Radiation dose in cardiac imaging: how should it affect clinical decisions?

OBJECTIVE: The purpose of this article is to discuss whether and how the risks of exposure to ionizing radiation should affect clinical decision making in patients with known or suspected cardiovascular disease. CONCLUSION: Although the prevalence of cardiovascular disease and frequency of diagnostic testing has risen dramatically, cardiovascular mortality has declined. Earlier and more accurate detection of cardiovascular disease may play an important role. Concerns regarding excessive radiation exposure from cardiovascular imaging have been raised. Efforts to reduce exposure have included selection of appropriate patients for cardiovascular testing, technologic advances, educational resources, and a directed patient-centered approach to testing.

Central hyperadrenergic state after lightning strike.

OBJECTIVE: To describe and review autonomic complications of lightning strike. METHODS: Case report and laboratory data including autonomic function tests in a subject who was struck by lightning. RESULTS: A 24-year-old man was struck by lightning. Following that, he developed dysautonomia, with persistent inappropriate sinus tachycardia and autonomic storms, as well as posttraumatic stress disorder (PTSD) and functional neurologic problems. INTERPRETATION: The combination of persistent sinus tachycardia and episodic exacerbations associated with hypertension, diaphoresis, and agitation was highly suggestive of a central hyperadrenergic state with superimposed autonomic storms. Whether the additional PTSD and functional neurologic deficits were due to a direct effect of the lightning strike on the central nervous system or a secondary response is open to speculation.

A strategy to decrease partial scan reconstruction artifacts in myocardial perfusion CT: phantom and in vivo evaluation.

PURPOSE: Partial scan reconstruction (PSR) artifacts are present in myocardial perfusion imaging using dynamic multidetector computed tomography (MDCT). PSR artifacts appear as temporal CT number variations due to inconsistencies in the angular data range used to reconstruct images and compromise the quantitative value of myocardial perfusion when using MDCT. The purpose of this work is to present and evaluate a technique termed targeted spatial frequency filtration (TSFF) to reduce CT number variations due to PSR when applied to myocardial perfusion imaging using MDCT. METHODS: The TSFF algorithm requires acquiring enough X-ray projections to reconstruct both partial (π + fan angle α) and full (2π) scans. Then, using spatial linear filters, the TSFF-corrected image data are created by superimposing the low spatial frequency content of the full scan reconstruction (containing no PSR artifacts, but having low spatial resolution and worse temporal resolution) with the high spatial frequency content of the partial scan reconstruction (containing high spatial frequencies and better temporal resolution). The TSFF method was evaluated both in a static anthropomorphic thoracic phantom and using an in vivo porcine model and compared with a previously validated reference standard technique that avoids PSR artifacts by pacing the animal heart in synchrony with the gantry rotation. CT number variations were quantified by measuring the range and standard deviation of CT numbers in selected regions of interest (ROIs) over time. Myocardial perfusion parameters such as blood volume (BV), mean transit time (MTT), and blood flow (BF) were quantified and compared in the in vivo study. RESULTS: Phantom experiments demonstrated that TSFF reduced PSR artifacts by as much as tenfold, depending on the location of the ROI. For the in vivo experiments, the TSFF-corrected data showed two- to threefold decrease in CT number variations. Also, after TSFF, the perfusion parameters had an average difference of 13.1% (range 4.5%-25.6%) relative to the reference method, in contrast to an average difference of 31.8% (range 0.3%-54.0%) between the non-TSFF processed data with the reference method. CONCLUSIONS: TSFF demonstrated consistent reduction in CT number variations due to PSR using controlled phantom and in vivo experiments. TSFF-corrected data provided quantitative measures of perfusion (BV, MTT, and BF) with better agreement to a reference method compared to noncorrected data. Practical implementation of TSFF is expected to incur in an additional radiation exposure of 14%, when tube current is modulated to 20% of its maximum, to complete the needed full scan reconstruction.

Characteristics of Transgender Women Referred to Women's Heart Clinic.

INTRODUCTION: Transgender women have been reported to have a high burden of cardiovascular disease (CVD) and risk factors based largely on surveys. Our aim was to describe the prevalence of CVD and associated comorbidities among a cohort of older transgender women referred to cardiology as part of their gender-affirming care. METHODS: This was a retrospective, cross-sectional study of transgender women at a single institution from 2017 to 2019. RESULTS: Fifty-two consecutive patients were included. The most common reasons for referral were cardiac risk factor management (45%) and pre-operative cardiac risk stratification prior to gender-affirming surgery (35%). The mean age was 57 ± 10 years, 87% were white, and 92% had insurance coverage. Forty-eight patients (92%) were taking gender-affirming hormone therapy; 5 had undergone breast augmentation, 4 had undergone orchiectomy, and 2 had undergone vaginoplasty. The most common comorbidities were depression and/or anxiety (63%), obesity (58%), and hyperlipidemia (54%). Excluding aldosterone antagonists, 46% were on cardiac medications; changes were recommended for 25% of patients: new prescriptions in 9, dose adjustments in 5, and discontinuations in 4. According to the pooled cohort equation, the 10-year risk of atherosclerotic CVD was 9.4 ± 7.7% when the study population was calculated as male and 5.2 ± 5.1% when calculated as female (p <0.001). For patients who completed exercise testing, the functional aerobic capacity was fair (77.6 ± 21.4%) when calculated as male and average (99.5 ± 27.5%) as female (p < .0001); there was inconsistency in sex used for calculating the result on the formal report. CONCLUSIONS: Older transgender women may have an underestimated prevalence of CVD and its risk factors. More research is needed to identify cardiovascular health profiles, improve practice consistency, and establish normative values for transgender patients.

Dual-source dual-energy CT with additional tin filtration: Dose and image quality evaluation in phantoms and in vivo.

OBJECTIVE: The objective of this study was to investigate the effect on radiation dose and image quality of the use of additional spectral filtration for dual-energy CT using dual-source CT (DSCT). MATERIALS AND METHODS: A commercial DSCT scanner was modified by adding tin filtration to the high-kV tube, and radiation output and noise were measured in water phantoms. Dose values for equivalent image noise were compared between the dual-energy mode with and without tin filtration and the single-energy mode. To evaluate dual-energy CT material discrimination, the material-specific dual-energy ratio for calcium and that for iodine were determined using images of anthropomorphic phantoms. Data were additionally acquired from imaging a 38-kg pig and an 87-kg pig, and the noise of the linearly mixed images and virtual noncontrast images was compared between dual-energy modes. Finally, abdominal dual-energy CT images of two patients of similar sizes undergoing clinically indicated CT were compared. RESULTS: Adding tin filtration to the high-kV tube improved the dual-energy contrast between iodine and calcium as much as 290%. Data from our animal study showed that tin filtration had no effect on noise in the dual-energy CT mixed images but decreased noise by as much as 30% in the virtual noncontrast images. Virtual noncontrast images of patients acquired using 100 and 140 kV with added tin filtration had improved image quality relative to those generated using 80 and 140 kV without tin filtration. CONCLUSION: Tin filtration of the high-kV tube of a DSCT scanner increases the ability of dual-energy CT to discriminate between calcium and iodine without increasing dose relative to single-energy CT. Furthermore, the use of 100- and 140-kV tube potentials allows improved dual-energy CT imaging of large patients.

Radiation dose reduction in CT coronary angiography.

During recent years, technologic advancements in computed tomography (CT) have allowed robust cardiac and coronary imaging. Small, mobile cardiac structures such as the coronary arteries can now be imaged directly and noninvasively with high precision. Given the fact that coronary CT angiography (CCTA) can detect preclinical calcified and noncalcified atherosclerosis, there is potential to revolutionize the management of ischemic heart disease by refining risk stratification and improving outcomes in various clinical settings. However, despite this progress, CT has come under scrutiny as concerns about the level and risk of the radiation exposure of the population grow. Although there are no data to support a direct association between CT imaging and risk of future cancer, health care practitioners should make every effort to minimize radiation exposure to their patients. The purpose of this article is to describe techniques that can reduce radiation dose to patients during CCTA but maintain diagnostic image quality.

In vivo vibroacoustography of large peripheral arteries.

OBJECTIVE: Vibroacoustography allows imaging of objects on the basis of their acoustic signal emitted during low-frequency (kHz) vibrations produced by 2 intersecting ultrasound beams at slightly different frequencies. This study tested the feasibility of using vibroacoustography to distinguish between normal and calcified femoral arteries in a pig model. MATERIALS AND METHODS: Thirteen normal porcine femoral arteries, 7 with experimentally induced arterial calcifications, and 1 control artery injected with saline only were scanned in vivo. Images were obtained at 45 kHz using a 3 MHz confocal transducer. The acoustic emission signal was detected with a hydrophone placed on the animal's limb. Images were reconstructed on the basis of the amplitude of the acoustic emission signal. Vessel patency, vessel dimensions, and the extent of calcified plaques were confirmed in vivo by angiography and conventional ultrasound. Excised arteries were reexamined with vibroacoustography, X-ray radiography, and histology. RESULTS: In vivo, vibroacoustography produced high-resolution, speckle-free images with a high level of anatomic detail. Measurements of femoral artery diameter were similar by vibroacoustography and conventional ultrasound (mean difference +/- SD, 0.1 +/- 0.4 mm). Calcified plaque area measured by different methods was comparable (vibroacoustography, in vivo: 1.0 +/- 0.9 cm; vibroacoustography in vitro: 1.1 +/- 0.6 cm2; X-ray radiography: 0.9 +/- 0.6 cm2). The reproducibility of measurements was high. Sensitivity and specificity for detecting calcifications were 100% and 86%, respectively, and positive and negative predictive values were 77% and 100%, respectively. CONCLUSIONS: Vibroacoustography provides accurate and reproducible measurements of femoral arteries and vascular calcifications in living animals.

Computed tomographic angiography of the coronary arteries: techniques and applications.

Computed tomographic coronary angiography (CT-CA) is a direct but minimally invasive method of visualizing coronary arteries. Multidetector-row computed tomography (MDCT) is currently the CT modality most commonly used for coronary artery imaging. MDCT has been successfully used to detect stenoses in coronary arteries and coronary artery bypass grafts and to assess congenital coronary anomalies. Patients should not undergo CT-CA with MDCT if they have an irregular heart rhythm, a heart rate greater than 70 beats/min, and contraindications to pharmacologic agents for heart rate control, or if they have severe coronary artery disease or are likely to require revascularization.

Effect of acquisition technique on radiation dose and image quality in multidetector row computed tomography coronary angiography with submillimeter collimation.

RATIONALE AND OBJECTIVES: We sought to examine effects of tube voltage and current on radiation dose and image quality for minimally invasive coronary angiography with a 16-slice multidetector row computed tomography (MDCT) scanner. MATERIALS AND METHODS: We scanned the phantom used in the American College of Radiology Computed Tomography Accreditation Program at tube voltages of 80 and 120 kVp at 550, 650, and 750 mAseff, with and without a reduction in radiation dose by electrocardiographically (ECG) controlled tube current modulation (ECG pulsing). RESULTS: Without ECG pulsing, the effective dose was 3 to 13 mSv. On average, a 50% increase in tube voltage led to increased radiation dose (215%), contrast-to-noise ratio (150%), and decreased image noise (-48%). On average, a 17% increase in mAseff led to increased radiation dose (17%) and contrast-to-noise ratio (4%) and decreased image noise (-9%). Dose reduction by ECG pulsing (simulated heart rate, 70 beats per minute) was 28%. With ECG pulsing, noise in images reconstructed during ventricular systole was double that in images reconstructed during ventricular diastole. CONCLUSIONS: These quantitative findings about the relationships among scan acquisition parameters, radiation dose, and image quality have practical implications for using ECG pulsing to reduce radiation doses in MDCT coronary angiography.

Imaging of myocardial microvasculature using fast computed tomography and three-dimensional microscopic computed tomography.

In the past, much attention in imaging research was focused on the macroscopic morphology and patency of arteries. Only recently, research and clinical interest have shifted to the microcirculation and its impact on the long-term prognosis in patients with vascular diseases. This focus and newly developed therapeutic strategies require high-resolution imaging modalities, which do not focus exclusively on the macroscopic aspects of the arterial tree. Provided here is a comprehensive perspective of using computed tomography technology to image and quantify the function and morphology of myocardial and vascular adventitial microvessels in normal and disease states.

Cryostatic micro-computed tomography imaging of arterial wall perfusion.

A double-walled copper vessel, 32 cc in volume, was fabricated for scanning tissue specimens while maintained below freezing point. To keep specimen temperature within +/- 1 degrees C, temperature sensors within the chamber control, the rate of inflow of the cold nitrogen gas vented through the chamber. The specimen is attached to a small platform on top of a vertical pin which is attached to the computer-controlled rotating stage under the vessel. The purpose of this arrangement is to permit scanning of specimens up to 2 cm3 that (1) cannot be "fixed" (e.g., with formalin) because of analyses which are incompatible with prior fixation (certain immunohistochemistry and biomolecular methods), or (2) are "snap"-frozen during a transient process, such as the accumulation and/or washout of radiopaque indicators. Examples of "cryoscans" of porcine carotid and coronary artery wall opacification in either untouched or acutely stented arteries, snap-frozen immediately after selective intra-arterial injection of a contrast agent, show accumulation of contrast in the extravascular space indicating increased endothelial permeability or endothelial and medial disruption following stent placement. The detection of contrast in the adventitia suggest that vasa vasorum deliver the contrast agent from the main lumen to the adventitial extravascular space but not to the media.

Assessing the available techniques for testing myocardial viability: what does the future hold?

Left ventricular dysfunction in the setting of severe coronary artery disease poses a major diagnostic and therapeutic dilemma. While this clinical scenario is generally associated with poor outcomes, some but not all patients benefit from coronary revascularization. For example, patients with severe, transmural myocardial infarctions may derive little or no functional benefit from revascularization, as the underlying myocardium is irreversibly scarred. Furthermore, these patients may be exposed to high procedural risks with a low likelihood of deriving any perceivable benefit. Conversely, hibernating myocardium reflects a substrate whereby the nonfunctioning myocytes are chronically ischemic but may be viable. Existing data are somewhat inconclusive with regard to the benefits of performing viability testing in patients with ischemic cardiomyopathy. While this testing may predict regional and global functional myocardial recovery, the ability of viability studies to predict survival and prognosis remains unproven in prospective studies to date. Yet, viability testing may still be a valuable tool to guide therapeutic options in selected patients. A variety of noninvasive viability tests are available and newer technologies, such as PET and cardiac MRI, are likely to advance the scientific field in years to come.

Quantification of iron in the presence of calcium with dual-energy computed tomography (DECT) in an ex vivo porcine plaque model.

Iron deposits secondary to microbleeds often co-exist with calcium in coronary plaques. The purpose of this study was to quantify iron in the presence of calcium in an ex vivo porcine arterial plaque model using a clinical dual-energy CT (DECT) scanner. A material decomposition method to quantify the mass fractions of iron and calcium within a mixture using DECT was developed. Mixture solutions of known iron and calcium concentrations were prepared to calibrate and validate the DECT-based algorithm. Simulated plaques with co-existing iron and calcium were created by injecting the mixture solutions into the vessel wall of porcine carotid arteries and aortas. These vessel regions were harvested and scanned using a clinical DECT system and iron mass fraction was calculated for each sample. Iron- and calcium-specific staining was conducted on 5 µm thick histological sections of vessel samples to confirm the co-existence of iron and calcium in the simulated plaques. The proposed algorithm accurately quantified iron and calcium amounts in mixture solutions. Maps of iron mass fraction of 60 artery segments were obtained from CT images at two energies. The sensitivity for detecting the presence of iron was 83% and the specificity was 92% using a threshold at an iron mass fraction of 0.25%. Histological analysis confirmed the co-localization of iron and calcium within the simulated plaques. Iron quantification in the presence of calcium was feasible in excised arteries at an iron mass fraction of around 1.5% or higher using current clinical DECT scanners.

Thrombus of the internal carotid artery: the contribution of computed tomographic angiography to clinical management.

Intraluminal thrombus adjunct to internal carotid artery plaque is a rare finding on traditional diagnostic imaging. Prompt diagnosis is important as it carries a high risk of recurrent stroke. We describe 2 symptomatic patients with severe stenosis on duplex scanning and internal carotid artery thrombus (ICAT) identified on subsequent computed tomographic angiography. Histology of the surgical specimen confirmed the composition predicted by computed tomography. Computed tomographic angiography can provide accurate diagnosis and characterization of internal carotid thrombus and lead to prompt therapeutic intervention.

Radiation dose and safety in cardiac computed tomography.

As a result of the changes in use of imaging procedures that rely on ionizing radiation, the collective dose has increased by over 700%, and the annual per-capita dose by almost 600% in recent years. It is possible that this growing use may have significant effects on public health. Although uncertainties exist related to the accuracy of estimated radiation exposure and biologic risk, there are measures that can be taken by the referring and the performing health care provider to reduce the potential risks while maintaining diagnostic accuracy. This article reviews the existing data regarding biologic hazards of radiation exposure associated with medical diagnostic testing, the methodologies used to estimate radiation exposure and dose, and the measures that can be taken to effectively reduce that exposure.

Coronary computed tomographic angiography: current role in the diagnosis and management of coronary artery disease.

Advances in computed tomography (CT) technology allow images to be obtained with high spatial and temporal resolution. These features now permit noninvasive coronary CT angiography (CCTA). Many studies addressing proof of concept, feasibility, and clinical robustness have been published since CCTA was first described. More recently, the scientific evaluation of CCTA has rightly focused less on technical aspects and more on multicenter trials of the diagnostic value of CCTA and on head-to-head comparisons with other noninvasive modalities for the detection of coronary artery disease (CAD), such as stress myocardial perfusion imaging (MPI) with radionuclides. Recent peer-reviewed publications that compare CCTA to invasive, selective coronary angiography (SCA) or MPI, or that address radiation protection issues related to CCTA, were reviewed and summarized. Overall, there is high agreement between CCTA and both SCA and MPI for the presence of CAD. However, CCTA can over- or underestimate the severity of CAD compared to SCA as a reference standard. Initial studies that compared CCTA to MPI found their accuracies for determining the presence of high-grade luminal obstructions comparable. Limitations of CCTA include inability to reliably assess the coronary artery lumen dimensions in patients with large amounts of coronary artery calcium, artifacts caused by coronary and respiratory motion, and the need for ionizing radiation and intravenous administration of iodinated contrast material. Various dose reduction methods for CCTA now exist that may substantially lower patient dose to levels less than those of SCA or MPI. Although current expert consensus does not call for CCTA to be a first-line test for CAD, particularly for screening in asymptomatic individuals, current data suggest a promising role in the evaluation of symptomatic patients for possible CAD.

Coronary computed tomography and magnetic resonance imaging.

Cardiac computed tomography and magnetic resonance are relatively new imaging modalities that can exceed the ability of established imaging modalities to detect present pathology or predict patient outcomes. Coronary calcium scoring may be useful in asymptomatic patients at intermediate risk. Computed tomographic coronary angiography is a first-line indication to evaluate congenitally abnormal coronary arteries and, along with stress magnetic resonance myocardial perfusion imaging, is useful in symptomatic patients with nondiagnostic conventional stress tests. Cardiac magnetic resonance is indicated for visualizing cardiac structure and function, and delayed enhancement magnetic resonance is a first-line indication for assessing myocardial viability. Imaging plaque and molecular mechanisms related to plaque rupture holds great promise for the presymptomatic detection of patients at risk for coronary events but is not yet suitable for routine clinical use.

Coronary computed tomographic angiography: current and future uses.

Coronary computed tomographic angiography (CCTA) is a direct but minimally invasive method of visualizing coronary arteries. Acceptable indications for this technique include the assessment of suspected or known coronary artery anomalies, the evaluation of chest pain syndromes in patients with non diagnostic stress tests or who are unable to exercise, and exclusion of an ischemic etiology in patients with unexplained left ventricular dysfunction. Assessment of coronary stents with a diameter of <3.0 mm and imaging of asymptomatic patients with a goal of establishing prognosis are currently not accepted indications for CCTA.