Yogesh Thakur

Coronary CT Angiography of Patients With a Normal Body Mass Index Using 80 kVp Versus 100 kVp: A Prospective, Multicenter, Multivendor Randomized Trial

OBJECTIVE We determined the effect of reduced 80-kVp tube voltage on the radiation dose and image quality of coronary CT angiography (CTA) in patients with a normal body mass index (BMI). SUBJECTS AND METHODS A prospective, multicenter, multivendor trial was performed of 208 consecutive patients with a normal BMI (< 25 kg/m(2)) who had been referred for coronary CTA and did not have a history of coronary revascularization. Patients were randomized to 80-kVp imaging (n = 103) or 100-kVp imaging (n = 105). Three blinded readers graded interpretability and image quality. Study signal, noise, and contrast were also compared. RESULTS Imaging with 80 kVp instead of 100 kVp was associated with 47% lower median radiation dose (median dose-length product, 62.0 mGy · cm [interquartile range, 54.0-123.3 mGy · cm] vs 117.0 mGy · cm [110.0-225.9 mGy · cm], respectively; 0.9 mSv [0.8-1.7 mSv] vs 1.6 mSv [1.4-3.2 mSv]; p < 0.001 for each) with no significant difference in interpretability (99% vs 99%; p = 0.99) or image quality (median score, 4.0 [interquartile range, 3.6-4.0] vs 4.0 [interquartile range, 3.8-4.0]; p = 0.20). Studies obtained using 80 kVp were associated with 27% increased signal (mean ± SD, 756 ± 157 vs 594 ± 105 HU; p < 0.001), 25% higher contrast (890 ± 156 vs 709 ± 108 HU; p < 0.001), and 50% greater noise (55 ± 15 vs 37 ± 12 HU; p < 0.001) with resultant 15% and 16% decreases in signal-to-noise (mean ± SD, 15 ± 5 vs 17 ± 5; p < 0.001) and contrast-to-noise (mean ± SD, 17 ± 6 vs 21 ± 5; p < 0.001) ratios, respectively. CONCLUSION Coronary CTA using 80 kVp instead of 100 kVp was associated with a nearly 50% reduction in radiation dose with no significant difference in interpretability and noninferior image quality despite lower signal-to-noise and contrast-to-noise ratios. The use of 80-kVp tube voltage should be considered in dose-reduction strategies for coronary CTA of individuals with a normal BMI.

Pulmonary CT Angiography as First-Line Imaging for PE: Image Quality and Radiation Dose Considerations

OBJECTIVE This article reviews dose reduction techniques in pulmonary CT angiography (CTA) for imaging pulmonary embolism (PE). Dose reduction technologies covered include tube current modulation, kilovoltage modulation, scanning length modification, dynamic z-axis collimation, iterative reconstruction, and dual-energy CT. Age- and weight-specific imaging techniques are suggested. CONCLUSION Pulmonary CTA plays a vital role in imaging PE. Using dose reduction technologies can provide high-quality diagnostic imaging with a significant reduction in patient dose.

Risk-Benefit Analysis of Pulmonary CT Angiography in Patients With Suspected Pulmonary Embolus

OBJECTIVE The objective of our study was to estimate the mortality benefit-to-risk ratio of pulmonary CT angiography (CTA) by setting (ambulatory [emergency department or outpatient] or inpatient), age, and sex. MATERIALS AND METHODS A retrospective evaluation of 1424 consecutive pulmonary CTA examinations was performed and the following information was recorded: examination setting, patient age, patient sex, pulmonary CTA interpretation for pulmonary embolus (PE), and CT radiation exposure (dose-length product). We estimated mortality benefit of pulmonary CTA by multiplying the rate of positive pulmonary CTA examinations by published estimates of mortality of untreated PE in ambulatory and inpatient settings. We estimated the lifetime attributable risk of cancer mortality due to radiation from pulmonary CTA by calculating the estimated effective dose and using sex-specific polynomial equations derived from the Biological Effects of Ionizing Radiation VII report. We calculated benefit-to-risk ratios by dividing the mortality benefit of preventing a fatal PE by the mortality risk of a radiation-induced cancer. RESULTS Pulmonary CTA diagnosed PE in 188 of 1424 patients (13.2%). Both inpatients (101/723, 14.0%) and emergency department patients (74/509, 14.5%) had significantly higher rates of PE than outpatients (13/192 [6.8%]). Males received significantly (p = 0.02451) higher radiation dose (9.7 mSv) than females (8.4 mSv), but males had a significantly (p < 0.0001) lower lifetime attributable risk of cancer mortality than females. Assuming an untreated PE mortality rate of 5% for ambulatory patients and 30% for inpatients, the benefit-to-risk ratio ranged from 25 for ambulatory patients to 187 for inpatients. Ambulatory women had the lowest benefit-to-risk ratio. CONCLUSION The benefit-to-risk ratio of pulmonary CTA in patients with suspected PE ranges from 25 to 187 and can be increased by optimizing the radiation dose.

Scanner and kVp dependence of measured CT numbers in the ACR CT phantom

Quality control testing of CT scanners in our region includes a measurement of CT numbers in the American College of Radiology (ACR) CT phantom using a standardized protocol. CT number values are clinically relevant in determining the composition of various tissues in the body. Accuracy is important in the characterization of tumors, assessment of coronary calcium, and identification of urinary stone composition. Effective quality control requires that tolerance ranges of CT number values be defined: a measured value outside the range indicates the need for further investigation and possible recalibration of the scanner. This paper presents the results of CT number measurements on 36 scanners (25 GE, 10 Siemens and 1 Toshiba) at each available kVp. Among the five materials (solid water, air, polyethylene, acrylic, bone‐equivalent) the measured CT numbers exhibit manufacturer and kVp dependence, which should be taken into account when defining tolerances. With this scan protocol, air and solid water values are significantly higher on GE scanners than on Siemens scanners (p‐value<0.01 at each kVp). The CT numbers of polyethylene and acrylic increase with kVp, while the bone‐equivalent CT number decreases. These results are used to define manufacturer‐ and kVp‐specific tolerance ranges for the CT numbers of each material in this phantom, which will be used in our quality control program. PACS numbers: 87.57.qp, 87.57.C‐

Organ-based computed tomographic (CT) radiation dose reduction to the lenses: impact on image quality for CT of the head.

Purpose Recently, a new specific organ dose adaption and reduction protocol, or SODAR tool (X-CARE, Siemens Healthcare), which reduces dose to the anterior aspect of the body of patients, was installed on our computed tomographic scanner. The purpose of this pilot project was to evaluate image quality and dose distribution in the acquired data with the new protocol. Materials and Methods Sixteen consecutive patients were scanned with the new SODAR head protocol. The findings were compared with 16 matched patients who were imaged with the standard computed tomographic head trauma protocol. Image quality was assessed qualitatively using a scale of 1 to 4 (1, excellent; 2, good; 3, fair; 4, nondiagnostic). Additionally, 1-cm2 regions of interest were placed in the white matter of the cerebral hemispheres, the cerebellar hemispheres, and the brain stem at the level of the pons for a quantitative analysis. The standard deviation of each measurement was recorded as an indicator for image noise. Dose measurement trials were performed using optically stimulated luminescence dosimeters on head phantoms and then on patients. Results Subjective image quality ranged between 1 and 3; no scan areas were considered nondiagnostic. Overall image quality of the posterior fossa averaged at 1.656 was slightly reduced compared to the cerebral hemispheres (mean, 1.141). The mean standard protocol brain stem image quality was 1.604, with only minimal deterioration to 1.708 in the SODAR group. No significant difference in image noise could be found between the SODAR group with a mean noise of 4.515 and standard images with a mean of 4.721 (P > 0.05). The dose to the anterior aspect of the patient was lowered to 3.2 mGy compared to 4.5 mGy on the lateral aspect of the scan (P > 0.05). To compensate for the photon loss in the posterior aspect, the dose has to be slightly increased to a mean of 6 mGy, but overall, a significant dose reduction with stable image quality could be achieved by reducing the dose length product from 1489 to 1347 mGy·cm using SODAR (P < 0.0001). Conclusion Using the SODAR protocol resulted not only in an impressive 46% to 59% frontal dose reduction but also in the overall dose reduction. This dose reduction was obtained without sacrificing image quality, providing diagnostic images of the brain while protecting radiosensitive structures like the eye lenses in trauma brain imaging. Future applications will be reducing dose to other radiosensitive structures such as the thyroid gland and breast tissue from potentially harmful low-energy radiation without compromising image quality.

A Magnetic-Resonance-Imaging-Compatible Remote Catheter Navigation System

A remote catheter navigation system compatible with magnetic resonance imaging (MRI) has been developed to facilitate MRI-guided catheterization procedures. The interventionalists conventional motions (axial motion and rotation) on an input catheter - acting as the master - are measured by a pair of optical encoders, and a custom embedded system relays the motions to a pair of ultrasonic motors. The ultrasonic motors drive the patient catheter (slave) within the MRI scanner, replicating the motion of the input catheter. The performance of the remote catheter navigation system was evaluated in terms of accuracy and delay of motion replication outside and within the bore of the magnet. While inside the scanner bore, motion accuracy was characterized during the acquisition of frequently used imaging sequences, including real-time gradient echo. The effect of the catheter navigation system on image signal-to-noise ratio (SNR) was also evaluated. The results show that the master-slave system has a maximum time delay of 41 ± 21 ms in replicating motion; an absolute value error of 2 ± 2° was measured for radial catheter motion replication over 360° and 1.0 ± 0.8 mm in axial catheter motion replication over 100 mm of travel. The worst-case SNR drop was observed to be 2.5%.

Strategies for Radiation Dose Optimization

This article reviews strategies for radiation dose optimization for computed tomography (CT). A brief overview of dose metrics including computed tomographic dose index, dose length product and effective dose is provided. The impact of age and gender on the sensitivity to radiation is discussed with the aim of tailoring CT acquisition parameters to patient demographics. Dose reduction technologies are reviewed including: tube current modulation, kVp modulation, scan length modification, dynamic z-axis collimation, iterative reconstruction and dual energy. Optimal selection of CT acquisition parameters requires review of clinical information and patient demographics prior to imaging. The authors conclude that with the appropriate application of dose reduction technologies there can be substantial reduction in patient radiation dose while maintaining high diagnostic quality images.

Acute Pulmonary Embolism: From Morphology to Function

This article reviews the current diagnostic strategies for patients with suspected pulmonary embolism (PE) focusing on the current first choice imaging modality, computed tomographic pulmonary angiography (CTPA). Diagnostic strengths and weaknesses and associated cost-effectiveness of the diagnostic pathways will be discussed. The radiation dose risk of these pathways will be described and techniques to minimize dose will be reviewed. Finally the impact of new dual energy applications which have the potential to provide additional functional information will be briefly reviewed. Imaging plays a vital role in the diagnostic pathway for clinically suspected PE. CT has been established as the most robust morphologic imaging tool for the evaluation of patients with suspected PE. This conclusion is based on the high diagnostic utility of CT for the detection of PE and its unique capacity for accurate diagnosis of conditions that can mimic the clinical presentation of PE. Although current cost-effectiveness evaluations have established CT as integral in the PE diagnostic pathway, failure to acknowledge the impact of alternate diagnosis represents a current knowledge gap. The emerging dual energy capacity of current CT scanners offers the potential to evaluate both pulmonary vascular morphology and ventilation perfusion relationships within the lung parenchyma at high spatial resolution. This dual assessment of lung morphology and lung function at low (< 5 millisievert) radiation dose represents a substantial advance in PE imaging.

Canadian Association of Radiologists Radiation Protection Working Group: Review of Radiation Units and the Use of Computed Tomography Dose Indicators in Canada

Radiation has played a vital role in health care for overa century now. Since Roentgen’s first radiograph in 1895, themedical imaging community has made tremendous advanceswith imaging technology, leading to earlier detectionof disease, minimally invasive approaches to diagnosisand therapy, and, most importantly, improved patientoutcome.Ionizing radiation can directly damage tissue and isrecognized by multiple national and international bodies asa weak carcinogen [1e3]. Direct tissue damage is referred toas the deterministic effect of radiation and will occur afterthe patient receives a radiation dose that exceeds a threshold,whereas the risk of cancer is referred to as a random orstochastic effect, with the probability of developing cancerincreasing with increasing radiation dose to the patient. Bothdeterministic and stochastic effects are a function ofradiation dose, a concept with multiple terminologies thathas led to significant confusion in practice. With an increasedreliance on medical imaging for patient care, both the short-and long-term risks associated with each imaging proceduremust be understood by all practitioners. The CanadianAssociation of Radiologists (CAR) has formed the RadiationProtection Working Group (RPWG) to provide leadership ondose education in Canada. This group aims to developstandards on diagnostic medical radiation protection todecrease patient risk and provide the CAR membership withinformation, online dose-calculating tools, and a forum todiscuss medical radiation dose in Canada.In this first essay, 3 important concepts will be discussed:radiation risk models, radiation units and the dose deliveredby medical imaging systems, and the estimated radiationdose received by the patient. Because computed tomographic(CT) examinations account for the majority of total radiationreceived by patients, especially when considering thedisproportionately lower examination frequency comparedwith other medical imaging examinations [4,5], theseconcepts will be discussed with a specific emphasize on dosefrom common CT examinations.

Radiation Dose Survey for Common Computed Tomography Exams: 2013 British Columbia Results

In 2013 Health Canada conducted a national survey of computed tomography (CT) radiation usage. We analysed contributions from all 7 public health authorities in the province of British Columbia, which covered scanner age, number of slices, and common adult protocols (≥19 years: 70 ± 20 kg, head, chest, abdomen/pelvis, and trunk). Patient doses were recorded for common protocols. Diagnostic reference levels (DRLs) was calculated using scanner data with >10 patient doses recorded for each protocol. Data was analysed based on image reconstruction (filtered backprojection vs iterative reconstruction [IR] vs IR available but not in use). Provincial response was 92%, with 59 of 64 CT data used for analysis. The average scanner age was 5.5 years old, with 39% of scanners installed between 2008-2013; 78.5% of scanners were multislice (>64 slices), and 44% of scanners had IR available. Overall British Columbia DRLs were: head = 1305, chest = 529, abdomen/pelvis = 819, and trunk = 1225. DRLs were consistent with Health Canada recommendations and other Canadian published values, but above international standards. For sites with IR available, less than 50% used this technology routinely for head, chest and trunk exams. Overall, use of IR reduced radiation usage between 11%-32% compared to filtered backprojection, while sites using IR vs IR available used 30%/43% less radiation for head/chest exams (P < .05). No significant difference was observed for abdomen/pelvis exams (P = .385). With the fast pace of CT technical advancement, DRLs should reflect the technology used, instead of just globally applied to anatomical regions. Federal guidelines should be updated at a higher frequency to reflect new technology. In addition, new technologies must be utilised to optimize image quality vs radiation usage.