Atif N. Khan

Interplay of coronary artery calcification and traditional risk factors for the prediction of all-cause mortality in asymptomatic individuals.

Background— Current guidelines recommend the use of coronary artery calcium (CAC) scoring for intermediate-risk patients; however, the potential role of CAC among individuals who have no risk factors (RFs) is less established. We sought to examine the relationship between the presence and burden of traditional RFs and CAC for the prediction of all-cause mortality. Methods and Results— The study cohort consisted of 44 052 consecutive asymptomatic individuals free of known coronary heart disease referred for computed tomography for the assessment of CAC. The following RFs were considered: (1) current cigarette smoking, (2) dyslipidemia, (3) diabetes mellitus, (4) hypertension, and (5) family history of coronary heart disease. Patients were followed for a mean of 5.6±2.6 years for the primary end point of all-cause mortality. Among individuals who had no RF, Cox proportional model adjusted for age and sex identified that increasing CAC scores were associated with 3.00- to 13.38-fold higher mortality risk. The lowest survival rate was observed in those with no CAC and no RF, whereas those with CAC≥400 and ≥3 RFs had the highest all-cause fatality rate. Notably, individuals with no RF and CAC≥400 had a substantially higher mortality rate compared with individuals with ≥3 RFs in the absence of CAC (16.89 versus 2.72 per 1000 person-years). Conclusions— By highlighting that individuals without RFs but elevated CAC have a substantially higher event rates than those who have multiple RFs but no CAC, these findings challenge the exclusive use of traditional risk assessment algorithms for guiding the intensity of primary prevention therapies.

Relation of Aortic Valve Calcium Detected by Cardiac Computed Tomography to All-Cause Mortality

Aortic valve calcium (AVC) can be quantified on the same computed tomographic scan as coronary artery calcium (CAC). Although CAC is an established predictor of cardiovascular events, limited evidence is available for an independent predictive value for AVC. We studied a cohort of 8,401 asymptomatic subjects (mean age 53 ± 10 years, 69% men), who were free of known coronary heart disease and were undergoing electron beam computed tomography for assessment of subclinical atherosclerosis. The patients were followed for a median of 5 years (range 1 to 7) for the occurrence of mortality from any cause. Multivariate Cox regression models were developed to predict all-cause mortality according to the presence of AVC. A total of 517 patients (6%) had AVC on electron beam computed tomography. During follow-up, 124 patients died (1.5%), for an overall survival rate of 96.1% and 98.7% for those with and without AVC, respectively (hazard ratio 3.39, 95% confidence interval 2.09 to 5.49). After adjustment for age, gender, hypertension, dyslipidemia, diabetes mellitus, smoking, and a family history of premature coronary heart disease, AVC remained a significant predictor of mortality (hazard ratio 1.82, 95% confidence interval 1.11 to 2.98). Likelihood ratio chi-square statistics demonstrated that the addition of AVC contributed significantly to the prediction of mortality in a model adjusted for traditional risk factors (chi-square = 5.03, p = 0.03) as well as traditional risk factors plus the presence of CAC (chi-square = 3.58, p = 0.05). In conclusion, AVC was associated with increased all-cause mortality, independent of the traditional risk factors and the presence of CAC.

Anterior Versus Lateral Needle Decompression of Tension Pneumothorax: Comparison by Computed Tomography Chest Wall Measurement

OBJECTIVES Recent research describes failed needle decompression in the anterior position. It has been hypothesized that a lateral approach may be more successful. The aim of this study was to identify the optimal site for needle decompression. METHODS A retrospective study was conducted of emergency department (ED) patients who underwent computed tomography (CT) of the chest as part of their evaluation for blunt trauma. A convenience sample of 159 patients was formed by reviewing consecutive scans of eligible patients. Six measurements from the skin surface to the pleural surface were made for each patient: anterior second intercostal space, lateral fourth intercostal space, and lateral fifth intercostal space on the left and right sides. RESULTS The distance from skin to pleura at the anterior second intercostal space averaged 46.3 mm on the right and 45.2 mm on the left. The distance at the midaxillary line in the fourth intercostal space was 63.7 mm on the right and 62.1 mm on the left. In the fifth intercostal space the distance was 53.8 mm on the right and 52.9 mm on the left. The distance of the anterior approach was statistically less when compared to both intercostal spaces (p < 0.01). CONCLUSIONS With commonly available angiocatheters, the lateral approach is less likely to be successful than the anterior approach. The anterior approach may fail in many patients as well. Longer angiocatheters may increase the chances of decompression, but would also carry a higher risk of damage to surrounding vital structures.

Prevalence of Non-Cardiac Pathology on Clinical Transthoracic Echocardiography

BACKGROUND Non-cardiac findings (NCFs) are seen in more than a third of cardiac computed tomographic and cardiac magnetic resonance imaging studies. The prevalence and importance of NCFs in transthoracic echocardiographic (TTE) imaging is unknown. The aim of this study was to determine the prevalence of NCFs on TTE imaging. METHODS The subcostal images of all comprehensive adult TTE studies performed at one institution in December 2008 were retrospectively reviewed for NCFs by a radiologist with fellowship training in cardiovascular and abdominal radiology and blinded to the TTE report findings and clinical histories. Additional TTE image orientations were assessed in a subset of 300 studies. NCFs were categorized as benign (e.g., simple hepatic cyst), indeterminate (e.g., ascites), or worrisome (e.g., liver metastases). If an indeterminate or worrisome NCF was identified, the patients electronic medical record was reviewed to determine if the NCF was previously known. RESULTS Of 1,008 TTE studies (443 inpatient, 565 outpatient) in 922 patients, 77 NCFs were identified in 69 patients (7.5%). These included 20 benign (26%), 52 indeterminate (67%), and five worrisome (7%) NCFs. Intermediate and worrisome NCFs were more common in inpatient TTE studies (9% vs 3% outpatient, P = .002). The additional views demonstrated 2% more NCFs. Record review demonstrated that 60% of worrisome and 67% of indeterminate NCFs were previously known. No unknown NCF ultimately led to a change in patient management. CONCLUSIONS Clinical TTE studies demonstrate NCFs in 7.5% of all patients, with an increased prevalence on inpatient studies. Although 75% of NCFs were potentially management changing, the majority of these were previously known and very unlikely to lead to management changes. Further study is needed to validate these findings in other populations and to assess their clinical impact.

Absorbed Radiation Dose in Radiosensitive Organs During Coronary CT Angiography Using 320-MDCT: Effect of Maximum Tube Voltage and Heart Rate Variations

OBJECTIVE The purpose of this article is to estimate the absorbed radiation dose in radiosensitive organs during coronary MDCT angiography using 320-MDCT and to determine the effects of tube voltage variation and heart rate (HR) control on absorbed radiation dose. MATERIALS AND METHODS Semiconductor field effect transistor detectors were used to measure absorbed radiation doses for the thyroid, midbreast, breast, and midlung in an anthropomorphic phantom at 100, 120, and 135 kVp at two different HRs of 60 and 75 beats per minute (bpm) with a scan field of view of 320 mm, 400 mA, 320 × 0.5 mm detectors, and 160 mm collimator width (160 mm range). The paired Students t test was used for data evaluation. RESULTS At 60 bpm, absorbed radiation doses for 100, 120, and 135 kVp were 13.41 ± 3.59, 21.7 ± 4.12, and 29.28 ± 5.17 mGy, respectively, for midbreast; 11.76 ± 0.58, 18.86 ± 1.06, and 24.82 ± 1.45 mGy, respectively, for breast; 12.19 ± 2.59, 19.09 ± 3.12, and 26.48 ± 5.0 mGy, respectively, for lung; and 0.37 ± 0.14, 0.69 ± 0.14, and 0.92 ± 0.2 mGy, respectively, for thyroid. Corresponding absorbed radiation doses for 75 bpm were 38.34 ± 2.02, 59.72 ± 3.13, and 77.8 ± 3.67 mGy for midbreast; 26.2 ± 1.74, 44 ± 1.11, and 52.84 ± 4.07 mGy for breast; 38.02 ± 1.58, 58.89 ± 1.68, and 78 ± 2.93 mGy for lung; and 0.79 ± 0.233, 1.04 ± 0.18, and 2.24 ± 0.52 mGy for thyroid. Absorbed radiation dose changes were significant for all organs for both tube voltage reductions as well as for HR control from 75 to 60 bpm at all tube voltage settings (p < 0.05). The absorbed radiation doses for the calcium score protocol were 11.2 ± 1.4 mGy for midbreast, 9.12 ± 0.48 mGy for breast, 10.36 ± 1.3 mGy for lung, and 0.4 ± 0.05 mGy for thyroid. CONCLUSION CT angiography with 320-MDCT scanners results in absorbed radiation doses in radiosensitive organs that compare favorably to those previously reported. Significant dose reductions can be achieved by tube voltage reductions and HR control.

Hypervascular Liver Lesions on MRI

T he superb liver-to-lesion contrast of MRI and its ability to display the same lesion enhancement patterns as CT combined with its lack of ionizing radiation have led to this modality being widely accepted for assessing the broad spectrum of hepatic abnormalities. Moreover, hepatocyte-specific contrast agents are now available. The differential diagnosis of hypervascular hepatic lesions depends on the status of the remainder of the organ. If the liver is normal, the most common causes of hypervascular liver lesions are hemangioma, focal nodular hyperplasia (FNH), adenoma, and hypervascular metastasis. In the presence of chronic liver disease, the likely causes include vascular shunts (transient hepatic enhancement difference [THED]), regenerative nodules, dysplastic nodules, and hepatocellular carcinoma (HCC) (Table 1).

Effect of Tube Voltage (100 vs. 120 kVp) on Radiation Dose and Image Quality using Prospective Gating 320 Row Multi-detector Computed Tomography Angiography.

Objectives: The objective of the following study is to evaluate the effect of reducing tube voltage from 120 to 100 kVp using prospective gating 320 row multi-detector computed tomography angiography on image quality and reduction in radiation dose. Materials and Methods: A total of 78 sequential patients were scanned with prospective electrocardiogram gating. A total of 45 patients (Group 1) with mean body mass index (BMI) 29 ± 2 and heart rate (HR) 57 ± 7 beats per minute (BPM) were scanned at 120 kVp. 33 patients (Group 2) with mean BMI 23 ± 3 and HR 58 ± 6 bpm were scanned at 100 kVp. Effective dose was calculated using dose length product and factor (k = 0.014). Quantitative assessment of image quality was calculated by measuring signal to noise ratio (SNR) and contrast to noise ratio (CNR) in the left ventricle and left main coronary artery. Two experienced cardiac radiologists using a three-point ordinal scale assessed subjectively image quality. Results: In Group 1, the median radiation dose was 5.31 mSv (95% confidence interval [CI]: 4.86-6.09) and for Group 2 (P = 0.009) the mean radiation dose was 3.71 mSv (95% CI: 2.76-4.87), representing 30% decrease in radiation dose. In multivariate analyses, adjusting for age, gender, HR, BMI, tube current and scan length, an absolute median reduction of 2.21 mSv (1.13-3.29 mSv) was noted in patients scanned with 100 kVp (P < 0.0001). The quantitative image quality (SNR and CNR) was not statistically significant between the groups. Subjective image quality was rated as good or excellent in 99% of coronary segments for both groups (P value was considered as non-significant). Conclusion: Our study suggests that radiation dose may be lowered from 120 to 100 kVp with preservation of image quality in patients whose BMI is ≤27.

Influence of Image Acquisition on Radiation Dose and Image Quality: Full versus Narrow Phase Window Acquisition Using 320 MDCT

Purpose. To compare radiation dose and image quality using predefined narrow phase window versus complete phase window with dose modulation during R-R using 320-row MDCTA. Methods. 114 patients underwent coronary CTA study using 320-row MDCT scanner. 87 patients with mean age (61 + 13 years), mean BMI (29 + 6), and mean heart rate (HR) (58 + 7 bpm) were imaged at predefined 66–80% R-R interval and then reconstructed at 75% while 27 patients with mean age (63 + 16 years), mean BMI (28 + 5), and mean HR (57 + 7 bpm) were scanned throughout the complete R-R interval with tube current modulation. The effective dose (ED) was calculated from dose length product (DLP) and conversion k (0.014 mSv/mGy/cm). Image quality was assessed using a three-point ordinal scale (1 = excellent, 2 = good, and 3 = nondiagnostic). Results. Both groups were statistically similar to each other with reference of HR (P = 0.59), BMI (P = 0.17), and tube current mAs (P = 0.68). The median radiation dose was significantly higher in those scanned with complete R-R phase window versus narrow phase window (P < 0.0001). Independently of patient and scan parameters, increased phase window was associated with higher radiation dose (P < 0.001). Image quality was better among those scanned with narrow phase window versus complete phase window (P < 0.0001). Conclusion. Our study supports that good HR control and predefined narrow window acquisition result in lower radiation dose without compromising diagnostic image quality for coronary disease evaluation.

Absorbed Radiation Dose in Radiosensitive Organs Using 64- and 320-Row Multidetector Computed Tomography: A Comparative Study

Aim. To determine absorbed radiation dose (ARD) in radiosensitive organs during prospective and full phase dose modulation using ECG-gated MDCTA scanner under 64- and 320-row detector modes. Methods. Female phantom was used to measure organ radiation dose. Five DP-3 radiation detectors were used to measure ARD to lungs, breast, and thyroid using the Aquilion ONE scanner in 64- and 320-row modes using both prospective and dose modulation in full phase acquisition. Five measurements were made using three tube voltages: 100, 120, and 135 kVp at 400 mA at heart rate (HR) of 60 and 75 bpm for each protocol. Mean acquisition was recorded in milligrays (mGy). Results. Mean ARD was less for 320-row versus 64-row mode for each imaging protocol. Prospective EKG-gated imaging protocol resulted in a statistically lower ARD using 320-row versus 64-row modes for midbreast (6.728 versus 19.687 mGy, P < 0.001), lung (6.102 versus 21.841 mGy, P < 0.001), and thyroid gland (0.208 versus 0.913 mGy; P < 0.001). Retrospective imaging using 320- versus 64-row modes showed lower ARD for midbreast (10.839 versus 43.169 mGy, P < 0.001), lung (8.848 versus 47.877 mGy, P < 0.001), and thyroid gland (0.057 versus 2.091 mGy; P < 0.001). ARD reduction was observed at lower kVp and heart rate. Conclusions. Dose reduction to radiosensitive organs is achieved using 320-row compared to 64-row modes for both prospective and retrospective gating, whereas 64-row mode is equivalent to the same model 64-row MDCT scanner.

Cancerogenesis Risks between 64 and 320 Row Detector CT for Coronary CTA Screening

Objectives: This study compares cancerogenesis risks posed by the 64 row detector and the 320 row detector computed tomography scanners used during coronary computed tomography angiography (CCTA) following decennial screening guidelines. Material and Methods: Data of the radiation absorbed after CCTA by lung, thyroid, and female breast in patients between 50 and 70 years of age obtained from prior published literature for the 64 row CT scanner were compared with data from our study using 320 row detector CT scanner. Data from the 64 row and the 320 row detector CT scanners was used to determine lifetime attributable risks (LAR) of cancer based on the biological effects of ionizing radiation (BEIR) VII report. Results: The relative reduction of LAR (%) for 50-, 60-, and 70-year-old patients undergoing scanning with the 320 row detector CT scanner was 30% lower for lung, and more than 50% lower for female breast when compared with results from 64 row detector CT scanner. The use of 320 row detector CT would result in a combined cumulative cancer incidence of less than 1/500 for breast in women and less than 1/1000 for lung in men; By comparison, this is much lower than other more common risk factors: 16-fold for lung cancer in persistent smokers, 2-fold for breast cancer with a first degree family member history of breast cancer, and 10-fold for thyroid cancer with a family member with thyroid cancer. Decennial screening would benefit at least 355,000 patients from sudden cardiac death each year, 94% of whom have significant coronary artery disease, with at least one stenosis >75%. LAR for thyroid cancer was negligible for both scanners. Conclusion: Lung and female breast LAR reductions with 320 row detector compared with 64 row detector CT are substantial, and the benefits would outweigh increased cancer risks with decennial screening in the age group of 50-70 years.