Overview
In the past decade, the tremendous advances in computed tomography (CT) technology and applications have increased the clinical utilization of CT, creating concerns about individual and population doses of ionizing radiation.
Scanner manufacturers have subsequently implemented several options to appropriately manage or reduce the radiation dose from CT.
Modulation of the x-ray tube current during scanning is one effective method of managing the dose. However, the distinctions between the various tube current modulation products are not clear from the product names or descriptions.
Depending on the scanner model, the tube current may be modulated according to patient attenuation or a sinusoidal-type function. The modulation may be fully preprogrammed, implemented in near-real time by using a feedback mechanism, or achieved with both preprogramming and a feedback loop.
The dose modulation may occur angularly around the patient, along the long axis of the patient, or both.
Finally, the system may allow the use of one of several algorithms to automatically adjust the current to achieve the desired image quality. Modulation both angularly around the patient and along the z-axis is optimal, but the tube current must be appropriately adapted to patient size for diagnostic image quality to be achieved.
Answering a growing demand for radiation dose reduction in cardiac CT scanning, GE Healthcare announced the release of “SnapShot Pulse” at a national meeting earlier this month.
This advancement in technology will achieve up to an 83% reduction in the patient’s radiation exposure as well as improve image quality.
Los Angeles CT Scan expert explains.
The average American’s total radiation exposure has nearly doubled since 1980, largely because of CT scans. Medical radiation now accounts for more than half of the population’s total exposure; it used to be just one-sixth, and the top source was the normal background rate in the environment, from things like radon in soil and cosmic energy from the sun.
But CT use continues to soar.
About 62 million scans were done in the U.S. last year, up from 3 million in 1980.
Los Angeles CT scans became popular because they offer a quick, relatively cheap, and painless way to get 3D pictures so detailed they give an almost surgical view into the body. But they put out a lot of radiation.
In a few decades, as many as 2 percent of all cancers in the United States might be due to radiation from CT scans given now, according to the authors of a recent report in the New England Journal of Medicine.
A CT scan of the chest involves 10 to 15 millisieverts (a measure of dose) versus 0.01 to 0.15 for a regular chest X-ray, 3 for a mammogram, and a mere 0.005 for a dental X-ray.
The dose depends on the type of machine and the person — obese people require more radiation than slim ones — and the risk accumulates over a lifetime.
Cardiac CT scanning in Los Angeles has, in the last few years, has been increasingly become part of the diagnostic armamentarium available to cardiologists in their quest for an early and accurate diagnosis of heart disease in selected patient populations.
Radiation exposure from these studies is nonetheless significant, and should always be discussed with the patient in the context of risk versus benefit.
Radiation Dose Reduction by Using CT with Iterative Model Reconstruction in Patients
Purpose
To compare the diagnostic quality of reduced radiation dose computed tomography (CT) with iterative model reconstruction (IMR) versus that of conventional low-dose CT in patients with pulmonary invasive fungal infection.
Materials and Methods
This prospective observational study included 48 patients (mean age ± standard deviation, 39.9 years ± 11.3) known to have or suspected of having pulmonary invasive fungal infection between October 2016 and July 2017.
Patients underwent CT with IMR (at 80 kV with 20 mA) immediately after low-dose CT (at 80 kV with automatic exposure control). Images were reconstructed by using a hybrid iterative reconstruction (HIR) algorithm and IMR.
Two radiologists independently assessed subjective image quality, noise, and visibility of normal and abnormal findings by using a five-point scale.
Objective measurements, including image noise, contrast-to-noise ratio (CNR), and corresponding figure of merit (FOM), were compared by using repeated-measures analysis of variance with Bonferroni post hoc tests for multiple comparisons.
Results
The mean effective dose was 0.3 mSv ± 0.3 for CT with IMR and 0.7 mSv ± 0.2 for low-dose CT (P < .01). When the image noise and CNR were normalized to the effective dose, CT images obtained with IMR had significantly higher FOM than did other image series (P < .0001).
Subjectively, visibility of CT features of invasive fungal infection on CT scans reconstructed with IMR was rated as noninferior to that on low-dose CT scans reconstructed with HIR, except for the halo sign.
Conclusion
CT with IMR had approximately 60% dose reduction compared with conventional low-dose CT, with reduced noise and improved depiction of abnormal discovery
Introduction
The incidence of invasive fungal infections with particularly high mortality is increasing in severely immunocompromised patients with neutropenia and hematologic malignancies.
Computed tomography (CT) is now regarded as the first-line imaging method to detect pulmonary invasive fungal infection or to evaluate antifungal treatment response.
However, this technique is criticized for high cumulative radiation exposure with potential long-term effects, in particular when used for multiple follow-up CT examinations during the illness.
Several strategies have been developed to reduce the radiation burden related to CT One promising approach involves iterative reconstruction techniques, which can substantially reduce image noise when compared with reconstruction that involves conventional filtered back-projection with scanning at lower radiation doses (7).
Recent use of hybrid-type iterative reconstruction has shown much promise in improving image quality by iteratively repeating back-projection multiple times (8–11).
The next evolution of this knowledge-based iterative reconstruction technique has recently been developed and offers the possibility of a further reduction in image noise while improving spatial resolution through iterative use of both back and forward projections (12–19).
Recent clinical studies have shown knowledge-based iterative reconstruction to be useful in the chest, coronary (13), heart disease, lumbar (16), brain (17), and abdominal (18) CT to reduce noise at low-dose scanning.
However, to our knowledge, there have been no published data on their application for the specific depiction of pulmonary invasive fungal infection.
We hypothesized that combining low-tube-voltage (80 kVp) CT with this clinically feasible iterative model reconstruction (IMR) technique could provide diagnostically acceptable image quality with substantial radiation dose reduction.
Therefore, this study aimed to compare the image quality and visibility of abnormal findings on CT images reconstructed with IMR and low-dose CT images reconstructed with a hybrid iterative reconstruction (HIR) algorithm in patients with pulmonary invasive fungal infection.
Materials and Methods
This prospective, single-institution, observational study was approved by our institutional review board. Written informed consent was obtained from all participants. This study was based on a retrospective interpretation of prospectively acquired data.
Patient Population
Between October 2016 and July 2017, 236 consecutive patients identified by the hematology departments for chest CT indicated for invasive fungal infection were enrolled.
The inclusion criteria were the age of at least 18 years; host factors according to the 2008 criteria from the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (); clinical symptoms and signs, including persistent fever refractory to broad-spectrum antibiotics (>48 hours); and other nonspecific manifestations, such as cough, pleural pain, or hemoptysis, in patients scheduled for chest CT.
Patients who were unable to provide written informed consent or to follow verbal commands for breath holding during CT. were excluded.
Patients who showed no typical invasive fungal infection features (eg, nodules or consolidations) on review of the low-dose CT images were also excluded from presenting the flowchart of the study design.
Unnecessary tests should be canceled, breast shields should be made use of, and the latest technology that permits diagnostic quality studies while minimizing radiation exposure necessary to produce them should be utilized.
On this last note, GE’s “SnapShot Pulse” is only the latest in what appears to be a continued effort by the industry to evolve the technology to minimize radiation exposure in the cardiac CT field.
