Prospective gating with 320-MDCT angiography: effect of volume scan length on radiation dose

Coronary Computer Tomography Angiography in 2021-Acquisition Protocols, Tips and Tricks and Heading beyond the Possible

Recent technological advances, together with an increasing body of evidence from randomized trials, have placed coronary computer tomography angiography (CCTA) in the center of the diagnostic workup of patients with coronary artery disease. The method was proven reliable in the diagnosis of relevant coronary artery stenosis. Furthermore, it can identify different stages of the atherosclerotic process, including early atherosclerotic changes of the coronary vessel wall, a quality not met by other non-invasive tests. In addition, newer computational software can measure the hemodynamic relevance (fractional flow reserve) of a certain stenosis. In addition, if required, information related to cardiac and valvular function can be provided with specific protocols. Importantly, recent trials have highlighted the prognostic relevance of CCTA in patients with coronary artery disease, which helped establishing CCTA as the first-line method for the diagnostic work-up of such patients in current guidelines. All this can be gathered in one relatively fast examination with minimal discomfort for the patient and, with newer machines, with very low radiation exposure. Herein, we provide an overview of the current technical aspects, indications, pitfalls, and new horizons with CCTA, providing examples from our own clinical practice.

Diagnostic performance and radiation dose of reduced vs. standard scan range abdominopelvic CT for evaluation of appendicitis

OBJECTIVE

To compare the diagnostic performance and radiation dose of reduced vs. standard scan range CT in diagnosing appendicitis.

METHODS

We retrospectively evaluated 531 consecutive adults who underwent emergency contrast-enhanced CT for abdominal pain or suspected appendicitis between July 2018 and March 2019. One hundred eighty-one young adults (mean age, 26 ± 6 years) were imaged from L2 to the symphysis pubis (reduced protocol). A total of 350 older patients (mean age, 55 ± 17 years) and those with a wider differential diagnosis were imaged from the diaphragm to the ischium (standard protocol). The reference standard was histopathology (surgical cases) or 3 months of medical record follow-up (nonsurgical cases). Sensitivity, specificity, and accuracy were calculated. Mean dose-length products (DLP) were compared (t-test). Using an anthropomorphic phantom, organ doses were measured on CT scanners with (scanner 1) and without (scanner 2) automatic voltage selection; effective radiation doses were calculated.

RESULTS

The frequency of appendicitis was 57/181 (31.5%) and 80/350 (22.9%) in the reduced and standard groups, respectively. Results of the reduced and standard protocols respectively were as follows (95% CI in parentheses): sensitivity, 98.2% (90.4-99.9%) and 100.0 (95.3-100.0%); specificity, 99.2% (95.6-100.0%) and 99.6% (97.9-100.0%); accuracy, 97.8% and 97.4%; mean DLPs, 363 ± 191mGy∙cm and 633 ± 591mGy∙cm (p < 0.0001). Phantom-based measurements of effective dose were 47% lower on scanner 1 (4.64 vs. 2.48 mSv) and 26% lower on scanner 2 (4.68 vs. 3.45 mSv) with the reduced protocol.

CONCLUSION

For young adults with clinically suspected appendicitis, a reduced scan range CT protocol is as sensitive, specific, and accurate as a standard scan range CT and imparts significantly less radiation dose.

KEY POINTS

• A reduced scan range CT protocol in young adults with high suspicion of appendicitis demonstrates similar diagnostic performance as a full-range abdominopelvic CT in undifferentiated adult patients. • The reduced scan range CT protocol imparts significantly less radiation dose: 57% based on dose-length product data and 26-47% based on anthropomorphic phantom data.

SCCT guidelines for the performance and acquisition of coronary computed tomographic angiography: A report of the society of Cardiovascular Computed Tomography Guidelines Committee: Endorsed by the North American Society for Cardiovascular Imaging (NASCI)

In response to recent technological advancements in acquisition techniques as well as a growing body of evidence regarding the optimal performance of coronary computed tomography angiography (coronary CTA), the Society of Cardiovascular Computed Tomography Guidelines Committee has produced this update to its previously established 2009 "Guidelines for the Performance of Coronary CTA" (1). The purpose of this document is to provide standards meant to ensure reliable practice methods and quality outcomes based on the best available data in order to improve the diagnostic care of patients. Society of Cardiovascular Computed Tomography Guidelines for the Interpretation is published separately (2). The Society of Cardiovascular Computed Tomography Guidelines Committee ensures compliance with all existing standards for the declaration of conflict of interest by all authors and reviewers for the purpose ofclarity and transparency.

Assessment of coronary in-stent restenosis: value of subtraction coronary computed tomography angiography

In conventional coronary computed tomography angiography (CCTA), metal artifacts are frequently observed where stents are located, making it difficult to evaluate in-stent restenosis. This study was conducted to investigate whether subtraction CCTA can improve diagnostic accuracy in the evaluation of in-stent restenosis. Subtraction CCTA was performed using 320-row CT in 398 patients with previously placed stents who were able to hold their breath for 25 s and in whom mid-diastolic prospective one-beat scanning was possible. Among these patients, 126 patients (94 men and 32 women, age 74 ± 8 years) with 370 stents who also underwent invasive coronary angiography (ICA) were selected as the subjects of this study. With ICA findings considered the gold standard, conventional CCTA was compared against subtraction CCTA to determine whether subtraction can improve diagnostic accuracy in the evaluation of in-stent restenosis. When non-assessable stents were considered to be stenotic, the diagnostic accuracy in the evaluation of in-stent restenosis was 62.7 % for conventional CCTA and 89.5 % for subtraction CCTA. When the non-assessable stents were considered to be non-stenotic the diagnostic accuracy was 90.3 % for conventional CCTA and 94.31 % for subtraction CCTA. When subtraction CCTA was used to evaluate only the 138 stents that were judged to be non-assessable by conventional CCTA, 116 of these stents were judged to be assessable, and the findings for 109 of them agreed with those obtained by ICA. Even for stents with an internal diameter of 2.5-3 mm, the lumen can be evaluated in more than 80 % of patients. Subtraction CCTA provides significantly higher diagnostic accuracy than conventional CCTA in the evaluation of in-stent restenosis.

Benefits of sonography in diagnosing suspected uncomplicated acute diverticulitis

OBJECTIVES

Despite evidence demonstrating equivalent accuracy of sonography and computed tomography (CT) in the workup of mild/uncomplicated acute diverticulitis, CT is overwhelmingly performed as the initial diagnostic test, particularly in the acute setting. Our study evaluated potential radiation and turnaround time savings associated with performing sonography instead of CT as the initial diagnostic examination in the workup of suspected uncomplicated acute diverticulitis.

METHODS

We retrospectively reviewed medical records from January 2010 to December 2012 for patients presenting with clinical symptoms of acute diverticulitis. Patients were categorized as a whole and subgrouped by age (>40 and <40 years). A modified Hinchey classification (Am Surg 1999; 65:632-636) was used to stage the severity of the disease. The effective radiation dose was calculated by multiplying the dose length product from the scanner by the standard conversion coefficient (k= 0.0021 mSv/mGy × cm). The turnaround time for patients was calculated as the time the examination was ordered by the emergency department physician or staff to the time the report was finalized.

RESULTS

Our study included 253 patients (172 male and 81 female; mean age ± SD, 50.2 ± 11.7 years; 132 >40 years and 121 <40 years). The distribution of patients by the modified Hinchey classification was 210 (stages 0 and 1a), 26 (stages 1b and 2), 17 (stages 3 and 4), 0 (fistula), and 0 (obstruction). The estimated CT radiation dose per patient was 21 ± 5.2 mSv. Mean turnaround times for CT and sonography were 138.5 ± 76.9 and 51.3 ± 44 minutes, respectively.

CONCLUSIONS

Sonography is a lower-cost, faster, and radiation-free alternative that measures up to the diagnostic standards of CT for management of suspected mild or uncomplicated acute diverticulitis.

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.

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 patient's whose BMI is ≤27.

Usefulness of dynamic volume scanning with 320-row CT in detecting recanalization of pulmonary arteriovenous fistula after coil embolization

Pulmonary arteriovenous fistula is a congenital and rarely acquired anomalous direct communications between pulmonary arteries and veins. Transcatheter embolization using metallic coil or detachable balloon is one of the common treatment procedure. However, recanalization after the embolization is one of the concern and its differentiation from the retrograde filling via pulmonary vein is difficult except using invasive angiography. We report a case with recanalized pulmonary arteriovenous fistula non-invasively detected by dynamic CT angiography with 320-rows multi detector CT.

A 45-year-old women who had underwent coil embolization for pulmonary arteriovenous fistula was examined with dynamic CT angiography and antegrade contrast enhancement of the fistula was noted. The recanalization through the embolized artery was confirmed by digital subtraction angiography, and the second coil embolization was performed. The follow-up dynamic CT angiography at three months after the second procedure found the retrograde enhancement of aneurysmal sac and no antegrade shunt. The dynamic CT angiography was useful for the detect the recanalization of pulmonary arteriovenous fistula.

Delayed pulmonary artery recanalization was reported to be observed in 5- 10% of cases as a complication after the successful occlusion of segmental pulmonary artery. Lack of change in aneurysmal diameter of pulmonary arteriovenous fistula demonstrated by CT was reported as the result of persistent aneurysmal perfusion or aneurysmal thrombosis. However, the retrograde filling of aneurysmal sac via pulmonary vein or remnant collateral pathway to the pulmonary arteriovenous fistula were also considered. Therefore, before the invasive procedure, we performed dynamic CT angiography to detect the flow direction and pathway to the pulmonary arteriovenous fistula. Using dynamic CT angiography, we could obtain hemodynamic information through the aneurysmal sac of pulmonary arteriovenous fistula and decide to proceed to the invasive embolotherapy. Prospective perfusion CT scan could be an alternative to invasive angiography in the initial follow-up after the embolotherapy or in the cases with the recanalization of pulmonary arteriovenous fistula.

Submillisievert median radiation dose for coronary angiography with a second-generation 320-detector row CT scanner in 107 consecutive patients

PURPOSE

To (a) use a new second-generation wide-volume 320-detector row computed tomographic (CT) scanner to explore optimization of radiation exposure in coronary CT angiography in an unselected and consecutive cohort of patients referred for clinical purposes and (b) compare estimated radiation exposure and image quality with that from a cohort of similar patients who underwent imaging with a previous first-generation CT system.

MATERIALS AND METHODS

The study was approved by the institutional review board, and all subjects provided written consent. Coronary CT angiography was performed in 107 consecutive patients with a new second-generation 320-detector row unit. Estimated radiation exposure and image quality were compared with those from 100 consecutive patients who underwent imaging with a previous first-generation scanner. Effective radiation dose was estimated by multiplying the dose-length product by an effective dose conversion factor of 0.014 mSv/mGy ⋅ cm and reported with size-specific dose estimates (SSDEs). Image quality was evaluated by two independent readers.

RESULTS

The mean age of the 107 patients was 55.4 years ± 12.0 (standard deviation); 57 patients (53.3%) were men. The median body mass index was 27.3 kg/m(2) (range, 18.1-47.2 kg/m(2)); however, 71 patients (66.4%) were overweight, obese, or morbidly obese. A tube potential of 100 kV was used in 97 patients (90.6%), single-volume acquisition was used in 104 (97.2%), and prospective electrocardiographic gating was used in 106 (99.1%). The mean heart rate was 57.1 beats per minute ± 11.2 (range, 34-96 beats per minute), which enabled single-heartbeat scans in 100 patients (93.4%). The median radiation dose was 0.93 mSv (interquartile range [IQR], 0.58-1.74 mSv) with the second-generation unit and 2.67 mSv (IQR, 1.68-4.00 mSv) with the first-generation unit (P < .0001). The median SSDE was 6.0 mGy (IQR, 4.1-10.0 mGy) with the second-generation unit and 13.2 mGy (IQR, 10.2-18.6 mGy) with the first-generation unit (P < .0001). Overall, the radiation dose was less than 0.5 mSv for 23 of the 107 CT angiography examinations (21.5%), less than 1 mSv for 58 (54.2%), and less than 4 mSv for 103 (96.3%). All studies were of diagnostic quality, with most having excellent image quality. Three of four image quality indexes were significantly better with the second-generation unit compared with the first-generation unit.

CONCLUSION

The combination of a gantry rotation time of 275 msec, wide volume coverage, iterative reconstruction, automated exposure control, and larger x-ray power generator of the second-generation CT scanner provides excellent image quality over a wide range of body sizes and heart rates at low radiation doses.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122621/-/DC1.

Comparison of coronary plaque subtypes in male and female patients using 320-row MDCTA

OBJECTIVE

Determine plaque subtype and volume difference in male and female patients with obstructive and non-obstructive CAD using 320-row MDCTA.

MATERIALS AND METHODS

128 patients with suspected CAD underwent MDCTA. All studies were divided into two groups based on disease severity. 0-70% stenosis (non-obstructive CAD) & >70% (obstructive). All were compared for plaque quantity and subtypes by gender. Main arteries, RCA, LM, LAD and LCX were analyzed using Vitrea 5.2 software to quantify fatty, fibrous and calcified plaque. Thresholds for coronary plaque quantification (volume in mm(3)) were preset at 35 ± 12 HU for fatty, 90 ± 24 HU for fibrous and >130 HU for calcified/mixed plaque and analyzed using STATA software.

RESULTS

Total plaque burden in 118 patients [65M: 53F] was significantly higher in all arteries in males compared to females with non-obstructive disease. Total plaque volume for males vs. females was: RCA: 10.10 ± 5.02 mm(3) vs. 6.89 ± 2.75 mm(3), respectively, p = 0.001; LAD: 7.21 ± 3.38 mm(3) vs. 5.89 ± 1.93 mm(3), respectively, p = 0.04; LCX: 9.13 ± 3.27 mm(3) vs. 7.16 ± 1.73 mm(3), respectively, p = 0.002; LM 15.13 ± 4.51 mm(3) vs. 11.85 ± 4.03 mm(3), respectively, p = 0.001. In sub-analyses, males had significantly more fibrous and fatty plaque in LM, LAD & LCX than females. However in the RCA, only fibrous plaque was significantly greater in males. Calcified plaque volume was not significantly different in both genders. Only 8% of patients had obstructive CAD (>70% stenosis); there was no significant difference in plaque volume or subtypes.

CONCLUSION

In patients with non-obstructive CAD, males were found to have significantly higher total coronary plaque volume with predominance of fibrous and fatty subtypes compared to females of the same age and BMI. There was no significant difference in plaque subtype or volume in patients with obstructive disease.

[Low dose cardiac computed tomography: how to obtain it?]

Since the introduction of Multi-slice computed tomography (CT), cardiac CT has been the increasingly used as a noninvasive modality for the diagnosis of coronary disease. Despite its potential benefits and promising clinical results, it has suffered from high doses of radiation associated with a risk of radiation-induced cancers. This has raised serious concerns in clinical practice. A number of strategies were then implemented to reduce the radiation dose associated with cardiac CT. The aim of this review is not to compare doses of different CT systems available on the market but to present an overview of different approaches to dose reduction and future directions.

State-of-the-art in CT hardware and scan modes for cardiovascular CT

Multidetector row computed tomography (CT) allows noninvasive anatomic and functional imaging of the heart, great vessels, and coronary arteries. In recent years, there have been several advances in CT hardware, which have expanded the clinical utility of CT for cardiovascular imaging; such advances are ongoing. This review article from the Society of Cardiovascular Computed Tomography Basic and Emerging Sciences and Technology Working Group summarizes the technical aspects of current state-of-the-art CT hardware and describes the scan modes this hardware supports for cardiovascular CT imaging.

Subtraction coronary CT angiography for calcified lesions

One of the main problems in coronary angiography using 64-row computed tomography (CT) is that the presence of severe calcification interferes with the assessment of lesions, which reduces diagnostic accuracy and may even make assessment of some coronary artery segments impossible. With 320-row CT, it is possible to avoid this problem by performing subtraction coronary CT, which fully exploits the performance capabilities of the CT system. However, subtraction coronary CT has several limitations. When these limitations have been overcome, this technique is expected to become a useful method for assessing patients with severe calcification and evaluating coronary artery stents.

Established and emerging dose reduction methods in cardiac computed tomography

Cardiac computed tomography (CT) is a non-invasive modality that is commonly used as an alternative to invasive coronary angiography for the investigation of coronary artery disease. The enthusiasm for this technology has been tempered by a growing appreciation of the potential risks of malignancy associated with the use of ionising radiation. In the spirit of minimizing patient risk, the medical profession and industry have worked hard to developed methods and protocols to reduce patient radiation exposure while maintaining excellent diagnostic accuracy. A complete understanding of radiation reduction techniques will allow clinicians to reduce patient risk while providing an important diagnostic service. This review will consider the established and emerging techniques that may be adopted to reduce patient absorbed doses from x-ray CT. By modifying (1) x-ray tube output, (2) imaging time (scan duration), (3) imaging distance (scan length) and (4) the appropriate use of shielding, clinicians will be able to adhere to the 'as low as reasonably achievable (ALARA)' principle.