Eur Radiol DOI 10.1007/s00330-017-4888-7
ONCOLOGY
Improved assessment of mediastinal and pulmonary pathologies in combined staging CT examinations using a fast-speed acquisition dual-source CT protocol Franziska M. Braun 1 & Veronica Holzner 1 & Felix G. Meinel 1 & Marco Armbruster 1 & Martina Brandlhuber 1 & Birgit Ertl-Wagner 1 & Wieland H. Sommer 1
Received: 6 September 2016 / Revised: 17 April 2017 / Accepted: 11 May 2017 # European Society of Radiology 2017
Abstract Objectives To demonstrate the feasibility of fast Dual-Source CT (DSCT) and to evaluate the clinical utility in chest/abdomen/pelvis staging CT studies. Methods 45 cancer patients with two follow-up combined chest/abdomen/pelvis staging CT examinations (maximally ±10 kV difference in tube potential) were included. The first scan had to be performed with our standard protocol (fixed pitch 0.6), the second one using a novel fast-speed DSCT protocol (fixed pitch 1.55). Effective doses (ED) were calculated, noise measurements performed. Scan times were compared, motion artefacts and the diagnostic confidence rated in consensus reading. Results ED for the standard and fast-speed scans was 9.1 (7.011.1) mSv and 9.2 (7.4-12.8) mSv, respectively (P = 0.075). Image noise was comparable (abdomen; all P > 0.05) or reduced for fast-speed CTs (trachea, P = 0.001; ascending aorta, P < 0.001). Motion artefacts of the heart/the ascending aorta (all P < 0.001) and breathing artefacts (P < 0.031) were reduced in fast DSCT. The diagnostic confidence for the evaluation of mediastinal (P < 0.001) and pulmonary (P = 0.008) pathologies was improved for fast DSCT. Conclusions Fast DSCT for chest/abdomen/pelvis staging CT examinations is performed within 2 seconds scan time and eliminates relevant intrathoracic motion/breathing artefacts. Mediastinal/pulmonary pathologies can thus be assessed with high diagnostic confidence. Abdominal image quality remains excellent.
* Franziska M. Braun
[email protected]
1
Institute for Clinical Radiology, University Hospital Munich, Marchioninistraße 15, 81377 Munich, Germany
Key points • Fast dual-source CT provides chest/abdomen/pelvis staging examinations within 2 seconds scan time. • The sevenfold scan time reduction eliminates relevant intrathoracic motion/breathing artefacts. • Mediastinal/pulmonary pathologies can now be assessed with high diagnostic confidence. • The coverage of the peripheral soft tissues is comparable to single-source CT. • Fast and large-volume oncologic DSCT can be performed with 9 mSv effective dose. Keywords Dual-source computed tomography . Oncology . Thorax . Abdomen . Pelvis
Abbreviations CT Computed tomography CTDIvol Volumetric CT dose index DLP Dose length product DSCT Dual-source CT system ED Effective radiation dose FOV Field of view PACS Picture archiving and communication system ROI Region of interest
Introduction Modern imaging techniques, predominantly computed tomography (CT), play an important role in the management of oncological diseases: they are intensively used for the diagnosis, staging, evaluation of treatment response and active surveillance for disease recurrence [1]. Oncologic imaging usually requires large scan volumes as metastatic spread
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may occur in very distant body areas. However, the image quality of large-volume staging CT scans is often hampered by aortic/cardiac motion artefacts as well as by breathing artefacts that compromise the evaluation of the mediastinal structures and the lungs. Our hypothesis was that thirdgeneration Dual-Source CT (DSCT) offers new technical solutions that may improve the image quality of large-volume staging CT examinations. A DSCT scanner provides two acquisition systems mounted on the CT gantry with an angular offset of 90° [2]. Each acquisition system consists of a tube-detector pair. Tube voltage and tube current can be determined independently for both tube-detector pairs, which allows for different scanning modes: a single-source, a single-energy and dual-source (Bdual-source CT^), and a dual-energy and dual-source mode (Bdual-energy CT^). Scanning with two acquisition systems has been shown to offer different advantages: First, the exposure time is decreased by a factor of 2, with a consecutive temporal resolution of one quarter of the gantry rotation time. Secondly, the dual-source technique provides so-called Bhighpitch modes^ for fast spiral CT examinations [2]. It is well known that single-source CT is characterised by undersampling of data at pitch factors larger than 1.5. The second measurement system in DSCT allows for a gapless zsampling at pitch factors even larger than 3, depending on the required final scan field of view (FOV) [2]. The gapless data sampling at pitch factors of about 3 is limited to the FOV of detector B, which is – for system geometry – considerably smaller than the typical 500-mm-measurement-field of detector A. High-pitch DSCT has been widely shown to improve cardiovascular CT imaging [3–7] and to avoid relevant motion artefacts in chest CT imaging [8–10]. In their review, Simons et al. gave an overview about the role of dual-energy CT for oncologic imaging [11]. There are former studies that evaluated high-pitch DSCT for the acquisition of combined chest/ abdomen and combined abdomen/pelvis staging DSCT examinations, respectively. They demonstrated, that high-pitch DSCT allows for radiation dose reduction while preserving a good objective as well as subjective image quality [12, 13]. However, up to the second-generation DSCT scanners, one limitation of high-pitch DSCT scanning of large body areas was the small final FOV at increasing pitch values. The thirdgeneration DSCT system delivers higher (2 × 120 kW) generator power [14], pitch factors up to 3.2, a rotation speed of 0.25 s and a broader detector coverage (number of simultaneously acquired slices 2 × 192) and consecutively promises bigger final FOV in high-pitch and large-volume DSCT. The aim of this study was to demonstrate the feasibility of fast third-generation DSCT and to evaluate the clinical utility in large-volume chest/abdomen/pelvis staging CT studies. To address this purpose, we compared radiation dose metrics, noise measurements and scan times between our standard
and a novel fast DSCT protocol. A consensus reading was performed to assess the subjective image quality and to determine the incidence of motion artefacts for both datasets.
Materials and methods Patient selection and study design The study was conducted as a retrospective, single-centre study. The study protocol was approved by the responsible institutional review board with waiver of informed consent. Forty-five patients with known malignancies were included in this study. All patients had been referred to our department for clinically indicated oncological staging CT examinations of the chest, abdomen and pelvis between June 2011 and March 2014. Inclusion criteria were two follow-up staging CT examinations of the chest/abdomen/pelvis, with the first scan having been performed using our standard protocol of a second-generation DSCT scanner (fixed pitch 0.6; SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany) and the second one using the novel high-pitch protocol (fixed pitch 1.55) of a third-generation DSCT machine (SOMATOM Force, Siemens Healthcare, Forchheim, Germany). The study was designed to specifically evaluate the effect of fast-speed image acquisition on image quality and radiation dose. To minimise the confounding effect of potential differences in tube voltage selection, we excluded patients with a >10 kV difference in tube potential between both examinations from the analysis in order to avoid the influence of large kV differences on subjective and objective image quality measurements. CT acquisition protocol and image reconstruction CT acquisition parameters for the standard and the fast-speed acquisition protocol are summarised in Table 1. In all patients, the scan range covered the entire pulmonary parenchyma and the whole abdominal region, extending from the pulmonary apex to the lowest part of the pelvis. Patients were asked to hold their breath in deep inspiration during the examination. Images were obtained 70 s after intravenous injection of the non-ionic contrast agent Iomeron® 400 (Bracco Diagnostics, Milan, Italy). Contrast volume was adapted to body weight with a volume of 1.5 ml per kg body weight. For both DSCT systems, lung and abdominal image series were reconstructed with a slice thickness of 5 mm and an increment of 5 mm. Corresponding kernels of I30 and Br36 were used for the third-generation and the second-generation DSCT system, respectively. An intermediate iterative reconstruction strength of 3 was used for all reconstructions on both CT systems.
Eur Radiol Table 1 Acquisition parameters DSCT system kV (range) Effective mAs (range) Rotation time Section thickness Detector rows Pitch
Control group
Fast-speed acquisition group
Second generation DSCT 100 – 140
Third generation DSCT 90 – 130
85 – 368
148 – 398
0.5 s 0.6 mm
0.25 s 0.6 mm
128 0.6
192 1.55
Acquisition parameters for our standard (control group) and the novel fast-speed acquisition mode (fast-speed acquisition group) are presented. DSCT Dual-source CT system
Radiation metrics The volume CT dose indices (CTDIvol) and dose length products (DLP) were retrieved from the patient dose report in the picture archiving and communication system (PACS, Syngo Imaging 2010, Siemens Healthcare). Effective radiation doses were estimated by multiplying the DLP with a standard conversion factor for adult abdomen CT of 0.0153 mSv/ mGy*cm [15]. Estimation of scanning time The scanning time was determined by the period of time between the first and the lastly acquired image in the z-axis of the reconstructed axial images. Analysis of the objective image quality Quantitative analysis of image quality was performed to determine and compare image noise between the two different acquisition protocols. Image noise was measured by manually placing circular regions of interest (ROI) with a standardised size of 1 cm2 on axial slices within six different body regions: the air inside the trachea and the extrathoracic air at a z-axis position 1 cm above the tracheal bifurcation, the ascending aorta (two measurements with a distance of 2 cm), the liver parenchyma (four measurements within different segments), the retroperitoneal fat (one measurement on each side) and the paraspinal muscles (one measurement on each side), respectively (see also Fig. 1). For each region, the values were summarised and the arithmetic mean was calculated. The standard deviation (SD) of the CT attenuation within the regions of interest was defined as image noise. Furthermore, all CT datasets were analysed with regard to a complete/incomplete depiction of the intrathoracic and intraabdominal organs as well as the coverage of the patients’ peripheral soft tissues.
Subjective assessment of the diagnostic confidence and of motion artefacts Two readers (with 8 and 3 years of experience in oncologic imaging, respectively) blinded to the DSCT scanner, the acquisition protocol and the patients’ identifying information, rated their diagnostic confidence for the evaluation of mediastinal abnormalities (e.g., mediastinal lymph-adenopathy), overall pulmonary as well as overall abdominal image quality in consensus reading. Furthermore, they assessed motion artefacts of the heart and of the ascending aorta, as well as breathing artefacts. For this purpose, the anonymised data sets from the two different acquisition protocols (with all image text hidden) were presented in a random order that had been defined by a third person not involved in the image quality analysis. The lung parenchyma as well as heart motion and breathing artefacts were assessed in a lung tissue window preset (window level, -600 HU; width, 1600 HU). The mediastinum and the abdominal structures, as well as motion artefacts of the ascending aorta were assessed in a soft tissue window preset (window level, 40 HU; width, 300 HU). The subjective assessment of the diagnostic confidence for the evaluation of pulmonary, mediastinal and abdominal pathologies (primary malignancies, lymphogenic/haematogenic metastatic spread, associated pathologies) was rated on a fourpoint Likert scale: ^not confident^, Bpoorly confident^, Bquite confident^ or Bhighly confidentB. The term Bdiagnostic confidence^ refers to the confidence in confirming or excluding a pathology with the given image quality, regardless of whether a patient had a specific pathology or not. The fourpoint scale represents a spectrum of different degrees of certainty: from Bhigh confidence^, where the image quality was excellent and the readers could make a definitive decision to Bnot confident^, where the image quality was strongly impaired so that a reliable decision was not possible to make. Figure 2 illustrates the subjective rating scale using the example of the mediastinum. Motion artefacts were classified as Bnot present^, Bminor^ or Bmajor^. Minor artefacts were defined as not relevant for the diagnostic confidence, whereas major artefacts were
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Fig. 1 Summary figure with exemplary axial CT slices of each body area in which ROI (region of interest) measurements had been performed. Image noise was measured by manually placing circular regions of interest with a standardised size of 1 cm2 on axial slices within six different body regions (white circles): the air inside the trachea (A), the extrathoracic air at a z-axis position 1 cm above the tracheal bifurcation (B), the ascending aorta (two measurements with a distance of 2 cm) (C),
the liver parenchyma (four measurements within different segments) (D), the retroperitoneal fat (one measurement on each side) (E) and the paraspinal muscles (one measurement on each side) (F), respectively. The standard deviation (SD) of the CT attenuation within the ROI was defined as image noise. The values were summarised for each region and the arithmetic mean calculated
defined as substantial artefacts hampering the diagnostic evaluation of the affected areas.
Belgium). Binary data was displayed as absolute frequencies and proportions. Continuous data were tested for a normal distribution using the Kolmogorov-Smirnov test. Paired samples t-test was used to compare normally distributed parameters (e.g., patient characteristics), while the Wilcoxon test for paired samples was used to compare data, for which normal distribution had been rejected (e.g.,radiation metrics, scanning time and objective image quality). Normally distributed,
Statistical analysis Statistical analysis was performed using MedCalc for Windows, version 12.5 (MedCalc Software, Ostend,
Fig. 2 Figure 2 illustrates the four-point Likert scale of the subjective image quality reading using the example of the mediastinum. Image examples are given for Bhigh confidence^ (A), Bquite confident^ (B) and Bpoor confidence^ (C). BNot confident^ did not occur in our study. In case of Bhigh confidence^ (A) there is excellent image quality. The small mestiastinal mass can be diagnosed to be a small serous fluid collection within the anterior portion of the superior aortic recess. In case
of Bpoor confidence^ (C), the image quality is markedly impaired (especially by major motion artefacts) so that the etiology of the small mass can only be estimated from its location. A small fluid collection seems to be Bpossible^. BQuite confident^ (B) means, that the image quality is only slightly impaired (e. g., by minor motion artefacts) so that a small fluid collection remains Bprobable^
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continuous data were displayed as mean and standard deviation, not-normally distributed, continuous data as median and interquartile range. TheWilcoxon test for paired samples was also used to compare the results of the subjective image quality reading. P-values < 0.05 were considered to indicate statistical significance.
Results
standard protocol and 9.2 mSv (7.4-12.8) for the fast-speed acquisition mode (P = 0.075). Scanning time Using our standard protocol, the median scanning time was 14.0 s (13.0-14.0). Using the novel fast-speed acquisition mode of the third-generation DSCT scanner, the median scanning time was reduced to 2.0 s (1.0-2.0) (P < 0.001). Objective image quality: Noise measurements and coverage of the patients’ diameter
Patient characteristics Our patient cohort consisted of 28 men and 17 women with a mean age of 63 ± 12 years. The average time interval between the follow-up CT examinations was 247 ± 211 days. For each patient, the body mass indices (BMIs) were calculated using the recorded body height and weight. With a mean BMI of 24.3 ± 4.8 kg m-2 at the first examination time point versus 24.2 ± 5,0 kg m-2 at the second appointment, no significant change concerning BMI values was noted (P = 0.718). The three most frequently observed primary malignancies in our study cohort were renal cell carcinoma (12 cases), different subtypes of sarcoma (nine cases) and colorectal cancer (five cases). The remaining patients suffered from urothelial cell carcinoma, lymphoma, oesophageal, gastric or pancreatic cancer (two cases each), adrenal carcinoma, lung, breast, ovarian or endometrial cancer, cholangiocellular carcinoma, seminoma, malignant epithelioid hemangioendothelioma and myeloproliferative neoplasm (one case each).
Radiation dose Median CTDIvol was 8.5 mGy (6.9-10.9) for CT examinations acquired with our standard protocol, and 8.7 mGy (7.3-12.2) for CT scans performed with the novel fast-speed acquisition protocol of the third-generation DSCT machine (P = 0.135). Corresponding median DLP values were 592.0 mGy*cm (455.0-727.0) and 603.6 mGy*cm (482.9-833.4), respectively (P = 0.075). Median ED were 9.1 mSv (7.0-11.1) for the
Image noise measurements are summarised in Table 2. Using the fast-speed acquisition protocol, image noise was significantly reduced within the following two regions: the lumen of the trachea and the lumen of the ascending aorta (all P ≤ 0.001). In the remaining regions, which are listed in Table 2, no statistically significant differences were found (all P > 0.05). The intrathoracic/ intraabdominal organs were completely depicted in all CT scans for both the standard and the fast DSCT protocol. In 29% and 31%, respectively, there was a slight and comparably incomplete coverage of the peripheral soft tissues with regard to the skin and the subcutaneous tissue only at the level of the pelvis. Subjective assessment of the diagnostic confidence and of motion artefacts Table 3 summarises the distribution of the diagnostic confidence ratings. The diagnostic confidence for the assessment of mediastinal abnormalities (P < 0.001) and pulmonary pathologies (P = 0.008) was significantly better for the fast-speed than for our standard protocol. No statistically significant difference was noted for the assessment of the abdominal structures (P > 0.05). The distribution of the motion artefacts ratings for both acquisition modes is shown in Table 4. Using the standard protocol, 47% of the examinations displayed major cardiac
Table 2 Objective image quality Extrathoracic Air Trachea Aorta ascendens Liver Retroperitoneal Fat Paraspinal Muscles
Control group
Fast-speed acquisition group
P-Value
5.0 HU (4.0 – 5.0) 11.0 HU (9.0 – 13.0) 9.0 HU (7.5 – 11.1) 9.5 HU (9.0 – 10.8) 11.0 HU (10.0 – 13.5) 11.5 HU (9.5 – 13.0)
4.0 HU (4.0 – 5.0) 9.0 HU (7.0 – 11.3) 6.5 HU (5.5 – 8.0) 10.0 HU (8.4 – 11.5) 11.7 HU (10.5 – 14.5) 12.0 HU (9.9 – 14.0)
P = 0.164 P = 0.001 P < 0.001 P = 0.246 P = 0.266 P = 0.219
Image noise as a parameter of the objective image quality was measured within different body regions. The standard deviation of the CT attenuation within the region of interest was defined as image noise. The results are displayed as median and interquartile range in parenthesis. Wilcoxon test was used for statistical analysis
Eur Radiol Table 3 Subjective assessment of diagnostic confidence
Control group
Fast-speed acquisition group
High confidence
36
44
Quite confident Poor confidence
7 2
1 0
High confidence
2
34
Quite confident Poor confidence
23 20
11 0
38
39
7
6
Overall pulmonary image quality
P-Value P = 0.008
Mediastinal pathologies
P < 0.001
Overall abdominal image quality High confidence
P > 0.05
Quite confident
Image quality was rated by two experienced readers in consensus reading, using a four-point Likert scale (Bnot confident^, Bpoorly confident^, Bquite confident^ and Bhighly confident^). In cases of Bhigh confidence^ the image quality was excellent and the readers could make a definitive decision. When image quality was not perfect and the decision Bprobable^, the readers rated to be Bquite confident^. BPoor confidence^ means that image quality was markedly reduced, so that the presence/absence of pathologies was only Bpossible^. Our study did not reveal any cases with Bnot confident^ (image quality strongly impaired so that a reliable decision is not possible to make). Data are shown as absolute frequencies. Wilcoxon test for paired samples was used to compare the diagnostic confidence ratings between our standard and the fast-speed acquisition protocols
motion artefacts and 53% minor ones. Also, 64% of the scans showed major motion artefacts and 13% revealed minor motion artefacts of the ascending aorta. Major breathing artefacts occurred in 4% and minor breathing artefacts in 9%. Using the fast-speed acquisition mode, 2% of the scans were rated to show major cardiac motion artefacts and 20% minor ones. In addition, 15% of the examinations displayed major motion artefacts of the ascending aorta and 59% minor ones. No breathing artefacts were observed. Hence, the percentage of cardiac motion artefacts (P < 0.001), of motion
artefacts of the ascending aorta (P < 0.001), and of breathing artefacts (P = 0.031) was significantly lower for CT examinations acquired with the fast-speed than for those acquired with our standard protocol. Image examples for the elimination of breathing artefacts in fast and large-volume DSCT of the chest/abdomen/pelvis are given in Figs. 3 and 4 (case of severe dyspnea). Figures 5 and 6 give various image examples for the significant aortic/ cardiac motion artefact reduction within the mediastinum using fast DSCT.
Table 4 Motion artefacts Control group Heart motion artefacts Major Minor None Motion artefacts of the ascending aorta Major Minor None Breathing artefacts Major Minor None
Fast-speed acquisition group
P-Value P < 0.001
21 24 0
1 7 36
39 6 0
7 22 26
2 4 0
0 0 45
P < 0.001
P = 0.031
Images were analysed with regard to motion artefacts of the heart, motion artefacts of the ascending aorta and breathing artefacts. Images were rated to display Bno artefact^, or to exhibit Bminor^ or Bmajor^ artefacts, respectively. Results are given as absolute frequencies for the standard and the fast-speed acquisition protocol. Wilcoxon test for paired samples was used to test for statistical significance
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Fig. 3 A 53-year-old male patient with esophageal cancer. The fastspeed acquisition mode resulted in a high diagnostic confidence for the assessment of the basal lungs (C, D), compared to only a poor confidence (A, B) for the examination performed with our standard protocol. Even if the position of the patient slightly differs between the two scans, the coronal images clearly demonstrate major breathing artefacts in the basal lungs in the standard CT scan (A, B), whereas the fast-speed CT scan is motion artefact free. In this case, also the image quality of the diaphragmatic region was affected by breathing artefacts in standard CT (A, B)
Discussion This study aimed to evaluate the feasibility and the clinical utility of fast and large-volume Dual-source CT (DSCT) examinations in oncologic imaging. Our study results demonstrate some major advantages of a novel fast-speed acquisition DSCT protocol for combined chest/abdomen/pelvis CT scans that have important clinical implications. While preserving the high abdominal image quality known from the standard protocol, the fast-speed acquisition mode allowed for a significant aortic/cardiac motion artefact reduction and for the elimination of any breathing artefacts within the lungs. The diagnostic confidence for the evaluation of pulmonary and
mediastinal pathologies was rated to be significantly higher in fast DSCT scans than in standard CT. The abdominal image quality remained excellent. Even though fast DSCT resulted in image quality optimization, it did not require additional radiation dose when compared to our standard protocol. The novel fast DSCT protocol was initially implemented in such a way as to achieve comparable radiation dose levels as provided by our standard protocol. With median effective doses of approximately 9 mSv, the radiation dose level of our standard protocol already fell considerably below the common value of 17 mSv reported in the literature [16, 17]. Thus, not radiation dose reduction but further image quality optimization was the primary objective of the novel protocol. As already mentioned above, there are former studies that evaluated high-pitch protocols for the acquisition of combined chest/abdomen CT or combined abdomen/pelvic CT examinations for second-generation DSCT machines. Both of them reported a benefit for high-pitch DSCT imaging, as it allowed for a substantial radiation dose reduction while preserving a good objective and subjective image quality [12, 13]. However, up to the second-generation DSCT scanners, one limitation of high-pitch DSCT scanning of large body areas was the small final FOV with an incomplete transversal depiction of the patient at increasing pitch values. Also our standard protocol using the second-generation DSCT machine worked in single-source mode with low pitch values in order not to risk an incomplete coverage of the patients’ periphery. Because of the higher generator power of the third-generation DSCT scanner, we increased the applied pitch value from 0.6 to 1.55 using a single-energy, dual-source acquisition mode. Together with an elevated rotation speed of 0.25 s and a broader detector coverage, we expected to implement a dose-neutral, fast-speed acquisition protocol for large-volume scanning that is less affected by the limited FOV known from second-generation DSCT imaging. With median effective doses of approximately 9 mSv, the radiation dose levels of both protocols were statistically comparable. At the same time, we observed a substantial scan time reduction of about 86% from 14.0 s for the standard to 2.0 s for the fastspeed CT scans. This marked acceleration of image acquisition has to be considered as the combined result of the increased pitch factor, the broader detector coverage, the shorter rotation time of the third-generation DSCT system and the high temporal resolution provided by the dual-source acquisition mode. The substantial scan time reduction lead to a significant reduction of aortic/ heart motion artefacts and to the elimination of breathing artefacts within the lungs in our cohort examined with the fast DSCT protocol. The subjective assessment of the diagnostic confidence for theevaluationofmediastinalandpulmonarypathologiesrevealed significantly better results for the fast DSCT protocol, while it was comparable on the level of the abdomen. This finding can be attributed to the described motion artefact reduction as well as the significant image noise reduction within the mediastinum and the basal lungs. The benefit from fast image acquisition on motion artefact reduction and consecutive image quality
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Fig. 4 Figure 3 demonstrates the effect of motion artefact reduction/ breathing artefact elimination in fast DSCT even in case of severe dyspnea: 81-year-old male patient with adrenal cancer of the left adrenal gland and tumour invasion of the vena cava inferior (A). There was continuous tumour expansion into the right atrium (B). Initial staging was performed with the fast DSCT protocol. The respective chest images were motion and breathing artefact free and did not reveal any lung nodules (C). Three weeks after adrenalectomy with resection of the intravenous tumour thrombus a chest/ abdomen/ pelvic CT using our standard protocol was performed because of a decreasing alertness and
signs of infection. The patient suffered from considerable dyspnea. The respective chest images revealed pleural effusions and an impaired ventilation of the basal bronchopulmonary segments. There are major breathing artefacts in both lungs that would render staging purposes impossible (D). One week later, a second postoperative scan was performed, this time with the fast DSCT protocol (E). On the level of the chest, the dyspneic patient still suffered from pleural effusions and an impaired ventilation of the adjacent lung tissue. Fast DSCT did not reveal any breathing artefacts. Neither there were any motion artefacts of the ascending aorta and the heart
optimization has already been demonstrated for other body areas and protocols, respectively. Farshad-Ambacker showed in a phantom study, that high-pitch DSCTimaging led to a significantly decreased percentage of motion artefacts in a chest/cardiac phantom and consecutively to an improved image quality [18]. Christensen et al. recently demonstrated, that high-pitch DSCT computed tomography angiography significantly decreased motion artefacts of the ascending aorta, when compared to singlesource, standard-pitch techniques [19]. In our opinion, the improved mediastinal and pulmonary image quality of large-volume chest/abdomen/pelvis staging CT examinations has important clinical implications: advanced cancer is often accompanied by pulmonary metastatic spread as well as mediastinal lymphadenopathy. These pathologies are preferably assessed in chest CT imaging. However, image quality of the mediastinum and the lungs is often hampered by motion and breathing artefacts in large-volume scans. Due to the underlying malignant disease or as a consequence of the treatment-associated immunosuppression, cancer patients often suffer from associated thoracic or abdominal pathologies, which cause dyspnoea and compromise the patients’ capability to hold the breath during image acquisition (e.g., pneumonia, pleural carcinosis, pleural effusion, ascites, etc.). Using the novel fast third-generation DSCT protocol, combined staging CT examinations of the chest/abdomen/pelvis can now be performed within only 2 s. Thus, relevant
breathing artefacts are unlikely to occur even in patients with severe dyspnea (as shown in our image material). Another objective of investigation in our study was the coverage of the patients’ body periphery using the fast DSCT procotol in large-volume staging CT imaging. The analysis of the CT images revealed, that there was a very slight incomplete depiction of the subcutanous fat tissue and the skin in about one third of the standard CT scans and the fast DSCT examinations, too. The intrathoracic/intraabdominal organs were completely depicted in all CT scans for our standard protocol and for the fast DSCT protocol. Peripheral information loss always occurred at the level of the pelvis. This can be explained by the patients’ anatomy in most cases. Due to the advanced patients’ age and the underlying malignant diseases, the tension of the connective tissue seemed to be reduced. This led to an increased patient diameter at the level of the pelvis in supine position. In several cases, there was a slight eccentric patient position, which might also partially explain this percentage. In the end, fast and large-volume DSCT provides comparable information with regard to the patients’ peripheral soft tissues as single-source CT. Obviously, in question of oncologic imaging information loss even of peripheral soft tissues cannot be estimated to marginal. Special attention in case of soft-tissue metastases should be payed to melanoma, carcinomas of lung, breast, kidney or colon and less mentioned locations of primary tumour.
Eur Radiol Fig. 5 The fast-speed acquisition mode allowed for a substantial motion artefact reduction of the aorta and the heart, which is shown for three different patients: An 80-year-old female patient with urothelial cell carcinoma (A and B), an 45-year-old male patient with sigmoid colon cancer (C and D) and an 72-year-old male patient with renal cell carcinoma. Axial view demonstrates better image quality of the mediastinum in dual-source CT examinations performed with the fast-speed acquisition protocol (A, C, E) when compared to our standard-pitch protocol (B, D, F)
Fig. 6 The significant motion artefact reduction within the mediastinum using fast DSCT facilitates the evaluation of mediastinal pathologies, especially of a mediastinal lymphadenopathy. Figure 5 shows the consecutive staging CT scans of a 50-year-old female patient with lymphoma (A, B) and of a 69-year-old female patient with liposarcoma (C, D). The first examinations had been performed with the standard protocol (A, C), the following ones with the fast DSCT protocol (B, D). In both cases, the staging CT examinations revealed multiple lesions within the mediastinum. Due to the motion artefacts and the blurred margins of these lesions in standard CT, the etiology of these masses
remained unclear and a malignant mediastinal lymphadenopathy could not be excluded (A, C). In fast DSCT, the lesions revealed to be serous fluid collections within the pericardial cavity (anterior portion of the superior aortic recess and left pulmonary recess of the transverse sinus) (B, D) and small lymph nodes within the aortopulmonary window (B). Enlarged lymph nodes with signs of malignant transformation were excluded. The posterior portion of the superior aortic recess, which is almost not affected by motion artefacts on standard CT, did not contain any obscurations in our image examples
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Some limitations regarding our study design merit consideration. First, we used a retrospective study design. However, the non-randomized nature of retrospective studies is less problematic in this case, since we compared two examinations performed in the identical patient population, which allowed for an intra-individual comparison of the two DSCT techniques. Secondly, we only assessed the diagnostic confidence, not the diagnostic accuracy of the novel fast DSCT protocol. The subjective image quality rating wasperformedbyonlytworadiologistsinconsensusreading.They were blinded to the DSCTscanner, the acquisition protocol and all patients’ identifying information. However, we cannot exclude potential bias resulting from the familiarity of the readers with the technical equipment of their radiologic institute. In our study, we did not compare the final FOV values, but analysed the image data sets with regard to a complete/incomplete depiction of the patients’ diameter. In future studies, the absolute FOV values should be recorded, too. Finally, with 45 consecutive patients, our study cohort was relatively small. Thus, further studies with a prospective study design, a bigger study cohort and a diagnostic accuracy endpoint should be performed in the near future. Summing up, our study showed some major advantages of fast DSCT in large-volume staging CT that are crucial for qualitative oncologic imaging: the sevenfold scan time reduction to only 2 seconds led to the elimination of relevant aortic/ cardiac motion artefacts and of any breathing artefacts from fast DSCT scans. Mediastinal/pulmonary pathologies can now be assessed with high diagnostic confidence. The abdominal image quality remained excellent. Finally, the novel fast DSCT protocol provided a similar depiction of the patients’ peripheral soft tissues as our standard protocol, without additional peripheral information loss as formerly known from second-generation high-pitch DSCT.
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Compliance with ethical standards Guarantor Sommer.
The scientific guarantor of this publication is W. H.
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14. Conflict of interest The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article. 15. Funding The authors state that this work has not received any funding. Statistics and biometry No complex statistical methods were necessary for this paper. Informed consent Written informed consent was waived by the Institutional Review Board.
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18. Ethical approval Institutional Review Board approval was obtained. Methodology • retrospective • diagnostic study • performed at one institution
19.
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