Fetterly, Kenneth A.

PurposeWhile scatter from the patient is assumed to be the primary source of occupational radiation dose associated with fluoroscopically guided interventional procedures, the potential contribution of scatter from the x‐ray collimator assembly is unknown. The purpose of this work was to survey clinical x‐ray angiography systems to assess the potential contribution of collimator assembly scatter on occupational radiation dose.MethodsExperimental methods were designed to measure the relative contributions of scatter originating from within the collimator assembly of the x‐ray tube to total scatter, which included scatter from a patient‐simulating phantom. Measurements were acquired as a function of lateral distance from the x‐ray beam center using a posterior anterior (PA) projection and at a fixed location for variable right anterior oblique to left anterior oblique projections in the range −90º to 90º. For one system, the collimator assembly was partially disassembled to assess the scatter contribution of individual components. For two systems, 0.5 mm Pb was added to the inner surface of the collimator assembly cover and tested for efficacy to block collimator assembly scatter.ResultsConsidering all x‐ray systems and only the PA projection, collimator assembly scatter contributed 20–50% to total scatter. For x‐ray projection angles of −90º to 90º, the relative contribution of collimator assembly to total scatter was dependent on projection angle and ranged from 5% to 56%. X‐ray systems with kerma‐area product meters demonstrated higher collimator assembly scatter than those without. Considering all projection angles, the addition of 0.5 mm Pb to the inside of the collimator assembly cover reduced collimator assembly scatter from 28% to 16% of total scatter for both systems.ConclusionFindings from this work suggest that contemporary radiation safety practices and guidelines should be revised to account for scatter originating from the collimator assembly of angiographic x‐ray tubes.

PurposeElectronic noise associated with passive pixel (PP) x‐ray angiography flat panel detectors is known to compromise fluoroscopic image quality. An active pixel (AP) crystalline silicon x‐ray detector with potential for reduced influence of electronic noise is commercially available. The purpose of this work was to compare the performance of the AP vs PP x‐ray angiography detectors over a detector target dose (DTD) range relevant for invasive cardiology procedures.MethodsA total of 16 passive pixel detector systems representing two models and two active pixel detector systems of a single model were tested. Iodine contrast (160 mg I ml−1) disk‐shaped test objects of diameter 0.5–4.0 mm were embedded in 30 × 30 cm2 25‐cm‐thick PMMA phantom. Detector target dose was 6, 18, and 120 nGy and 1204 test signal present and signal absent images were acquired. A channelized Hotelling observer statistical model (CHO) was used to estimate detectability index (d′) of the detectors for the various test objects. The CHO included correction for bias from finite sampling and that due to temporally variable electronic noise.ResultsDetectability index estimates demonstrated similar performance between the two models of PP detectors and relatively improved performance for the AP detectors for all DTD levels and test object diameters. For DTD = 120 nGy and the 4.0 mm test object, d′ of the AP detectors was 13% and 20% greater than that of the PP detectors. For DTD = 6 nGy, d′ of the AP detectors was 42% and 54% greater.ConclusionsThe AP x‐ray angiography detector demonstrated superior performance throughout the DTD range tested and especially for DTD consistent with low‐dose fluoroscopy. The improved performance of the AP detectors may facilitate reduced patient dose and/or improved image quality.

Abstract Physicians performing x-ray guided interventional procedures have a keen interest in radiation safety. Radiation dose to tissues and organs of the head and neck are of particular interest because they are not routinely protected by wearable radiation safety devices. This study was conducted to facilitate estimation of radiation dose to tissues of the head and neck of interventional physicians based on the dose recorded by a personal dosimeter worn on the left collar. Scatter beam qualities maximum energy and HVL were measured for 40 scatter beams emitting from an anthropomorphic patient phantom. Variables of the scatter beams included scatter angle (35° and 90°), primary beam peak tube potential (60, 80, 100, and 120 kVp), and 5 Cu spectral filter thicknesses (0–0.9 mm). Four reference scatter beam qualities were selected to represent the range of scatter beams realized in a typical practice. A general radiographic x-ray tube was tuned to produce scatter-equivalent radiographic beams and used to simultaneously expose the head and neck of an anthropomorphic operator phantom and radiochromic film. The geometric relationship between the x-ray source of the scatter-equivalent beams and the operator phantom was set to mimic that between a patient and physician performing an invasive cardiovascular procedure. Dose to the exterior surface of the operator phantom was measured with both 3 × 3 cm 2 pieces of film and personal dosimeters positioned at the location of the left collar. All films were scanned with a calibrated flatbed scanner, which converted the film’s reflective density to dose. Films from the transverse planes of the operator phantom provided 2D maps of the dose distribution within the phantom. These dose maps were normalized by the dose at the left collar, providing 2D percent of left collar dose (LCD) maps. The percent LCD maps were overlain with bony anatomy CT images of the operator phantom and estimates of percent LCD to the left, right and whole brain, brain stem, lenses of the eyes, and carotid arteries were calculated. Per expectation, results indicated greater percent dose to superficial versus deep tissues and increasing percent dose to deep tissues with increasing scatter-equivalent beam energy and HVL. The results enable estimation of the scatter dose to tissues of the head and neck of interventional physicians based on occupational dose measured by a personal dosimeter worn at the collar outside the protective apron.

ObjectivesThe purpose of this work is to describe methods to measure the 3D angular orientation of cardiovascular structures based on a planar image of a valvuloplasty balloon. These methods facilitate X‐ray beam alignment with respect to the anatomy of interest.BackgroundX‐ray beam projections which are perpendicular to the long axis of cardiovascular structures are required to support interventional procedures, including transcatheter aortic valve implant (TAVI).MethodsDuring the TAVI procedure, the 3D angular orientation of the LVOT of 10 patients was measured from a single planar image of an aortic valvuloplasty balloon and the continuous range of X‐ray projection angles which are aligned with the aortic valve plane were calculated (research method). Misalignment of the X‐ray beam and TAVI valve frame was measured from images of the deployed valve. The accuracy of the research method was compared to clinical standard method to determine appropriate X‐ray projection angles, which utilized CT and aortography.ResultsUsing the clinical standard method, the median misalignment of the X‐ray beam and TAVI valve frame was 8.6° (range 2.6° to 21°). Misalignment was reduced to 2.5° (range 0° to 10°) using the research method.ConclusionsThe 3D angular orientation of cardiovascular structures can be measured accurately from a single X‐ray projection image of a known cardiovascular device contained within the anatomy of interest. For TAVI procedures, improved X‐ray beam alignment may help facilitate procedural success. © 2016 Wiley Periodicals, Inc.

Abstract Channelized Hotelling model observer (CHO) methods were developed to assess performance of an x-ray angiography system. The analytical methods included correction for known bias error due to finite sampling. Detectability indices ( d ′ ) corresponding to disk-shaped objects with diameters in the range 0.5–4 mm were calculated. Application of the CHO for variable detector target dose (DTD) in the range 6–240 nGy frame −1 resulted in d ′ estimates which were as much as 2.9× greater than expected of a quantum limited system. Over-estimation of d ′ < ∼ 3.0 was presumed to be a result of bias error due to temporally variable non-stationary noise. Statistical theory which allows for independent contributions of ‘signal’ from a test object (o) and temporally variable non-stationary noise (ns) was developed. The theory demonstrates that the biased d β ′ is the sum of the detectability indices associated with the test object ( d o ′ ) and non-stationary noise ( d ns ′ ). Given the nature of the imaging system and the experimental methods, d o ′ cannot be directly determined independent of d ns ′ . However, methods to estimate d ns ′ independent of d o ′ were developed. In accordance with the theory, d ns ′ was subtracted from experimental estimates of d β ′ , providing an unbiased estimate of d o ′ . Estimates of d o ′ exhibited trends consistent with expectations of an angiography system that is quantum limited for high DTD and compromised by detector electronic readout noise for low DTD conditions. Results suggest that these methods provide d o ′ estimates which are accurate and precise for d o ′ ⩾ ∼ 1.0 . Further, results demonstrated that the source of bias was detector electronic readout noise. In summary, this work presents theory and methods to test for the presence of bias in Hotelling model observers due to temporally variable non-stationary noise and correct this bias when the temporally variable non-stationary noise is independent and additive with respect to the test object signal.

ObjectivesTo determine the feasibility of automated co‐registration of angiography and intravascular ultrasound (IVUS) to facilitate integration of these two imaging modalities in a synchronous manner.BackgroundIVUS provides cross‐sectional imaging of coronary arteries but lacks overview of the vascular territory provided by angiography. Co‐registration of angiography and IVUS would increase utility of IVUS in the clinical setting.MethodsForty‐nine consecutive patients undergoing surveillance for cardiac allograft vasculopathy with angiography and IVUS of the left anterior descending artery (LAD) were enrolled. A pre‐IVUS angiogram of the LAD was performed followed by an ECG‐triggered fluoroscopy (ECGTF) during IVUS pullback at 0.5 mm/s using an automatic pullback device. ECGTF was used to track the IVUS catheter during pullback and establish a spatial relationship to the pre‐IVUS angiogram. Angio‐IVUS co‐registration was performed with a research prototype (Siemens Healthcare, Germany) and accuracy was evaluated by distance mismatch between angiography and IVUS images at vessel bifurcations.ResultsMedian age was 54 (44.5, 67) years. The population was 82.6% male with minimal risk factors. The median (IQR) co‐registration distance mismatch measured at 108 bifurcations in 42 (85%) patients was 0.35 (0.00–1.16) mm. Seven patients were excluded due to inappropriate data acquisition (n = 3) and failure of tracking (n = 4), e.g., due to overlapping sternal wires. Estimated effective radiation dose for ECGTF was 0.09 mSv.ConclusionThis study demonstrates the feasibility of angio‐IVUS co‐registration which may be used as a clinical tool for localizing IVUS cross‐sections along an angiographic roadmap. © 2015 Wiley Periodicals, Inc.

Background— Pulmonary hypertension and right ventricular (RV) dysfunction are common in patients with advanced heart failure with preserved ejection fraction (HFpEF), yet their underlying mechanisms remain poorly understood. We sought to examine RV–pulmonary artery (PA) functional reserve responses and RV–PA coupling at rest and during β-adrenergic stimulation in subjects with earlier stage HFpEF. Methods and Results— In a prospective trial, subjects with HFpEF (n=39) and controls (n=18) underwent comprehensive invasive and noninvasive hemodynamic assessment using high fidelity micromanometer catheters, echocardiography, and expired gas analysis at rest and during dobutamine infusion. HFpEF subjects displayed similar RV structure but significantly impaired RV systolic (lower RV d P /d t max /IP and s′) and diastolic function (higher RV τ) coupled with more severe pulmonary vascular disease, manifest by higher PA pressures, higher PA resistance, and lower PA compliance compared with controls. Dobutamine infusion caused greater pulmonary vasodilation in HFpEF compared with controls, with enhanced reductions in PA resistance, greater increase in PA compliance, and a more negative slope in the PA pressure–flow relationship when compared with controls (all P <0.001). RV–PA coupling analysis revealed that dobutamine improved RV ejection in HFpEF subjects through afterload reduction alone, rather than through enhanced contractility, indicating RV systolic reserve dysfunction. Conclusions— Pulmonary hypertension in early stage HFpEF is related to partially reversible pulmonary vasoconstriction coupled with RV systolic and diastolic dysfunction, even in the absence of RV structural remodeling. Pulmonary vascular tone is more favorably responsive to β-adrenergic stimulation in HFpEF than controls, suggesting a potential role for β-agonists in the treatment of patients with HFpEF and pulmonary hypertension. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT01418248.