An 81-year-old female presented with a three year history of painless, erythematous nodules on her right proximal forearm with slow spread to the cubital fossa and distal upper arm. A 78-year-old female presented with a six month history of isolated right forearm plaque. The patient had a background medical history of inflammatory arthritis managed with oral prednisone and infliximab. In both cases calcofluor-white stain revealed organisms resembling Prototheca. Growth occurred after 72 hours on Sabouraud’s agar incubated aerobically at 30°C. The identification of Prototheca wickerhamii was confirmed using the Vitek 2 YST ID card or Vitek MS (database 3.2). Prototheca are ubiquitous environmental, achlorophyllic algae, which rarely cause infection in humans. Cutaneous infection is most commonly encountered with a slowly progressive or indolent course; however, invasive disease with significant morbidity and mortality has been reported. Most cases occur in the immunocompromised host. Treatment is always required however no consensus therapeutic guidelines exist. We present two cutaneous cases in order to highlight some of the key clinical and microbiological diagnostic features of this unusual infection.

Background: We wished to determine whether newly available flat panel detector (FPD) c-arms were (1) associated with lower radiation dose during ureteroscopy (URS) than conventional image intensifier (CII) c-arms and (2) to compare fluoroscopic image quality between the units. Materials and Methods: We retrospectively reviewed 44 consecutive patients undergoing URS at a pediatric hospital, with c-arms assigned by availability in the operating room. We performed dosimetry experiments using the same c-arms on standard phantoms. Results: Patient and case characteristics did not differ significantly between the two groups of patients. The median dose in the FPD group was less than a quarter of the dose in the CII group, 0.48 [0.42, 0.97] mGy vs 2.2 [1.1, 3.8] mGy, p < 0.0001. The FPD dose remained at less than one-third of the CII dose accounting for any difference in fluoroscopy time, and remained significant in a multivariate model including fluoroscopy time and patient weight (beta = 2.4, p = 0.007). Phantom studies showed higher image quality for FPDs at all simulated patient sizes, even at lower radiation doses. Conclusions: This is the first report comparing radiation dose from c-arms of image intensifiers and FPDs in adults or children. Use of an FPD during URS was associated with a substantially decreased absorbed dose for patients while simultaneously improving image quality.

Computed Tomography (CT) is a cornerstone of diagnostic medical imaging and provides valuable information in the care of pediatric patients. Although the potential dangers of “radiation” have obtained notoriety in the lay press, CT is a vital diagnostic tool in a wide range of clinical settings. Radiologists must be mindful of radiation safety principles, balancing the potential small risks of ionizing radiation in the care of the pediatric patient against the known benefits of performing CT studies in a variety of clinical situations. This chapter offers an updated review on the basic principles of radiation biology including stochastic (or probabilistic) effects of ionizing radiation and the linear no-threshold (LNT) model. In particular, we review the fundamentals of CT dosimetry such as CTDI, DLP and discuss methods for protocoling pediatric CTs. We also review more complex topics such as tube current, pitch, and kVp, highlight the differences between Iterative Reconstruction (IR) and Filtered backprojection, and how all these settings effect dose. We offer guidance on how to optimize image quality, while minimizing image noise and effective dose. Lastly, we offer methods to navigate the challenges of communicating and discussing radiation risk with families of our pediatric patients.

Purpose To develop a scheme to quantitatively assess localization accuracy of tomosynthesis‐guided vacuum‐assisted breast biopsy apparatus. Methods A phantom containing a metallic pellet on a flexible plastic shaft was constructed and was tested in cranio‐caudal (CC) and lateral (LAT) arm biopsy geometries following the standard clinical breast biopsy workflow. Three points were manually digitized on tomosynthesis images including: the center of the target, and the tip of the needle in pre‐ and postfire positions. The needle trajectory was determined and four error metrics were defined: (1) stroke length error (difference between the nominal and measured stroke lengths); (2) Euclidian distance between the target and center of trough (i.e., aperture); (3) longitudinal distance between target and center of trough; and (4) lateral distance between target and needle. The proposed methodology was also evaluated on a breast gel phantom and the complete biopsy procedure, including vacuum‐assisted biopsy was performed. Results Three biopsy geometries were investigated: (i) LAT arm on a prone table unit (Hologic, Affirm Prone), (ii) CC‐ and (iii) LAT arm in an upright unit (Hologic Affirm Upright). Both biopsy units passed the vendor‐provided daily localization accuracy test, with <1 mm nominal error in each dimension. The aforementioned error metrics (1) to (4) were (0.6, 1.8, 0.4, 1.7) mm, (0.4, 4.2, 4.1, 1.1) mm, and (0.3, 2.4, 0.7, 2.3) mm, respectively, for geometry‐I, ‐II, and ‐III. The gel phantom was tested on the upright unit with lateral arm and the error metrics (1) to (4) were 0.4, 2.5, 0.8, and 2.4 mm respectively. Conclusions A framework was developed to evaluate the tomosynthesis‐guided breast biopsy localization error, allowing quantitative comparisons between different systems and biopsy configurations. The proposed framework can also be extended to the stereotactic breast biopsy units. We suggest that a quantitative tolerance level for localization accuracy of breast biopsy units be established.

PURPOSE:For single-source helical Computed Tomography (CT), both Filtered-Back Projection (FBP) and statistical iterative reconstruction have been investigated. However, for dual-source CT with flying focal spot (DS-FFS CT), a statistical iterative reconstruction that accurately models the scanner geometry and acquisition physics remains unknown to researchers. Therefore, our purpose is to present a novel physics-based iterative reconstruction method for DS-FFS CT and assess its image quality.METHODS:Our algorithm uses precise physics models to reconstruct from the native cone-beam geometry and interleaved dual-source helical trajectory of a DS-FFS CT. To do so, we construct a noise physics model to represent data acquisition noise and a prior image model to represent image noise and texture. In addition, we design forward system models to compute the locations of deflected focal spots, the dimension, and sensitivity of voxels and detector units, as well as the length of intersection between x-rays and voxels. The forward system models further represent the coordinated movement between the dual sources by computing their x-ray coverage gaps and overlaps at an arbitrary helical pitch. With the above models, we reconstruct images by an advanced Consensus Equilibrium (CE) numerical method to compute the maximum a posteriori estimate to a joint optimization problem that simultaneously fits all models.RESULTS:We compared our reconstruction with Siemens ADMIRE, which is the clinical standard hybrid iterative reconstruction (IR) method for DS-FFS CT, in terms of spatial resolution, noise profile, and image artifacts through both phantoms and clinical scan datasets. Experiments show that our reconstruction has a higher spatial resolution, with a Task-Based Modulation Transfer Function (MTFtask ) consistently higher than the clinical standard hybrid IR. In addition, our reconstruction shows a reduced magnitude of image undersampling artifacts than the clinical standard.CONCLUSIONS:By modeling a precise geometry and avoiding data rebinning or interpolation, our physics-based reconstruction achieves a higher spatial resolution and fewer image artifacts with smaller magnitude than the clinical standard hybrid IR.

Purpose Inkjet printers can be used to fabricate anthropomorphic phantoms by the use of iodine-doped ink. However, challenges persist in implementing this technique. The calibration from grayscale to ink density is complex and time-consuming. The purpose of this work is to develop a printing methodology that requires a simpler calibration and is less dependent on printer characteristics to produce the desired range of x-ray attenuation values. Methods Conventional grayscale printing was substituted by single-tone printing; that is, the superposition of pure black layers of iodinated ink. Printing was performed with a consumer-grade inkjet printer using ink made of potassium-iodide (KI) dissolved in water at 1 g/ml. A calibration for the attenuation of ink was measured using a commercial x-ray system at 70 kVp. A neonate radiograph obtained at 70 kVp served as an anatomical model. The attenuation map of the neonate radiograph was processed into a series of single-tone images. Single-tone images were printed, stacked, and imaged at 70 kVp. The phantom was evaluated by comparing attenuation values between the printed phantom and the original radiograph; attenuation maps were compared using the structural similarity index measure (SSIM), while attenuation histograms were compared using the Kullback-Leibler (KL) divergence. A region of interest (ROI)-based analysis was also performed, where the attenuation distribution within given ROIs was compared between phantom and patient. The phantom sharpness was evaluated in terms of modulation transfer function (MTF) estimates and signal spread profiles of high spatial resolution features in the image. Results The printed phantom required 36 pages. The printing queue was automated and it took about 2 h to print the phantom. The radiograph of the printed phantom demonstrated a close resemblance to the original neonate radiograph. The SSIM of the phantom with respect to that of the patient was 0.53. Both patient and phantom attenuation histograms followed similar distributions, and the KL divergence between such histograms was 0.20. The ROI-based analysis showed that the largest deviations from patient attenuation values were observed at the higher and lower ends of the attenuation range. The limiting resolution of the proposed methodology was about 1 mm. Conclusion A methodology to generate a neonate phantom for 2D imaging applications, using single-tone printing, was developed. This method only requires a single-value calibration and required less than 2 h to print a complete phantom.

Purpose: Model Based Iterative Reconstruction (MBIR) is a state-of-the-art reconstruction method for multi-detector helical computed tomography (CT), and provides better image quality than other methods. Existing MBIR reconstruction methods, however, have only been implemented for single source CT, and has no implementation for more recent CT geometries, such as a dual source flying focal spot CT (DS-FFS CT), which feature a much shorter scan time and more projection samplings than single source CT. In this paper, we present the first model-based reconstruction method for DS-FFS CT and realistically models its geometry, data acquisition physics, and image spatial property. Methods: At each view angle and for each X-ray source, the geometry model imitates the X-ray focal spot and detector movement, the sensitivity of detector sensor units, and the interactions between X-rays and each voxel. We also construct a noise model to imitate projections noise and an image property model based on a generalized Markov Random Field for image denoising and maintaining a good image texture. In the end, we fuse all models together as a joint optimization problem to be solved. Results: To compare the image quality between our reconstruction and the stateof-the-art Siemens reconstruction, ADMIRE, we qualitatively and quantitatively compared spatial resolution, noise profile, CT number accuracy, and image artifacts between the two algorithms on a phantom dataset, two thoracic clinical scans, and one pediatric head scan. Experimental results show that our model-based reconstruction has a higher spatial resolution, with a Signal-Noise Ratio 1.43 times higher than ADMIRE and a Modulation Transfer Function 4 times higher than ADMIRE at spatial frequency 0.8 mm−1. In addition, both phantom and clinical datasets show fewer image artifacts in our model-based reconstruction than ADMIRE reconstructions. Conclusions: For DS-FFS CT, our model based reconstruction has a higher spatial resolution and fewer image artifacts than Siemens ADMIRE reconstruction on phantom datasets and multiple clinical applications.

Introduction: Traditionally, fluoroscopy and postoperative computed tomographic (CT) scans are used to evaluate screw position after pediatric cervical spine fusion. However, noncontained screws detected postoperatively can require revision surgery. Intraoperative O-arm is a 3-dimensional CT imaging technique, which allows intraoperative evaluation of screw position and potentially avoids reoperations because of implant malposition. This study’s objective was to evaluate the use of intraoperative O-arm in determining the accuracy of cervical implants placed by a free-hand technique using anatomic landmarks or fluoroscopic guidance in pediatric cervical spine instrumentation. Methods: A single-center retrospective study of consecutive examinations of children treated with cervical spine instrumentation and intraoperative O-arm from 2014 to 2018 was performed. In total, 44 cases (41 children, 44% men) with a mean age of 11.9 years (range, 2.1 to 23.5 y) were identified. Instability (n=16, 36%) and deformity (n=10, 23%) were the most frequent indications. Primary outcomes were screw revision rate, neurovascular complications caused by noncontained screws, and radiation exposure. Results: A total of 272 screws were inserted (60 occipital and 212 cervical screws). All screws were evaluated on fluoroscopy as appropriately placed. Four screws (1.5%) in 4 cases (9%) were noncontained on O-arm imaging and required intraoperative revision. A mean of 7.7 levels (range, 5 to 13) were scanned. The mean CT dose index and dose-length product were 15.2±6.87 mGy and 212.3±120.48 mGy×cm. Mean effective dose was 1.57±0.818 mSv. There was no association between screw location and noncontainment (P=0.129). No vertebral artery injuries, dural injuries, or neurologic deficits were related to the 4 revised screws. Conclusions: Intraoperative non-navigated O-arm is a safe and efficient method to evaluate screw position in pediatric patients undergoing cervical spine instrumentation. Noncontained screws were detected in 9% of cases (n=4). O-arm delivers low radiation doses, allows for intraoperative screw revision, and negates the need for postoperative CT scans after confirmation of optimal implant position. Level of Evidence: Level IV.

Purpose To evaluate the efficacy of convolutional neural networks (CNNs) to improve the image quality of low-dose pediatric abdominal CT images. Materials and Methods Images from 11 pediatric abdominal CT examinations acquired between June and July 2018 were reconstructed with filtered back projection (FBP) and an iterative reconstruction (IR) algorithm. A residual CNN was trained using the FBP image as the input and the difference between FBP and IR as the target such that the network was able to predict the residual image and simulate the IR. CNN-based postprocessing was applied to 20 low-dose pediatric image datasets acquired between December 2016 and December 2017 on a scanner limited to reconstructing FBP images. The FBP and CNN images were evaluated based on objective image noise and subjective image review by two pediatric radiologists. For each of five features, readers rated images on a five-point Likert scale and also indicated their preferred series. Readers also indicated their "overall preference" for CNN versus FBP. Preference and Likert scores were analyzed for individual and combined readers. Interreader agreement was assessed. Results The CT number remained unchanged between FBP and CNN images. Image noise was reduced by 31% for CNN images (P < .001). CNN was preferred for overall image quality for individual and combined readers. For combined Likert scores, at least one of the two score types (Likert or binary preference) indicated a significant favoring of CNN over FBP for low contrast, image noise, artifacts, and high contrast, whereas the reverse was true for spatial resolution. Conclusion FBP images can be improved in image space by a well-trained CNN, which may afford a reduction in dose or improvement in image quality on scanners limited to FBP reconstruction.© RSNA, 2019.

Beginning with the advent of digital radiography systems in 1981, manufacturers of these systems provided indicators of detector exposure. These indicators were manufacturer-specific, and users in facilities with equipment from multiple manufacturers found it a challenge to monitor and manage variations in indicated exposure in routine clinical use. In 2008, a common definition of exposure index (EI) was realized in International Electrotechnical Commission (IEC) International Standard 62494-1 Ed. 1, which also introduced and defined the deviation index (DI), a number quantifying the difference between the detector EI for a given radiograph and the target exposure index (EIT ). An exposure index that differed by a constant from that established by the IEC and the concept of the deviation index also appear in American Association of Physicists in Medicine (AAPM) Report No. 116 published in 2009. The AAPM Report No. 116 went beyond the IEC standard in supplying a table (Table II in the report of TG-116) titled "Exposure Indicator DI Control Limits for Clinical Images," which listed suggested DI ranges and actions to be considered for each range. As the IEC EI was implemented and clinical DI data were gathered, concerns were voiced that the DI control limits published in the report of TG-116 were too strict and did not accurately reflect clinical practice. The charge of task group 232 (TG-232) and the objective of this final report was to investigate the current state of the practice for CR/DR Exposure and Deviation Indices based on AAPM TG 116 and IEC-62494, for the purpose of establishing achievable goals (reference levels) and action levels in digital radiography. Data corresponding to EI and DI were collected from a range of practice settings for a number of body parts and views (adults and pediatric radiographs) and analyzed in aggregate and separately. A subset of radiographs was also evaluated by radiologists based on criteria adapted from the European Guidelines on Quality Criteria for Diagnostic Radiographic Images from the European Commission. Analysis revealed that typical DI distribution was characterized by a standard deviation (SD) of 1.3-3.6 with mean DI values substantially different from 0.0, and less than 50% of DI values fell within the significant action limits proposed by AAPM TG-116 (-1.0 ≤ DI ≤ 1.0). Recommendations stemming from this analysis include targeting a mean DI value of 0.0 and action limits at ±1 and ±2 SD of the DI based on actual DI data of an individual site. EIT values, DI values, and associated action limits should be reviewed on an ongoing basis and optimization of DI values should be a process of continuous quality improvement with a goal of reducing practice variation.

Background Fluoroscopy is commonly used during pediatric ureteroscopy (PURS) for urolithiasis, and the most important contributor to overall radiation exposure is fluoroscopy time (FT). One factor that may impact FT is who controls activation of the fluoroscope: the urologist (with a foot pedal) or the radiation technologist (as directed by the urologist). While there are plausible reasons to believe that either approach may lead to reduced FT, there are no systematic investigations of this question. We sought to compare FT with surgeon-control versus technologist control during PURS for urolithiasis. Methods We conducted a randomized controlled trial (Clinicaltrials.gov ID number: NCT02224287). Institutional Review Board approval was sought and obtained for this study. All subjects (or their legal guardians) provided informed consent. Each patient (age 5-26 years) was randomized to surgeon- or technologist-controlled fluoroscope activation. Block randomization was stratified by the surgeon. For technologist control, the surgeon verbally directed the technologist to activate the fluoroscope. For surgeon control, a foot pedal was used by the surgeon. The technologist controlled carm positioning, settings, and movement. The primary outcome was total FT for the procedure. Secondary outcomes included radiation exposure (entrance surface air kerma [ESAK] mGy). We also analyzed clinical and procedural predictors of FT and exposure. Mixed linear models accounting for clustering by surgeon were developed. Results Seventy-three procedures (5 surgeons) were included. The number of procedures per surgeon ranged from seven to 36. Forty-three percent were pre-stented. Thirty-one procedures were left side, 35 were right side, and seven were bilateral. Stones were treated in 71% of procedures (21% laser, 14% basket, and 65% laser/basket). Stone locations were distal ureter (11.5%), proximal/mid-ureter (8%), renal (69%), and ureteral/renal (11.5%). An access sheath was used in 77%. Median stone size was 8.0 mm (range 2.0-20.0). Median FT in the surgeon control group was 0.5 min (range 0.01-6.10) versus 0.55 min (range 0.10-5.50) in the technologist-control group (p = 0.284). Median ESAK in the surgeon control group was 46.02 mGy (range 5.44-3236.80) versus 46.99 mGy (range: 0.17-1039.31) in the technologist-control group (p = 0.362). Other factors associated with lower FT on univariate analysis included female sex (p = 0.015), no prior urologic surgeries (p = 0.041), shorter surgery (p = 0.011), and no access sheath (p = 0.006). On multivariable analysis only female sex (p = 0.017) and no access sheath (p = 0.049) remained significant. There was significant variation among surgeons (p < 0.0001); individual surgeon median FT ranged from 0.40 to 2.95 min. Conclusions Fluoroscopy time and radiation exposure are similar whether the surgeon or technologist controls fluoroscope activation. Other strategies to reduce exposure might focus on surgeon-specific factors, given the significant variation between surgeons.

In the context of health care, risk assessment is the identification, evaluation and estimation of risk related to a particular clinical situation or intervention compared to accepted medical practice standards. The goal of risk assessment is to determine an acceptable level of risk for a given clinical treatment or intervention in association with the provided clinical circumstances for a patient or group of patients. In spite of the inherent challenges related to risk assessment in pediatric cross-sectional imaging, the potential risks of ionizing radiation and sedation/anesthesia in the pediatric population are thought to be quite small. Nevertheless both issues continue to be topics of discussion concerning risk and generate significant anxiety and concern for patients, parents and practicing pediatricians. Recent advances in CT technology allow for more rapid imaging with substantially lower radiation exposures, obviating the need for anesthesia for many indications and potentially mitigating concerns related to radiation exposure. In this review, we compare and contrast the potential risks of CT without anesthesia against the potential risks of MRI with anesthesia, and discuss the implications of this analysis on exam selection, providing specific examples related to neuroblastoma surveillance imaging.