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Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications

Thu, 07/14/2016 - 8:58pm

PURPOSE: High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facilitate simultaneous acquisition of precontrast and postcontrast images for subtraction angiography without pixel registration artifacts and can facilitate high-resolution real-time imaging during image-guided interventions. Hence, this study was conducted to determine the spatial resolution characteristics of a hexagonal pixel array photon-counting cadmium telluride (CdTe) detector.

METHODS: A 650 mum thick CdTe Schottky photon-counting detector capable of concurrently acquiring up to two energy-windowed images was operated in a single energy-window mode to include photons of 10 keV or higher. The detector had hexagonal pixels with apothem of 30 mum resulting in pixel pitch of 60 and 51.96 mum along the two orthogonal directions. The detector was characterized at IEC-RQA5 spectral conditions. Linear response of the detector was determined over the air kerma rate relevant to image-guided interventional procedures ranging from 1.3 nGy/frame to 91.4 muGy/frame. Presampled modulation transfer was determined using a tungsten edge test device. The edge-spread function and the finely sampled line spread function accounted for hexagonal sampling, from which the presampled modulation transfer function (MTF) was determined. Since detectors with hexagonal pixels require resampling to square pixels for distortion-free display, the optimal square pixel size was determined by minimizing the root-mean-squared-error of the aperture functions for the square and hexagonal pixels up to the Nyquist limit.

RESULTS: At Nyquist frequencies of 8.33 and 9.62 cycles/mm along the apothem and orthogonal to the apothem directions, the modulation factors were 0.397 and 0.228, respectively. For the corresponding axis, the limiting resolution defined as 10% MTF occurred at 13.3 and 12 cycles/mm, respectively. Evaluation of the aperture functions yielded an optimal square pixel size of 54 mum. After resampling to 54 mum square pixels using trilinear interpolation, the presampled MTF at Nyquist frequency of 9.26 cycles/mm was 0.29 and 0.24 along the orthogonal directions and the limiting resolution (10% MTF) occurred at approximately 12 cycles/mm. Visual analysis of a bar pattern image showed the ability to resolve close to 12 line-pairs/mm and qualitative evaluation of a neurovascular nitinol-stent showed the ability to visualize its struts at clinically relevant conditions.

CONCLUSIONS: Hexagonal pixel array photon-counting CdTe detector provides high spatial resolution in single-photon counting mode. After resampling to optimal square pixel size for distortion-free display, the spatial resolution is preserved. The dual-energy capabilities of the detector could allow for artifact-free subtraction angiography and basis material decomposition. The proposed high-resolution photon-counting detector with energy-resolving capability can be of importance for several image-guided interventional procedures as well as for pediatric applications.

Improved frame-based estimation of head motion in PET brain imaging

Thu, 07/14/2016 - 8:58pm

PURPOSE: Head motion during PET brain imaging can cause significant degradation of image quality. Several authors have proposed ways to compensate for PET brain motion to restore image quality and improve quantitation. Head restraints can reduce movement but are unreliable; thus the need for alternative strategies such as data-driven motion estimation or external motion tracking. Herein, the authors present a data-driven motion estimation method using a preprocessing technique that allows the usage of very short duration frames, thus reducing the intraframe motion problem commonly observed in the multiple frame acquisition method.

METHODS: The list mode data for PET acquisition is uniformly divided into 5-s frames and images are reconstructed without attenuation correction. Interframe motion is estimated using a 3D multiresolution registration algorithm and subsequently compensated for. For this study, the authors used 8 PET brain studies that used F-18 FDG as the tracer and contained minor or no initial motion. After reconstruction and prior to motion estimation, known motion was introduced to each frame to simulate head motion during a PET acquisition. To investigate the trade-off in motion estimation and compensation with respect to frames of different length, the authors summed 5-s frames accordingly to produce 10 and 60 s frames. Summed images generated from the motion-compensated reconstructed frames were then compared to the original PET image reconstruction without motion compensation.

RESULTS: The authors found that our method is able to compensate for both gradual and step-like motions using frame times as short as 5 s with a spatial accuracy of 0.2 mm on average. Complex volunteer motion involving all six degrees of freedom was estimated with lower accuracy (0.3 mm on average) than the other types investigated. Preprocessing of 5-s images was necessary for successful image registration. Since their method utilizes nonattenuation corrected frames, it is not susceptible to motion introduced between CT and PET acquisitions.

CONCLUSIONS: The authors have shown that they can estimate motion for frames with time intervals as short as 5 s using nonattenuation corrected reconstructed FDG PET brain images. Intraframe motion in 60-s frames causes degradation of accuracy to about 2 mm based on the motion type.

Evaluation of oxygen sensitivity of hyperpolarized helium imaging for the detection of pulmonary ischemia

Thu, 07/14/2016 - 8:58pm

PURPOSE: In this study, a new model of pulmonary embolism in rats was developed and tested, to examine if hyperpolarized (HP) (3) He MR images can measure impairment of the exchange of oxygen from the airspaces to the blood during pulmonary embolism.

METHODS: HP (3) He MRI was used to image six treatment-group rats in which a branch of the pulmonary artery was embolized, and six control-group rats. HP (3) He MR images were used to calculate the initial partial pressure of oxygen (pO ) and the rate of oxygen depletion (R) in rat lungs.

RESULTS: The pO was significantly higher in the ischemic lung than in the contralateral normal side, and pO was significantly higher in the ischemic lung than in both sides of the control lungs. Mean R in ischemic lungs was significantly lower than in the contralateral lungs, and mean R in ischemic lungs was also significantly lower than in both control lungs.

CONCLUSION: These results demonstrate that pO and R, as measured by the T1 decay of HP (3) He, are sensitive to pulmonary ischemia in rats, confirming the findings in studies performed in large animal models of pulmonary ischemia.

A Private Investigation: Radiologic-Pathologic Correlation of Testicular Tumors

Thu, 07/14/2016 - 8:58pm

To review the classification of testicular tumors, describe the sonographic and pathologic features of each tumor type, and discuss the mimics, diagnostic pitfalls, and management of testicular tumors. Method consists of pictorial review. We review sonographic and pathologic findings of several testicular tumors and tumorlike entities. Although ultrasound is the first-line imaging modality to differentiate between intratesticular and extratesticular location of an intrascrotal mass, it is not specific for intratesticular lesion characterization. Therefore, correlation with histology sampling is often necessary.

Improving the Transcription of Patient Information From Image Requisitions to the Radiology Information System

Thu, 07/14/2016 - 8:58pm

PURPOSE: The purpose of this study was to improve the transcription of patient information from imaging study requisitions to the radiology information database at a single institution.

METHODS: Five hundred radiology reports from adult outpatient radiographic examinations were chosen randomly from the radiology information system (RIS) and categorized according to their degree of concordance with their corresponding clinical order indications. The number and types of grammatical errors and types of order forms were also recorded. Countermeasures centered on the education of the technical staff and referring physician offices and the implementation of a checklist. Another sample of 500 reports was taken after the implementation of the countermeasures and compared with the baseline data using a chi2 test.

RESULTS: The number of RIS indications perfectly concordant with their corresponding clinical order indications increased from 232 (46.4%) to 314 (62.8%) after the implementation of the countermeasures (P < .0001). The number of partially concordant matches due to inadequate RIS indications dropped from 162 (32.4%) to 114 (22.8%) (P < .001), whereas the number of partially concordant matches due to inadequate clinical order indications increased from 22 (4.4%) to 57 (11.4%) (P < .0001). The number of discordant pairings dropped from 84 (16.8%) to 15 (3%) (P < .0001). Technologists began to input additional patient information obtained from the patients (not present in the image requisitions) in the RIS after the implementation of the countermeasures.

CONCLUSIONS: The education of technical staff members and the implementation of a checklist markedly improved the information provided to radiologists on image requisitions from referring providers.

MRI Findings of Injury to the Longus Colli Muscle in Patients With Neck Trauma

Thu, 07/14/2016 - 8:58pm

OBJECTIVE: The longus colli muscle (LCM) forms the bulk of the deep flexor muscles of the neck. To our knowledge, very little information on the effects of trauma on this muscle group has been published. We describe MRI findings related to injury of the LCM in patients with a history of neck trauma.

MATERIAL AND METHODS: A radiology department database was searched to identify patient medical records from 2008 to 2013 that included the keywords "longus colli" and "deep flexors." Patients with fractures and ligament injuries were excluded. Patients with other obvious large soft-tissue injuries and nontraumatic conditions were also omitted. A total of 12 patients met the inclusion criterion of having an isolated or predominant injury to the LCM. Five patients had been involved in a motor vehicle accident, and seven patients had fallen. Eleven patients had undergone a CT examination before MRI was performed.

RESULTS: No fractures were noted on CT. MRI examinations of the cervical spine were obtained for the following reasons: for increased prevertebral soft-tissue swelling noted on a CT scan plus neck pain (n = 6), for neck pain only (n = 4), or as part of a routine protocol for assessment of obtunded patients (n = 2). Eight of the 12 patients had isolated injury to the LCM. The remaining four patients also had minor injuries to the other neck muscles. The MR image showed swelling and T2 hyperintensity in the LCM and revealed free fluid in the prevertebral space.

CONCLUSION: Isolated injury to the LCM may occur in neck injuries. The MRI findings indicating such injury include increased T2 signal, swelling of the muscle, and the presence of prevertebral fluid.

Stent-assisted coil embolization of aneurysms with small parent vessels: safety and efficacy analysis

Thu, 07/14/2016 - 8:58pm

BACKGROUND: Stent-assisted coil embolization (SACE) is a viable therapeutic approach for wide-neck intracranial aneurysms. However, it can be technically challenging in small cerebral vessels ( < /=2 mm).

OBJECTIVE: To present our experience with stents approved for SACE in aneurysms with small parent arteries.

METHODS: All patients who underwent stent-assisted aneurysm treatment with either a Neuroform or an Enterprise stent device at our institution between June 2006 and October 2012 were identified. Additionally, we evaluated each patient's vascular risk factors, aneurysm characteristics (ruptured vs non-ruptured, incidental finding, recanalized) and follow-up angiography data.

RESULTS: A total of 41 patients with 44 aneurysms met our criteria, including 31 women and 10 men. Most of the aneurysms were located in the anterior circulation (75%). Stent placement in vessels 1.2-2 mm in diameter was successful in 93.2%. Thromboembolic complications occurred in 6 cases and vessel straightening was seen in 1 case only. Initial nearly complete to complete aneurysm obliteration was achieved in 88.6%. Six-month follow-up angiography showed coil compaction in three cases, one asymptomatic in-stent stenosis and stent occlusion. Twelve to 20-months' follow-up showed stable coil compaction in two patients compared with previous follow-up, and aneurysm recanalization in two patients. Twenty-four to 36-months' follow-up showed further coil compaction in one of these patients and aneurysm recanalization in a previous case of stable coil compaction on mid-term follow-up.

CONCLUSIONS: Our results suggest that SACE of aneurysms with small parent vessels is feasible in selected cases and shows good long-term patency rates of parent arteries.

Successful treatment of a giant pediatric fusiform basilar trunk aneurysm with surpass flow diverter

Thu, 07/14/2016 - 8:57pm

Fusiform aneurysms present a unique challenge to traditional microsurgical and endovascular treatment because of the lack of a discernible neck and the involvement of parent vessel. Flow diversion has increasingly become the treatment of choice for fusiform aneurysms in the anterior circulation, but its results in the posterior circulation are variable. We report successful treatment of a giant fusiform upper basilar trunk aneurysm with the Surpass flow diverter in an adolescent, and discuss the potential advantages of this emerging technology in the treatment of fusiform posterior circulation aneurysms.

Redefining Budd-Chiari syndrome: A systematic review

Thu, 07/14/2016 - 8:57pm

AIM: To re-examine whether hepatic vein thrombosis (HVT) (classical Budd-Chiari syndrome) and hepatic vena cava-Budd Chiari syndrome (HVC-BCS) are the same disorder.

METHODS: A systematic review of observational studies conducted in adult subjects with primary BCS, hepatic vein outflow tract obstruction, membranous obstruction of the inferior vena cava (IVC), obliterative hepatocavopathy, or HVT during the period of January 2000 until February 2015 was conducted using the following databases: Cochrane Library, CINAHL, MEDLINE, PubMed and Scopus.

RESULTS: Of 1299 articles identified, 26 were included in this study. Classical BCS is more common in women with a pure hepatic vein obstruction (49%-74%). HVC-BCS is more common in men with the obstruction often located in both the inferior vena cava and hepatic veins (14%-84%). Classical BCS presents with acute abdominal pain, ascites, and hepatomegaly. HVC-BCS presents with chronic abdominal pain and abdominal wall varices. Myeloproliferative neoplasms (MPN) are the most common etiology of classical BCS (16%-62%) with the JAK2V617-F mutation found in 26%-52%. In HVC-BCS, MPN are found in 4%-5%, and the JAK2V617-F mutation in 2%-5%. Classical BCS responds well to medical management alone and 1(st) line management of HVC-BCS involves percutaneous recanalization, with few managed with medical management alone.

CONCLUSION: Systematic review of recent data suggests that classical BCS and HVC-BCS may be two clinically different disorders that involve the disruption of hepatic venous outflow.

Academic-industry Collaborations in Translational Stroke Research

Thu, 07/14/2016 - 8:57pm

Academic-industry collaborations are an emerging format of translational stroke research. Next to classic contract research models, a multitude of collaboration models has been developed, some of which even allowing for multinational or intercontinental research programs. This development has recently been paralleled by first successful attempts to overcome the translational stroke research road block, such as the unprecedented success of novel endovascular approaches or the advent of the multicenter preclinical trial concept. While the first underlines the role of the industry as a major innovation driver in stroke research, the latter will require enrollment of industrial partners for optimal output. Moreover, academic-industry partnerships are invaluable to bridge the translational "valley of death" as well as funding gaps in times of dwindling public funding and declining high risk capital investments. However, these collaborations are also subject to relevant challenges because interests, values, and aims often significantly differ between cademia and industry. Here, we describe common academic-industry collaboration models as well as associated benefits and challenges in the stroke research arena. We also suggest strategies for improved planning, implementation, guidance, and utilization of academic-industry collaborations to the maximum mutual benefit.

Patient delay in seeking care for heart attack symptoms: findings from focus groups conducted in five U.S. regions

Tue, 07/12/2016 - 3:41pm

BACKGROUND: Patient delay in seeking health care for heart attack symptoms is a continuuing problem in the United States.

METHODS: Investigators conducted focus groups (N = 34; 207 participants) in major U.S. regions (NE, NW, SE, SW, MW) as formative evaluation to develop a multi-center randomized community trial (the REACT Project). Target groups included adults with previous heart attacks, those at higher risk for heart attack, and bystanders to heart attacks. There were also subgroups reflecting gender and ethnicity (African-American, Hispanic-American, White).

FINDINGS: Patients, bystanders, and those at higher risk expected heart attack symptoms to present as often portrayed in the movies, that is, as sharp, crushing chest pain rather than the more common onset of initially ambiguous but gradually increasing discomfort. Patients and those at higher risk also unrealistically judge their personal risk as low, understand little about the benefits of rapid action, are generally unaware of the benefits of using EMS/9-1-1 over alternative transport, and appear to need the "permission" of health care providers or family to act. Moreover, participants reported rarely discussing heart attack symptoms and appropriate responses in advance with health care providers, spouses, or family members. Women often described heart attack as a "male problem," an important aspect of their underestimation of personal risk. African-American participants were more likely to describe negative feelings about EMS/9-1-1, particularly whether they would be transported to their hospital of choice.

CONCLUSIONS: Interventions to reduce patient delay need to address expectations about heart attack symptoms, educate about benefits and appropriate actions, and provide legitimacy for taking specific health care-seeking actions. In addition, strategy development must emphasize the role of health care providers in legitimizing the need and importance of taking rapid action in the first place.