Improved microcalcification visualization using dual-energy digital mammography.

BACKGROUND: Dual-energy digital mammography (DEDM), involving a combination of high-energy (HE) and low-energy (LE) images, has been investigated as offering a potential improvement in microcalcification detection obscured by overlapping tissue structures. PURPOSE: To explore the possibility to improve detection of microcalcifications using the DEDM technique. MATERIAL AND METHODS: Three DEDM protocols were performed by adjusting the effective tube current time product (mAs) of LE image at the same (100%), one half (50%), and one-quarter (25%) of that used in HE image acquisition, named DEDM100%, DEDM50%, and DEDM25%, respectively. A single-energy digital mammography (SEDM) method was also used as a control. A total of 525 regions of interest (ROIs) were used to compare the performance of the DEDM to that of SEDM using free-response receiver-operating characteristic (FROC) and areas under the FROC curve (Az). RESULTS: All DEDM protocols ranked significantly higher than the SEDM method (P < 0.001). The true-positive fraction was 0.90 for an average of 0.017-0.042 false-positive per image using the DEDM100%, 0.017-0.114 using the DEDM50%, 0.021-0.148 using the DEDM25%, and 0.134-0.422 using the SEDM. The estimated Az values were 0.915-0.940, 0.867-0.935, 0.824-0.930, and 0.567-0.673, respectively. CONCLUSION: The DEDM50% protocol provided a trade-off benefit between accurate microcalcification detectability and radiation dose for any tissue density. Therefore, the DEDM50% has the potential to minimize excess radiation dose without a negative impact on image quality which could improve earlier diagnosis of breast cancer.

Feasibility study for the improvement of microcalcification visualization in different breast thicknesses and tissue components using a dual-energy approach in digital mammography.

OBJECTIVE: The purpose of this study was to improve detectability of microcalcifications using a dual-energy digital mammographic (DEDM) technique. METHODS: Slabs of uniform breast-equivalent plastic and an additional plate were used to mimic various breast thicknesses, from 3 to 7 cm, and to simulate microcalcification with diameters from 0.16 to 0.39 mm. Free-response receiver operating characteristics and area under the curves (Az) were used to evaluate the sensitivity of detecting microcalcifications using the DEDM compared with using the conventional single-energy digital mammography (SEDM). RESULTS: The mean number of false-positives per image was 0.0198 (Az = 0.956 ± 0.027) using DEDM compared with 0.292 (Az = 0.681 ± 0.235) using SEDM. A lower radiation dose could be possibly obtained for the DEDM technique with a thickness of less than 5 cm compared with the SEDM with a thickness larger than 5 cm. CONCLUSIONS: Microcalcifications could be more accurately and efficiently detected using the DEDM, which might bring reliable and promising applications on early computer-aided diagnosis of breast cancer.

Effects of long-term practice and task complexity on brain activities when performing abacus-based mental calculations: a PET study.

PURPOSE: The aim of this study was to examine the neural bases for the exceptional mental calculation ability possessed by Chinese abacus experts through PET imaging. METHODS: We compared the different regional cerebral blood flow (rCBF) patterns using (15)O-water PET in 10 abacus experts and 12 non-experts while they were performing each of the following three tasks: covert reading, simple addition, and complex contiguous addition. All data collected were analyzed using SPM2 and MNI templates. RESULTS: For non-experts during the tasks of simple addition, the observed activation of brain regions were associated with coordination of language (inferior frontal network) and visuospatial processing (left parietal/frontal network). Similar activation patterns but with a larger visuospatial processing involvement were observed during complex contiguous addition tasks, suggesting the recruitment of more visuospatial memory for solving the complex problems. For abacus experts, however, the brain activation patterns showed slight differences when they were performing simple and complex addition tasks, both of which involve visuospatial processing (bilateral parietal/frontal network). These findings supported the notion that the experts were completing all the calculation process on a virtual mental abacus and relying on this same computational strategy in both simple and complex tasks, which required almost no increasing brain workload for solving the latter. CONCLUSION: In conclusion, after intensive training and practice, the neural pathways in an abacus expert have been connected more effectively for performing the number encoding and retrieval that are required in abacus tasks, resulting in exceptional mental computational ability.

Total marrow irradiation with helical tomotherapy for bone marrow transplantation of multiple myeloma: first experience in Asia.

Three Asian patients with plasma cell myeloma stage IIIa with IgG predominant were selected for autologous hematopoietic cell transplantation (HSCT). Total marrow irradiation (TMI) tomotherapy planned with melphalan 140 mg/m2 as a preconditioning regimen of HSCT. Two image sets of computed tomography (CT) were scanned with 2.5 mm and 5 mm for the upper and lower part of the plan, respectively. The junction was determined and marked at 15 cm above knee on both thighs for upper and lower part of the plan. The clinical target volume (CTV) included the entire skeletal system. The planning target volume (PTV) was generated with with 0.8 cm for CTV(extremities) and with 0.5 cm margin for all other bones of CTV. A total dose of 800 cGy (200 cGy/fraction) was delivered to the PTV. Update to presentation, all of three patients post transplant without evidence of active disease were noted. During TMI treatment, one with grade 1 vomiting, two with grade 1 nausea, one with grade 1 mucositis, and three with grade 1 anorexia were noted. Toxicity of treatment was scored according to the Common Terminology Criteria for Adverse Events v3.0 (CTCAE v3.0). The average for upper part versus lower part of PTV (Bone marrow) of CI and H-index were 1.5 and 1.4 versus 1.2 and 1.2, respectively. The dose reduction of TMI tomotherapy to various OARs of head, chest, and abdomen relative to TBI varied from 31% to 74%, 21% to 51%, and 46% to 63%, respectively. The maximum average value of registration for upper torso versus lower extremities in different translation directions were 5.1 mm versus 4.1 mm for pretreatment and 1.5 mm versus 0.7 mm for post-treatment, respectively. The average treatment time for the upper versus lower part in beam-on time, setup time, and MVCT registration time took roughly 49.9, 23.3, and 11.7 min versus 11.5, 10.0, and 7.3 min, respectively. The margin of PTV could be less than 1 cm under good fixation and close position confirmation with MVCT. Antiemetics should be prescribed in the whole course of TMI for emesis prevention. TMI technique replaced TBI technique with 8 Gy as conditioning regiment for multiple myeloma could be acceptable for the Asian and the outcomes were feasible for the Asian.

Integration of SimSET photon history generator in GATE for efficient Monte Carlo simulations of pinhole SPECT.

The authors developed and validated an efficient Monte Carlo simulation (MCS) workflow to facilitate small animal pinhole SPECT imaging research. This workflow seamlessly integrates two existing MCS tools: simulation system for emission tomography (SimSET) and GEANT4 application for emission tomography (GATE). Specifically, we retained the strength of GATE in describing complex collimator/detector configurations to meet the anticipated needs for studying advanced pinhole collimation (e.g., multipinhole) geometry, while inserting the fast SimSET photon history generator (PHG) to circumvent the relatively slow GEANT4 MCS code used by GATE in simulating photon interactions inside voxelized phantoms. For validation, data generated from this new SimSET-GATE workflow were compared with those from GATE-only simulations as well as experimental measurements obtained using a commercial small animal pinhole SPECT system. Our results showed excellent agreement (e.g., in system point response functions and energy spectra) between SimSET-GATE and GATE-only simulations, and, more importantly, a significant computational speedup (up to approximately 10-fold) provided by the new workflow. Satisfactory agreement between MCS results and experimental data were also observed. In conclusion, the authors have successfully integrated SimSET photon history generator in GATE for fast and realistic pinhole SPECT simulations, which can facilitate research in, for example, the development and application of quantitative pinhole and multipinhole SPECT for small animal imaging. This integrated simulation tool can also be adapted for studying other preclinical and clinical SPECT techniques.

Merging molecular and anatomical information: a feasibility study on rodents using microPET and MRI.

OBJECTIVE: The use of the micro positron emission tomography (microPET) technique provides a powerful means for molecular imaging on small animals, while its inferior spatial resolution offers insufficient anatomical information which impedes the interpretations of the scans. To improve this limitation, it often relies on a clinical magnetic resonance imaging (MRI) for providing anatomical details. In this study, we designed and developed a new image co-registration platform which contains a stereotactic frame and external fiducial markers for microPET and MRI studies. The image co-registration accuracies were also validated by this new platform using various imaging protocols for microPET and MRI. METHODS: The microPET images were reconstructed by filtered back-projection (FBP) and ordered subset expectation maximization (OSEM) methods. Two MRI pulse sequences, two-dimensional T1-weighted fast spin-echo (FSE) and three-dimensional spoiled gradient recalled (SPGR), were employed in the studies. Two MRI scanning protocols were proposed for small animal imaging: the whole-body high-speed mode and the partial high-resolution mode. RESULTS: Reconstructed images from two different modalities were integrated by point-to-point registration via the external fiducials. Four inter-modality matched co-registration pairs (FBP-FSE, FBP-SPGR, OSEM-FSE, OSEM-SPGR) were obtained for both the high speed and high resolution modes. Co-registration accuracy was given as the average fiducial registration error (FRE) between the centroids of six markers from the registered images. The overall systemic FREs were about 0.50 mm. CONCLUSIONS: From the inter-modality FRE comparison, MRI imaging with FSE performed better than that with SPGR sequence, due to its higher signal-to-noise ratio and less magnetic susceptibility effects. In the microPET perspective, the OSEM was superior to the FBP, as a result of fewer image artifacts.

Clinical feasibility of Gd-EOB-DTPA-enhanced MR imaging for assessing liver function: validation with ICG tests and parenchymal cell volume.

OBJECTIVE: Using Gd-EOB-DTPA-enhanced MRI to assess liver function and validate with indocyanine green (ICG) tests and parenchymal cell volume (PCV). METHODS: Nineteen patients scheduled for operation were enrolled. Functional liver volume (FLV) was computed from 20min post-contrast images. ICG retention was measured in serum 15min after injection. The histological PCV was determined from resected liver specimen. RESULTS: FLV showed significantly correlated with ICG retention (ICG-R15: r=-0.47, P=.042) and PCV (r=0.814, P<.001). CONCLUSIONS: Gd-EOB-DTPA-enhanced MRI is clinically feasible for quantifying liver function.

A positron emission tomography/computed tomography (PET/CT) acquisition protocol for CT radiation dose optimization.

BACKGROUND: In current combined positron emission tomography/computed tomography (PET/CT) systems, high-quality CT images not only increase diagnostic value by providing anatomic delineation of hyper- and hypometabolic tissues, but also shorten the acquisition time for attenuation correction compared with standard PET imaging. However, this technique potentially introduces more radiation burden to patients as a result of the higher radiation exposure from CT. METHODS: In this study, the radiation doses delivered from typical germanium-based and CT-based transmission scans were measured and compared using an anthropomorphic Rando Alderson phantom with insertions of thermoluminescent dosimeters. Image geometric distortion and quantified uptake values in PET images with different manipulating CT acquisition protocols for attenuation correction were also evaluated. RESULTS: It was found that radiation doses during germanium-based transmission scans were almost negligible, while doses from CT-based transmission scans were significantly higher. Using a lower radiation dose, the CT acquisition protocol did not significantly affect attenuation correction and anatomic delineation in PET. CONCLUSIONS: This study revealed the relation between image information and dose. The current PET/CT imaging acquisition protocol was improved by decreasing the radiation risks without sacrificing the diagnostic values.

Monte Carlo simulation of a GE eXplore VISTA system for quantitative small animal PET imaging.

OBJECTIVE: We aim to establish an evaluation platform for the GE eXplore VISTA small animal positron emission tomography (PET) scanner, a dual layer phoswich system, by using Monte Carlo simulation. METHODS: We developed a detection model based on the Geant4 Application for Tomographic Emission to realistically reproduce the physics of PET, the scanner configuration, and the data collecting system of an eXplore VISTA system. For verification purpose, several different physical phantoms were simulated to perform evaluation tests, including sensitivity, spatial resolution, scatter fraction, and count rate performance, which were compared with an actual scanner. After the experimental validation, our detection model was applied to assess the quantification loss in the reconstructed images associated with photon attenuation, photon scatter, and random coincidences. RESULTS: A simulated sensitivity profile as a function of 18F point source axial position was fitted to the measured results. In terms of spatial resolution, agreement was within 10-18% for the point source at various locations. The simulated and measured scatter fractions differed by less than 4.3 and 5.2% for the physical mouse and rat phantoms, respectively. The count rate performance of our model was matched by the measured results, up to the peak activity concentration of 455 kBq/ml for the mouse-sized phantom and 141 kBq/ml for the rat-sized phantom. Finally, we found that photon attenuation is the dominant physical degrading factor in quantitative analysis (> 13.4%). CONCLUSION: These results suggested that the proposed detection model is able to produce realistic data from the eXplore VISTA system with knowing the ground truth, thus facilitating its evaluation for small animal PET studies.

Toward quantitative small animal pinhole SPECT: assessment of quantitation accuracy prior to image compensations.

PURPOSE: We assessed the quantitation accuracy of small animal pinhole single photon emission computed tomography (SPECT) under the current preclinical settings, where image compensations are not routinely applied. PROCEDURES: The effects of several common image-degrading factors and imaging parameters on quantitation accuracy were evaluated using Monte-Carlo simulation methods. Typical preclinical imaging configurations were modeled, and quantitative analyses were performed based on image reconstructions without compensating for attenuation, scatter, and limited system resolution. RESULTS: Using mouse-sized phantom studies as examples, attenuation effects alone degraded quantitation accuracy by up to -18% (Tc-99m or In-111) or -41% (I-125). The inclusion of scatter effects changed the above numbers to -12% (Tc-99m or In-111) and -21% (I-125), respectively, indicating the significance of scatter in quantitative I-125 imaging. Region-of-interest (ROI) definitions have greater impacts on regional quantitation accuracy for small sphere sources as compared to attenuation and scatter effects. For the same ROI, SPECT acquisitions using pinhole apertures of different sizes could significantly affect the outcome, whereas the use of different radii-of-rotation yielded negligible differences in quantitation accuracy for the imaging configurations simulated. CONCLUSIONS: We have systematically quantified the influence of several factors affecting the quantitation accuracy of small animal pinhole SPECT. In order to consistently achieve accurate quantitation within 5% of the truth, comprehensive image compensation methods are needed.

An imaging co-registration system using novel non-invasive and non-radioactive external markers.

We present a system of image co-registration and its validation in phantom and volunteer studies. The system co-registered images via six novel non-invasive and non-radioactive external markers. The fiducial markers were attached with sponge bases on the skin surface of the phantom and the volunteers in a non-collinear and non-coplanar array. The subjects were scanned with a 1.5-T magnetic resonance (MR) imager using 2D spin-echo T1-weighted (SE) and 3D spoiled gradient recalled pulse sequences (SPGR) and with a positron emission tomography (PET) scanner for transmission imaging (TI) and emission imaging (EI). The sponge bases created radiolucent gaps with good contrast between the fiducial markers and skin surface. They made the markers visible with clear edge boundaries on both PET and MR images. The images to be registered were rescaled, interpolated, reformatted and followed by point-to-point registration for coordinate determination and the estimation of geometrical transformation and fiducial registration errors (FREs) via the fiducial markers. The images formed four matched pairs of inter-modality (SE-TI, SPGR-TI, SE-EI and SPGR-EI) and two pairs of intra-modality (SE-SPGR, TI-EI) imaging for direct co-registration. The parameters for direct co-registration of SE-TI and SPRG-TI were subsequently used as a bridge and applied for indirect co-registration of SE with EI (SE-EI(TI)) and SPGR with EI (SPGR-EI(TI)), respectively. The overall FREs of the phantom were, respectively, 1.50 mm for inter-modality and 1.10 mm for intra-modality direct co-registration. Those of volunteers were, respectively, 1.79 mm for inter-modality and 1.21 mm for intra-modality direct co-registration. For indirect co-registration, the overall FREs of the phantom were 2.53 mm (SE-EI(TI)) and 2.28 (SPGR-EI(TI)) mm; those of volunteers were 2.84 mm (SE-EI(TI)) and 2.81 mm (SPGR-EI(TI)). The errors of direct co-registration were smaller than those of indirect co-registration; the errors of phantom studies, MR-EI and SPGR-PET were smaller than those of the volunteer studies, MR-TI and SE-PET, respectively (all P<0.01, paired-difference test). In conclusion, motion artefacts, imaging blurring and spatial resolution of imaging remained the key factors affecting the accuracy of co-registration. High-accuracy indirect co-registration is provided by using non-invasive and non-radioactive external fiducial markers. The errors were less than 3 mm for both phantom and volunteer studies. The system is applicable for imaging co-registration of inter-modality non-dual imaging, inter-modality multi-tracer imaging and intra-modality multiple parameter images in clinical practice.

Radiation exposure during transmission measurements: comparison between CT- and germanium-based techniques with a current PET scanner.

In positron emission tomographic (PET) scanning, transmission measurements for attenuation correction are commonly performed by using external germanium-68 rod sources. Recently, combined PET and computed tomographic (CT) scanners have been developed in which the CT data can be used for both anatomical-metabolic image formation and attenuation correction of the PET data. The purpose of this study was to evaluate the difference between germanium- and CT-based transmission scanning in terms of their radiation doses by using the same measurement technique and to compare the doses that patients receive during brain, cardiac and whole-body scans. Measurement of absorbed doses to organs was conducted by using a Rando Alderson phantom with thermoluminescent dosimeters. Effective doses were calculated according to the guidelines in the International Commission on Radiation Protection Publication Number 60. Compared with radionuclide doses used in routine 2-[fluorine-18]-fluoro-2-deoxy-D-glucose PET imaging, doses absorbed during germanium-based transmission scans were almost negligible. On the other hand, absorbed doses from CT-based transmission scans were significantly higher, particularly with a whole-body scanning protocol. Effective doses were 8.81 mSv in the high-speed mode and 18.97 mSv in the high-quality mode for whole-body CT-based transmission scans. These measurements revealed that the doses received by a patient during CT-based transmission scanning are more than those received in a typical PET examination. Therefore, the radiation doses represent a limitation to the generalised use of CT-based transmission measurements with current PET/CT scanner systems.