primary versus metastatic lesions, with P<0.01 for these measures between de novo primary and metastatic lesions. Metastatic lesions demonstrated higher mean iodine (1.2 mg/mL) in comparison to primary lesions (0.83 mg/mL). Mean and median 3D-iodine values significantly (P<0.05) differed between primary lung adenocarcinoma and squamous lesions (mean 0.95 mg/mL and 0.49 mg/mL, respectively). Skewness significantly differed between de novo versus treated primary (P=0.01), and metastatic versus primary lesions (P=0.03), and entropy between de novo primary and metastatic lesions (P<0.001), and treated versus non-treated metastases (P= 0.03).
Conclusion(s): Volumetric iodine quantification significantly differs between de novo primary versus metastatic, and primary lung adenocarcinoma versus squamous lesions. Texture features may also have a role in distinguishing tumor type and treatment response. Clinical Relevance Application: Potential role of DECT in distinguishing tumor type and treatment response

PURPOSE/OBJECTIVE:. SparseCT partially blocks the x-ray beam with a multi-slit collimator (MSC) to perform a multidimensional undersampling along the view and detector row dimensions. SparseCT undersamples the projection data within each view and moves the MSC along the z direction during gantry rotation to change the undersampling pattern. It enables reconstruction of images from undersampled data using compressed sensing algorithms. The purpose of this work is to design the spacing and width of the MSC slits and the MSC motion patterns based on beam separation, undersampling efficiency, and image quality. The development and testing of a SparseCT prototype with the designed MSC will be described in a following paper. METHODS:We chose a few initial MSC designs based on the guidance from two metrics: beam separation and undersampling efficiency. Both beam separation and undersampling efficiency were measured from numerically simulated photon distribution with MSC taken into consideration. Beam separation measures the separation between x-ray beams from consecutive slits, taking into account penumbra effects on both sides of each slit. Undersampling efficiency measures the dose-weighted similarity between penumbra undersampling and binary undersampling, in other words, the effective contribution of the incident dose to the SNR of the projection data. We then compared the initially chosen MSC designs in terms of their reconstruction image quality. SparseCT projections were simulated from fully-sampled patient projection data according to the MSC design and motion pattern, reconstructed iteratively using a sparsity-enforcing penalized weighted least squares cost function with ordered subsets/momentum algorithm, and compared visually and quantitatively. RESULTS:Simulated photon distributions indicate that the size of the penumbra is dominated by the size of the focal spot. Therefore, a wider MSC slit and a smaller focal spot lead to increased beam separation and undersampling efficiency. For 4-fold undersampling with a 1.2 mm focal spot, a minimum MSC slit width of 3 detector rows (projected to the detector surface) is needed for beam separation; for 3-fold undersampling, a minimum slit width of 4 detector rows is needed. Simulations of SparseCT projection and reconstruction indicate that the motion pattern of the MSC does not have a visible impact on image quality. An MSC slit width of 3 or 4 detector rows yields similar image quality. CONCLUSION/CONCLUSIONS:The MSC is the key component of the SparseCT method. Simulations of MSC designs incorporating x-ray beam penumbra effects showed that for 3-fold and 4-fold dose reductions, an MSC slit width of 4 detector rows provided reasonable beam separation, undersampling efficiency, and image quality.

RATIONALE AND OBJECTIVES/OBJECTIVE:This study aims to determine the optimal photon energy for image quality of the pulmonary arteries (PAs) on dual-energy computed tomography (CT) pulmonary angiography (CTPA) utilizing low volumes of iodinated contrast. MATERIALS AND METHODS/METHODS:The study received institutional review board exemption and was Health Insurance Portability and Accountability Act compliant. Adults (n = 56) who underwent dual-energy CTPA with 50-60 cc of iodinated contrast on a third-generation dual-source multidetector CT were retrospectively and consecutively identified. Twelve virtual monoenergetic kiloelectron volt (keV) image data sets (40-150 keV, 10-keV increments) were generated with a second-generation noise-reducing algorithm. Standard regions of interest were placed on main, right, left, and right interlobar pulmonary arteries; pectoralis muscle; and extrathoracic air. Attenuation [mean CT number (Hounsfield unit, HU)], noise [standard deviation (HU)], signal to noise (SNR), and contrast to noise ratio were evaluated. Three blinded chest radiologists rated (from 1 to 5, with 5 being the best) randomized monoenergetic and weighted-average images for attenuation and noise. P <.05 was considered significant. RESULTS:Region of interest mean CT number increased as keV decreased, with 40 keV having the highest value (P < .001). Mean SNR was highest for 40-60 keV (P <.05) (14.5-14.7) and was higher (P <.05) than all remaining energies (90-150 keV) for all vessel regions combined. Contrast to noise ratio was highest for 40 keV (P <.001) and decreased as keV increased. SNR was highest at 60 and 70 keV, only slightly higher than 40-50 keV (P <.05). Reader scores for 40-50 keV were greater than other energies and weighted-average images (P <.05). CONCLUSIONS:Kiloelectron volt images of 40-50 keV from the second-generation algorithm optimize attenuation on dual-energy CTPA and can potentially aid in interpretation and avoiding nondiagnostic examinations.

BACKGROUND: Dorsal midbrain syndrome (also known as Parinaud syndrome and pretectal syndrome) is a well-known complication of tumors of the pineal region. However, there are few reports regarding outcomes, especially in children. The purpose of this study was to report the ophthalmic outcomes in a group of children with pineal tumors treated at a single institution. METHODS: The medical records of pediatric patients diagnosed with pineal region tumors and evaluated at our ophthalmology clinic were studied retrospectively. Descriptive statistics were used to assess rate of dorsal midbrain syndrome, defined as one or more of the following: limitation of upgaze, pupillary light-near dissociation, and convergence retraction nystagmus. Treatment outcomes were recorded. RESULTS: A total of 35 subjects (age range, 5 months to 20 years) were included, 18 (51%) of whom were found to have dorsal midbrain syndrome. Of those 18, 16 patients (89%) had limitation of upgaze, 15 (83%) had pupillary light-near dissociation, and 9 (50%) had convergence-retraction nystagmus. Convergence insufficiency was noted in 5 patients (28%); exotropia (either intermittent or constant), in 9 (50%). Improvement in dorsal midbrain syndrome findings following treatment was seen in 7 of 17 patients (41%), but only 2 (12%) experienced complete resolution. Treatment consisted of surgery, radiation, and/or chemotherapy. CONCLUSIONS: In our study cohort of children with pineal tumors have a high incidence of dorsal midbrain syndrome. Most cases had residual findings after treatment.

PURPOSE: To determine the incidence of and factors associated with the development of mydriasis and impaired accommodation in patients with refractory or recurrent neuroblastoma receiving the anti-GD2 antibody hu14.18K322A. METHODS: The medical records of eligible patients with refractory or recurrent neuroblastoma who received escalating doses of hu14.18K322A, ranging from 2 to 70 mg/m(2)/dose for 4 consecutive days every 28 days, were retrospectively reviewed to identify ocular abnormalities arising during the treatment period. RESULTS: A total of 38 patients (median age, 7 years; 23 males) were included. All patients underwent comprehensive eye examinations prior to each course of therapy. Mydriasis was seen in 13 patients (34%), and impaired accommodation was seen in 9 (24%), indicating a dose-related effect between hu14.18K322A and both mydriasis (P = 0.021) and impaired accommodation (P = 0.029). Age and sex were not associated with ocular abnormalities. Ocular symptoms resolved in the majority of patients after the drug was discontinued. CONCLUSIONS: Side effects of mydriasis and impaired accommodation have a dose-dependent relationship with hu14.18K322A. These side effects do not warrant discontinuation of treatment, as they usually resolve after completion of therapy. Management of ocular side effects should focus on treating symptoms with manifest refraction, bifocals, or tinted spectacles.

OBJECTIVE: The maximal diameter of an abdominal aortic aneurysm (AAA) and the change in diameter over time reflect rupture risk and are used for surgical planning. However, evidence has emerged that aneurysm volume may be a better indicator of AAA remodeling. The purpose of this study was to assess the relationship between the volume and maximal diameter of the abdominal aorta in patients with untreated infrarenal AAA. MATERIALS AND METHODS: This was a retrospective study of 100 patients with infrarenal AAA who were followed for more than 6 months. We examined 2 sets of computed tomography images for each patient, acquired >/= 6 months apart. The maximal diameter and volume of the infrarenal abdominal aorta were determined by semiautomated segmentation software. RESULTS: At baseline, mean maximal infrarenal diameter was 5.1 +/- 1.0 cm and mean aortic volume was 139 +/- 72 mL. There was good correlation between the maximal diameter and aortic volume at baseline (r(2) = 0.55; P<0.001). The mean change in maximal diameter between studies was 0.2 +/- 0.3 cm and the mean volume change was 19 +/- 19 mL. However, the correlation between diameter change and volume change was modest (r(2) = 0.34; P=0.001). Most patients (n = 64) had no measurable change in maximal diameter between studies (