[German Radiological Society and the Professional Association of German Radiologists position paper on coronary computed tomography: clinical evidence and quality of patient care in chronic coronary syndrome]. / Positionspapier von DRG und BDR zur Computertomographie des Herzens: Klinische Evidenz und Versorgungsqualität beim chronischen Koronarsyndrom.

This position paper is a joint statement of the German Radiological Society (DRG) and the Professional Association of German Radiologists (BDR), which reflects the current state of knowledge about coronary computed tomography (CT). It is based on preclinical and clinical studies that have investigated the clinical relevance as well as the technical requirements and fundamentals of cardiac computed tomography.

Comparison of volumetric and functional parameters in simultaneous cardiac PET/MR: feasibility of volumetric assessment with residual activity from prior PET/CT.

OBJECTIVE: To compare cardiac left ventricular (LV) parameters in simultaneously acquired hybrid fluorine-18-fluorodeoxyglucose ([18F] FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) in patients with residual tracer activity of upstream PET/CT. METHODS: Twenty-nine patients (23 men, age 58±17 years) underwent cardiac PET/MRI either directly after a non-cardiac PET/CT with homogenous cardiac [18F] FDG uptake (n=20) or for viability assessment (n=9). Gated cardiac [18F] FDG PET and cine MR sequences were acquired simultaneously and evaluated blinded to the cross-imaging results. Image quality (IQ), end-diastolic (LVEDV), end-systolic volume (LVESV), ejection fraction (LVEF) and myocardial mass (LVMM) were measured. Pearson correlation and intraclass correlation coefficient (ICC), regression and a Bland-Altman analysis were assessed. RESULTS: Except LVMM, volumetric and functional LV parameters demonstrated high correlations (LVESV: r=0.97, LVEDV: r=0.95, LVEF: r=0.91, LVMM: r=0.87, each p<0.05), but wide limits of agreement (LOA) for LVEDV (-25.3-82.5ml); LVESV (-33.1-72.7ml); LVEF (-18.9-14.8%) and LVMM (-78.2-43.2g). Intra- and interobserver reliability were very high (ICC≥0.95) for all parameters, except for MR-LVEF (ICC=0.87). PET-IQ (0-3) was high (mean: 2.2±0.9) with significant influence on LVMM calculations only. CONCLUSION: In simultaneously acquired cardiac PET/MRI data, LVEDV, LVESV and LVEF show good agreement. However, the agreement seems to be limited if cardiac PET/MRI follows PET/CT and only the residual activity is used. KEY POINTS: • [ 18 F] FDG PET-MRI is feasible with residual [ 18 F] FDG activity in patients with homogenous cardiac uptake. • Cardiac volumes and function assessed by PET/MRI show good agreement. • LVEDV and LVESV are underestimated; PET overestimates LVMM and LVEF. • Cardiac PET and MRI data correlate better when acquired simultaneously than sequentially. • PET and MRI should not assess LV parameters interchangeably.

[Epicardial ablation of ventricular tachycardias]. / Epikardiale Ablation ventrikulärer Tachykardien.

Ventricular tachycardias (VT) in patients with structural heart diseases have predominantly a scar-associated reentry mechanism so that substrate-based ablation approaches also have to be used in nearly all procedures. In many VT cases-especially in nonischemic cardiomyopathy (NICM) and arrhythmogenic right ventricular cardiomyopathy-a critical epicardial substrate can be identified as an essential component of the reentry circuit so that for the ablation-based modification of the substrate in these cases an epicardial approach is necessary. In cases of redo-VT ablation procedures in ischemic cardiomyopathy (after a previously endocardial ablation), an epicardial approach should also be considered. There are also cases in whom no endocardial substrate can be identified and an isolated epicardial substrate can be identified. Worldwide epicardial VT ablations are usually performed after gaining epicardial access using subxyphoidal puncture. The results of recent studies show a higher efficiency with stabilization of cardiac rhythm and reduction of recurrent VT episodes (about 70% event-free survival at the 2­year follow-up) after endo-plus epicardial substrate modification. In electrical storm cases, an early epicardial VT ablation approach also appears to be relevant, especially in NICM. Epicardial instrumentation and ablation represents a complex procedure which should only be performed in experienced centers with cardiac surgery back-up. In these experienced centers, the complications rate is less than 5%.

Relationship of plasma N-terminal pro-brain natriuretic peptide concentrations to heart failure classification and cause of respiratory distress in dogs using a 2nd generation ELISA assay.

BACKGROUND: Cardiac biomarkers provide objective data that augments clinical assessment of heart disease (HD). HYPOTHESIS/OBJECTIVES: Determine the utility of plasma N-terminal pro-brain natriuretic peptide concentration [NT-proBNP] measured by a 2nd generation canine ELISA assay to discriminate cardiac from noncardiac respiratory distress and evaluate HD severity. ANIMALS: Client-owned dogs (n = 291). METHODS: Multicenter, cross-sectional, prospective investigation. Medical history, physical examination, echocardiography, and thoracic radiography classified 113 asymptomatic dogs (group 1, n = 39 without HD; group 2, n = 74 with HD), and 178 with respiratory distress (group 3, n = 104 respiratory disease, either with or without concurrent HD; group 4, n = 74 with congestive heart failure [CHF]). HD severity was graded using International Small Animal Cardiac Health Council (ISACHC) and ACVIM Consensus (ACVIM-HD) schemes without knowledge of [NT-proBNP] results. Receiver-operating characteristic curve analysis assessed the capacity of [NT-proBNP] to discriminate between dogs with cardiac and noncardiac respiratory distress. Multivariate general linear models containing key clinical variables tested associations between [NT-proBNP] and HD severity. RESULTS: Plasma [NT-proBNP] (median; IQR) was higher in CHF dogs (5,110; 2,769-8,466 pmol/L) compared to those with noncardiac respiratory distress (1,287; 672-2,704 pmol/L; P < .0001). A cut-off >2,447 pmol/L discriminated CHF from noncardiac respiratory distress (81.1% sensitivity; 73.1% specificity; area under curve, 0.84). A multivariate model comprising left atrial to aortic ratio, heart rate, left ventricular diameter, end-systole, and ACVIM-HD scheme most accurately associated average plasma [NT-proBNP] with HD severity. CONCLUSIONS AND CLINICAL IMPORTANCE: Plasma [NT-proBNP] was useful for discriminating CHF from noncardiac respiratory distress. Average plasma [NT-BNP] increased significantly as a function of HD severity using the ACVIM-HD classification scheme.

Effective diameter of the aortic annulus prior to transcatheter aortic valve implantation: influence of area-based versus perimeter-based calculation.

In computed tomography (CT) evaluation prior to transcatheter aortic valve implantation area- and perimeter-based calculation of the aortic annulus diameter, the so-called effective annulus diameter (ED), is the preferred parameter for decision making regarding prosthesis sizes. Currently, it is unclear how relevant the differences between the two methods of measurement are and how they are influenced by the cardiac cycle. The aim of this study was to compare area- and perimeter-based measurements in computed tomography derived aortic annulus sizing. A total of 60 patients who underwent evaluation for transcatheter aortic valve implantation were included in this study. All patients received pre-procedural ECG gated CT. The aortic annulus area and perimeter were measured and the derived ED compared using parametric statistics and Bland and Altman analysis. The mean patient age was 80.2 ± 4 years. Systolic aortic annulus area and perimeter were higher compared to diastolic results (mean difference area 12.8 ± 24 mm(2) and perimeter 0.72 ± 1 mm; p = 0.009-0.068). Both the area- and perimeter-based ED had a good agreement within two standard deviations for systolic and diastolic measurements. Effective diameter measurements derived from the area were significantly smaller compared to perimeter-based measurements (mean difference: systolic 0.72 ± 0.3 mm and diastolic 0.81 ± 0.4 mm; p < 0.001). While the area-based ED was significantly influenced by the cardiac cycle with a mean difference of 0.4 ± 0.6 mm (p = 0.009), no significant difference was found for the perimeter-based ED (mean difference: 0.2 ± 0.4; p = 0.07). For patients undergoing CT evaluation prior to transcatheter aortic valve implantation, the perimeter-based effective annulus diameter provides a reliable parameter for annulus sizing without significant affection by the cardiac cycle and therefore facilitates annulus measurements with a single heart phase. However, perimeter-based diameters of the annulus are significantly larger than area-based diameters.

Post-processing in cardiovascular computed tomography: performance of a client server solution versus a stand-alone solution.

PURPOSE: To compare the performance of server-based (CSS) versus stand-alone post-processing software (ES) for the evaluation of cardiovascular CT examinations (cvCT) and to determine the crucial steps. MATERIALS AND METHODS: Data of 40 patients (20 patients for coronary artery evaluation and 20 patients prior to transcatheter aortic valve implantation [TAVI]) were evaluated by 5 radiologists with CSS and ES. Data acquisition was performed using a dual-source 128-row CT unit (SOMATOM Definition Flash, Siemens, Erlangen, Germany) and a 64-row CT unit (Brilliance 64, Philips, Hamburg, Germany). The following workflow was evaluated: Data loading, aorta and coronary segmentation, curved multiplanar reconstruction (cMPR) and 3 D volume rendering technique (3D-VRT), measuring of coronary artery stenosis and planimetry of the aortic annulus. The time requirement and subjective quality for the workflow were evaluated. RESULTS: The coronary arteries as well as the TAVI data could be evaluated significantly faster with CSS (5.5  ±  2.9  min and 8.2  ±  4.0  min, respectively) than with ES (13.9  ±  5.2  min and 15.2  ±â€Š 10.9  min, respectively, p ≤  0.01). Segmentation of the aorta (CSS: 1.9 ±  2.0  min, ES: 3.7  ±  3.3  min), generating cMPR of coronaries (CSS: 0.5  ±  0.2  min, ES: 5.1  ±  2.6  min), aorta and iliac vessels (CSS: 0.5  ±  0.4  min and 0.4  ±  0.4  min, respectively, ES: 1.6  ±  0.7  min and 2.8  ±  3  min, respectively) could be performed significantly faster with CSS than with ES with higher quality of cMPR, measuring of coronary stenosis and 3D-VRT (p < 0.05). CONCLUSION: Evaluation of cvCT can be accomplished significantly faster and better with CSS than with ES.  The segmentation remains the most time-consuming workflow step, so optimization of segmentation algorithms could improve performance even further.

[Imaging prior to transcatheter aortic valve implantation]. / Bildgebung vor Transkatheteraortenklappenersatz.

Percutaneous transcatheter aortic valve implantation (TAVI) is an established alternative to open heart surgery in patients with severe aortic stenosis (AS) unsuitable for conventional aortic valve replacement due to comorbidities with a high perioperative risk or contraindications. Preprocedural imaging plays a major role for adequate determination of indications and prosthesis selection, prosthesis sizing and therefore for a reduction of periprocedural complications. Besides Doppler echocardiography which is mainly used for grading of the severity of aortic valve stenosis and peri-interventional imaging, cardiac computed tomography (CCT) is the imaging modality of choice. The CCT procedure not only allows for reliably assessment and measuring of the complex 3-dimensional geometry of the aortic root but also for the aorta and the peripheral vessels used as potential access paths.

Role of preprocedural computed tomography in transcatheter aortic valve implantation.

UNLABELLED: Transcatheter aortic valve implantation (TAVI) is currently considered an acceptable alternative for the treatment of patients with severe aortic stenosis and a high perioperative risk or a contraindication for open surgery. The benefit of TAVI significantly outweighs the risk of the procedure in patients requiring treatment that are not suitable for open surgery, and leads to a lower mortality in the one-year follow-up. The absence of a direct view of the aortic root and valve remains a challenge for the transcatheter approach. While direct inspection of the aortic valve during open surgery allows an adequate prosthesis choice, it is crucial for TAVI to know the individual anatomical details prior to the procedure in order to assure adequate planning of the procedure and proper prosthesis choice and patient selection. Among the imaging modalities available for the evaluation of patients prior to TAVI, computed tomography (CT) plays a central role in patient selection. CT reliably visualizes the dimensions of the aortic root and allows a proper choice of the prosthesis size. The morphology of the access path and relevant comorbidities can be assessed. The present review summarizes the current state of knowledge regarding the value of CT in the evaluation of patients prior to TAVI. KEY POINTS: CT plays a central role in patient selection and planning prior to TAVI. ▶ CT reliably detects the dimensions of the aortic root including the size of the aortic annulus, the degree of valve calcification and the morphology of the access routes. ▶ CT provides a more accurate measurement of the aortic annulus than 2D TEE and CT is the only imaging modality that allows a risk assessment for paravalvular leakages based on the calcification of the aortic valve.

Experience with anatomically orientated devices for transapical aortic valve implantation.

Transcatheter aortic valve implantation (TAVI) is a new technology, which is rapidly growing to a routine procedure amenable for patients with symptomatic aortic valve stenosis and higher than average risk for conventional aortic valve surgery. The crucial disadvantage of TAVI remains the not well foreseeable risk of more than trivial degree of paravalvular leakage and a high rate of atrioventricular block and consecutive pacemaker implantation. In addition, current implantation techniques do not allow controlling the rotation of first-generation devices that might be beneficial regarding optimal physiological valve performance, optimal coronary flow and avoidance of placement of covered commissures in front of the coronary ostia. These shortcomings had pushed the development of second-generation self-expandable nitinol-based devices for subcoronary implantation that aim a reduction of paravalvular leak and AV-block by anatomical orientated positioning into the aortic root. This review focuses on the description of three different TAVI concepts, which are presently under early clinical evaluation, or have recently received commercial approval, using the transapical approach.

[MRI for myocarditis]. / MRT bei Myokarditis.

Cardiovascular magnetic resonance imaging (CMRI) has become the primary tool for the non-invasive assessment in patients with suspected myocarditis, especially after exclusion of acute coronary syndrome (ACS) for the differential diagnosis. Various MRI parameters are available which have different accuracies. Volumetric and functional ventricular assessment and the occurrence of pericardial effusion alone demonstrate only a poor sensitivity and specificity. The calculation of the T2-ratio (edema assessment), the early or global relative myocardial enhancement (gRE) and the late gadolinium enhancement (LGE), which represents irreversibly injured myocardium, are more specific parameters. All MRI parameters demonstrate the best accuracy in infarct-like acute myocarditis, whereas in chronic myocarditis sensitivity and specificity are less accurate. Therefore, a multisequential (at least two out of three parameters are positive) approach is recommended. The assessment of the value of newer, more quantitative MRI sequences, such as T1 and T2-mapping is still under investigation.

Role of preprocedural computed tomography in transcatheter aortic valve implantation.

UNLABELLED: Transcatheter aortic valve implantation (TAVI) is currently considered an acceptable alternative for the treatment of patients with severe aortic stenosis and a high perioperative risk or a contraindication for open surgery. The benefit of TAVI significantly outweighs the risk of the procedure in patients requiring treatment that are not suitable for open surgery, and leads to a lower mortality in the one-year follow-up. The absence of a direct view of the aortic root and valve remains a challenge for the transcatheter approach. While direct inspection of the aortic valve during open surgery allows an adequate prosthesis choice, it is crucial for TAVI to know the individual anatomical details prior to the procedure in order to assure adequate planning of the procedure and proper prosthesis choice and patient selection. Among the imaging modalities available for the evaluation of patients prior to TAVI, computed tomography (CT) plays a central role in patient selection. CT reliably visualizes the dimensions of the aortic root and allows a proper choice of the prosthesis size. The morphology of the access path and relevant comorbidities can be assessed. The present review summarizes the current state of knowledge regarding the value of CT in the evaluation of patients prior to TAVI. CT plays a central role in patient selection and planning prior to TAVI. CT reliably detects the dimensions of the aortic root including the size of the aortic annulus, the degree of valve calcification and the morphology of the access routes. KEY POINTS: CT plays a central role in patient selection and planning prior to TAVI. CT reliably detects the dimensions of the aortic root including the size of the aortic annulus, the degree of valve calcification and the morphology of the access routes. CT provides a more accurate measurement of the aortic annulus than 2D TEE and CT is the only imaging modality that allows a risk assessment for paravalvular leakages based on the calcification of the aortic valve.

Performance of an automatic dose control system for CT: patient studies.

PURPOSE: To study the effect of an automatic dose control (ADC) system with adequate noise characteristic on the individual perception of image noise and diagnostic acceptance compared to objectively measured image noise and the dose reductions achieved in a representative group of patients. MATERIALS AND METHODS: In a retrospective study two matched cohorts of 20 patients each were identified: a manual cohort with exposure settings according to body size (small - regular - large) and an ADC cohort with exposure settings calculated by the ADC system (DoseRight 2.0™, Philips Healthcare). For each patient, 12 images from 6 defined anatomic levels from contrast-enhanced scans of chest and abdomen/pelvis were analyzed by 4 independent readers concerning image noise and diagnostic acceptance on a five-point Likert scale and evaluated for objectively measured image noise. Radiation exposure was calculated from recorded exposure data. RESULTS: Use of the ADC system reduced the average effective dose for patients by 36 % in chest scans (3.2 vs. 4.9 mSv) and by 17 % in abdomen/pelvis scans (7.6 vs. 8.3 mSv). Average objective noise was slightly lower in the manual cohort (11.1 vs. 12.8 HU), correlating with a slightly better rating in subjective noise score (4.4 vs. 4.2). However, diagnostic acceptance was rated almost equal in both cohorts with excellent image quality (4.6 vs. 4.5). CONCLUSION: Use of an ADC system with adequate noise characteristic leads to significant reductions in radiation exposure for patients while maintaining excellent image quality.

Familial subvalvular aortic stenosis in golden retrievers: inheritance and echocardiographic findings.

OBJECTIVES: To describe the echocardiographic findings and pedigree analysis of golden retrievers with subvalvular aortic stenosis. METHODS: Seventy-three golden retrievers were evaluated by auscultation and echocardiography. A subcostal continuous-wave Doppler aortic velocity ê2·5 m/s and presence of a left basilar systolic ejection murmur were required for diagnosis of subvalvular aortic stenosis. Three echocardiographic characteristics were recorded: evidence of aortic insufficiency, subvalvular ridge or left ventricular hypertrophy. A disease status score was calculated by totalling the number of echocardiographic -characteristics per subject. RESULTS: Thirty-two of 73 dogs were affected and their aortic velocities were as follows: range 2·5 to 6·8 m/s, median 3·4 m/s and standard deviation 1·2 m/s. Echocardiographic characteristics of 32 affected dogs were distributed as follows: left ventricular hypertrophy 12 of 32, aortic insufficiency 20 of 32 and subvalvular ridge 20 of 32. Disease status score ranged from 0 to 3 with a median of 2. There was a statistically significant correlation between aortic velocity and disease status score (r=0·644, P<0·0001). Subvalvular aortic stenosis was observed in multiple generations of several families and appears familial. CLINICAL SIGNIFICANCE: Subvalvular aortic stenosis in the golden retriever is familial. Severity of stenosis correlates well with cumulative presence of echocardiographic characteristics (left ventricular hypertrophy, subvalvular ridge and aortic insufficiency).

Multicenter evaluation of plasma N-terminal probrain natriuretic peptide (NT-pro BNP) as a biochemical screening test for asymptomatic (occult) cardiomyopathy in cats.

BACKGROUND: B-type natriuretic peptide concentrations reliably distinguish between cardiac and respiratory causes of dyspnea, but its utility to detect asymptomatic cats with occult cardiomyopathy (OCM) is unresolved. HYPOTHESIS/OBJECTIVES: Determine whether plasma N terminal probrain natriuretic peptide (NT-proBNP) concentration can discriminate asymptomatic cats with OCM from normal cats, and whether NT-proBNP concentration correlates with clinical, biochemical, and echocardiographic parameters. ANIMALS: One hundred and fourteen normal, healthy cats; 113 OCM cats. METHODS: Prospective, multicenter, case-controlled study. NT-proBNP was prospectively measured and cardiac status was determined from history, physical examination, and M-mode/2D/Doppler echocardiography. Optimal cut-off values were derived using receiver operating characteristic (ROC) curve analysis. RESULTS: NT-proBNP was higher (median, interquartile range [25th and 75th percentiles]) in (1) OCM (186 pmol/L; 79, 478 pmol/L) versus normal (24 pmol/L; 24, 32 pmol/L) (P < .001); and (2) hypertrophic obstructive cardiomyopathy (396 pmol/L; 205, 685 pmol/L) versus hypertrophic cardiomyopathy (112 pmol/L; 48, 318 pmol/L) (P < .001). In OCM, NT-proBNP correlated (1) positively with LVPWd (ρ = 0.23; P = .01), LA/Ao ratio (ρ = 0.31; P < .001), LVs (ρ = 0.33; P < .001), and troponin-I (ρ = 0.64; P < .001), and (2) negatively with %FS (ρ = -0.27; P = .004). Area under ROC curve was 0.92; >46 pmol/L cut-off distinguished normal from OCM (91.2% specificity, 85.8% sensitivity); >99 pmol/L cut-off was 100% specific, 70.8% sensitive. CONCLUSIONS AND CLINICAL IMPORTANCE: Plasma NT-proBNP concentration reliably discriminated normal from OCM cats, and was associated with several echocardiographic markers of disease severity. Further studies are needed to assess test performance in unselected, general feline populations, and evaluate relationships between NT-proBNP concentrations and disease progression.

Time course of right ventricular functional parameters after surgical correction of tetralogy of Fallot determined by cardiac magnetic resonance.

AIM: To evaluate changes of right ventricular (RV) parameters in follow-up examinations after corrected tetralogy of Fallot (TOF) by cardiac magnetic resonance (CMR). METHODS: CMR was performed twice within 4 years in 45 patients using a 1.5 T scanner. RV-volumes and pulmonary-regurgitant-fractions (PRF) were calculated from standard cine-sequences and flow-sensitive gradient-echo images, respectively. Patients were divided into two groups depending on the post-operative (po) interval (group 1 ≤5 years po; group 2 >5 years po) and subgroups depending on type of surgery (transannular vs. non-transannular). Patient groups were compared among each other and differences between 1st and 2nd CMR were assessed. Furthermore, patients were compared with 25 healthy volunteers. RESULTS: Compared with controls RV-size was increased (group 1: p = 0.007; group 2: p < 0.001) and RV function decreased (group 1: p = 0.02; group 2: p < 0.001) in po TOF-patients. PRF was higher in group 2 compared with group 1 (p = 0.04) and significant changes of PRF between 1st and 2nd CMR were found in group 2 (p < 0.01), but not in group 1 (p = 0.29). Compared with the non-transannular subgroup, PRF (p < 0.001) and RV end-diastolic-volume index (RV-EDVI) (p = 0.03) were significantly higher in patients with a transannular patch, EDVI increased between 1st and 2nd CMR. After correction, no significant changes of RV myocardial mass index (RV-MMI) were found. CONCLUSION: After correction of TOF, RV-size, RV-muscle mass (RV-MM) was increased and ejection fraction decreased in "early" follow-up already. Whereas these parameters can remain stable over a long time period, the PRF significantly increased in "late" follow-up dependent on the po interval. Overall, transannular patching went along with higher PRF and bigger RV-size as well as a greater dynamic of these parameters in the time course, which makes this subgroup highly in need of regular follow-up examinations for the optimal timing of re-interventions. In contrast, the increased RV-MM demonstrated no regression po.

[Preoperative and postoperative imaging in patients with transposition of the great arteries]. / Prä- und Postoperative Bildgebung bei Patienten mit Transposition der großen Gefäße.

Transposition of the great arteries (TGA) is a rare disease representing not more than 3-5% of all congenital heart diseases. TGA is a cardiac anomaly in which the aorta arises entirely or largely from the morphological right ventricle and the pulmonary artery from the morphological left ventricle. This is called a ventriculo-arterial discordant connection and when accompanied by an atrio-ventricular concordant connection it is called a complete or D-transposition (D-TGA). The terms congenitally corrected TGA (ccTGA) or L-TGA describe an atrio-ventricular discordant connection. In D-TGA survival can only be achieved if additional shunting is simultaneously present, which possibly has to be created post-natal by the so-called Rashkind maneuver.Nowadays, an early anatomic correction using the arterial switch operation is the treatment of choice. Up to the 1980s, an atrial switch operation according to Senning/Mustard was performed. Apart from echocardiography the imaging modality of choice is usually MRI to assess the complex postoperative anatomy, viability of the myocardium and to perform a volumetric and functional assessment, including MR flow measurements. Multidetector computed tomography (MDCT) is used if there are contraindications to MRI or if an assessment of cardiac and especially coronary anatomy is the main interest.

Volume measurement of liver metastases using multidetector computed tomography: comparison of lesion diameter and volume segmentation - a phantom study.

PURPOSE: To compare lesion volume determination by applying diameter measurement and three different segmentation algorithms at different slice thicknesses reconstructed from computed tomography (CT) of a phantom model for hepatic colorectal metastases. MATERIALS AND METHODS: Based on CT attenuation measurements obtained retrospectively from 20 patients with colorectal liver metastases, a phantom model was designed with a sponge soaked with a dilution of contrast agent and 6 embedded polyamide spheres (diameter, 8 - 30 mm) to simulate the contrast behavior of liver metastases. CT scans were obtained and reconstructed at different slice thicknesses (0.625/1.25/2.5/3.75 mm; increment, 1). One observer performed software-aided volume determination using the maximum diameter, manual segmentation, seed point method, and threshold method six times for each lesion in a randomized order. Statistical analysis revealed the absolute and relative differences from the actual lesion volumes and the intraobserver differences as well as the influence of slice thickness for each method. RESULTS: The mean relative differences of the seed point method (1.2 - 5.9%) and manual segmentation (2.6 - 4.9%) were significantly lower than the threshold method (5.4 - 12.8%) and diameter measurement (12.3 - 18.5%; p < 0.01). Volume determination by manual segmentation and the seed point method benefited from the use of thin-slice CT datasets. The intraobserver variation was lowest when using the manual segmentation (1.5 - 3.3%) and the seed point method (2.2 - 3.9%; p < 0.001). CONCLUSION: Manual segmentation and the seed point method for thin CT slices were the methods with the lowest volume differences and intraobserver variation.