H. von Tengg-Kobligk

3D printing based on imaging data: review of medical applications

PurposeGeneration of graspable three-dimensional objects applied for surgical planning, prosthetics and related applications using 3D printing or rapid prototyping is summarized and evaluated.Materials and methodsGraspable 3D objects overcome the limitations of 3D visualizations which can only be displayed on flat screens. 3D objects can be produced based on CT or MRI volumetric medical images. Using dedicated post-processing algorithms, a spatial model can be extracted from image data sets and exported to machine-readable data. That spatial model data is utilized by special printers for generating the final rapid prototype model.ResultsPatient–clinician interaction, surgical training, medical research and education may require graspable 3D objects. The limitations of rapid prototyping include cost and complexity, as well as the need for specialized equipment and consumables such as photoresist resins.ConclusionsMedical application of rapid prototyping is feasible for specialized surgical planning and prosthetics applications and has significant potential for development of new medical applications.

Contrast agents for MRA: Future directions

The purpose of this review is to outline recent developments in contrast agents for magnetic resonance angiography (MRA) and to give some idea of what the future might hold. Up to now, non‐binding gadolinium (Gd) chelates have been the agents used for MRA. Modified paramagnetic Gd‐based agents with varying degrees of protein interaction have been developed, and these, together with new superparamagnetic compounds, are currently under clinical evaluation. It is likely that two different types of contrast agent will soon be available: extracellular agents for first‐pass MRA and intravascular agents mainly for steady‐state MRA. Several agents also exhibit certain tissue specific properties in addition to conventional extracellular properties. This will lead to more comprehensive imaging approaches.J. Magn. Reson. Imaging 10:314–316, 1999.

Semi-automated volumetric analysis of lymph node metastases in patients with malignant melanoma stage III/IV-A feasibility study

Therapy monitoring in oncological patient care requires accurate and reliable imaging and post-processing methods. RECIST criteria are the current standard, with inherent disadvantages. The aim of this study was to investigate the feasibility of semi-automated volumetric analysis of lymph node metastases in patients with malignant melanoma compared to manual volumetric analysis and RECIST. Multislice CT was performed in 47 patients, covering the chest, abdomen and pelvis. In total, 227 suspicious, enlarged lymph nodes were evaluated retrospectively by two radiologists regarding diameters (RECIST), manually measured volume by placement of ROIs and semi-automated volumetric analysis. Volume (ml), quality of segmentation (++/−−) and time effort (s) were evaluated in the study. The semi-automated volumetric analysis software tool was rated acceptable to excellent in 81% of all cases (reader 1) and 79% (reader 2). Median time for the entire segmentation process and necessary corrections was shorter with the semi-automated software than by manual segmentation. Bland-Altman plots showed a significantly lower interobserver variability for semi-automated volumetric than for RECIST measurements. The study demonstrated feasibility of volumetric analysis of lymph node metastases. The software allows a fast and robust segmentation in up to 80% of all cases. Ease of use and time needed are acceptable for application in the clinical routine. Variability and interuser bias were reduced to about one third of the values found for RECIST measurements.

Assessment of gadobenate dimeglumine for magnetic resonance angiography: Phase I studies

Knopp MV, Schoenberg SO, Rehm C, et al. Assessment of Gadobenate Dimeglumine for magnetic resonance angiography: Phase I studies. Invest Radiol 2002;37:706–715. Rationale and Objectives. To assess the vascular contrasting properties of a new MR contrast agent (gadobenate dimeglumine [Gd-BOPTA]), which presents higher relaxivity because of reversible, weak protein interaction, and, to compare these properties with a standard gadolinium agent. Materials and Methods. Two phase I trials compared intraindividually: (A) the vascular contrasting properties of Gd-BOPTA at three doses (0.0125, 0.05, and 0.2 mmol/kg body weight) and two flow rates (0.5 and 2.0 mL/s) in 10 volunteers; and (B) 0.1 mmol/kg body weight doses of Gd-BOPTA and Gd-DTPA at 2.0 mL/s using a modified magnetic resonance angiography (MRA) sequence with a temporal resolution of 1 s/f. Quantitative (ROI analysis) and fully blinded qualitative (reader review) assessment of images was performed. Results. A dose of 0.2 mmol/kg resulted in higher maximum intensities, longer median peak widths, and larger areas under the curve than did the lower doses (0.0125 mmol/kg and 0.05 mmol/kg). In the intraindividual comparison, Gd-BOPTA demonstrated significantly better vascular enhancement characteristics in terms of signal peak duration (p < 0.05), maximum signal intensity (p < 0.05), and area under the enhancement curve (p < 0.01). The multireader assessment for overall vascular contrast preferred Gd-BOPTA at p < 0.03. Conclusions. Gd-BOPTA was shown to exhibit preferential and different vascular enhancement properties as compared with Gd-DTPA for MRA.

A New Invasion Score for Determining the Resectability of Pancreatic Carcinomas with Contrast-Enhanced Multidetector Computed Tomography

Objective: It was the aim of this study to evaluate a new infiltration score to determine the resectability of pancreatic carcinomas in preoperative planning. Materials and Methods: Eighty patients with suspected pancreatic tumor were examined prospectively using 16-row spiral CT. The scans were evaluated for the presence of pancreatic carcinoma, peripancreatic tumor extension and vascular invasion using a standardized questionnaire. Invasion of the surgically relevant vessels was evaluated using a new invasion score. The operative and histological findings and the clinical follow-up served as the gold standard. Results: Forty patients had a pancreatic carcinoma, 5 had metastasis of a different primary tumor, and in 35 patients, there was no malignant pancreatic disease. The sensitivity for tumor detection was 100%, with a specificity of 88% for differentiating between malignant and benign pancreatic tumors. Invasion of the surrounding vessels was evaluated correctly using the invasion score, with a sensitivity of 89% and a specificity of 99%. In evaluation of resectability, a sensitivity of 94% and a specificity of 89% were achieved. Conclusion: Using 16-row spiral CT, the invasion score is a valid tool for correctly assessing invasion in relevant vessels in cases of pancreatic carcinoma and for determining resectability.

Intraindividueller Vergleich dreier Kontrastmittel (Gd-DTPA, Gd-BOPTA und Gd-BT-DO3A) mit der multiphasischen MR-Angiographie

ZusammenfassungFragestellung. Mit der Verfügbarkeit neuartiger Kontrastmittel – proteininteragierend oder höher konzentriert – stellt sich die Frage, ob und wie sich diese von den Standardkontrastmitteln hinsichtlich der vaskulären Kontrastierung unterscheiden. Methodik. In einer intraindividuellen Vergleichsstudie des Abdomens (1,5 T-MRTSystem) wurden 5 Probanden mit einer multiphasischen MRA jeweils mit 3 verschiedenen MR-Kontrastmitteln (Gadopentetat-Dimeglumin 0,5 M;Gadobenat-Dimeglumin 0,5 M und Gadobutrol 1,0 M) untersucht. Dosis (0,15 mmol/kg Körpergewicht) und Flussrate (3,0 ml/s) waren für alle 3 Kontrastmittel identisch. Die Untersuchungen wurden geblindet qualitativ und quantitativ evaluiert. Ergebnisse. Das proteininteragierende Gadobenat-Dimeglumin erzielte im Vergleich mit den anderen Kontrastmitteln signifikant höhere Signalintensitäten in den arteriellen Gefäßen (p = 0,05). Es wurde aufgezeigt, dass zwischen Gadopentetat-Dimeglumin und Gadobutrol 1,0 M keine signifikante Differenz in der vaskulären Kontrastierungseigenschaften besteht. Schlussfolgerung. Gadobenat-Dimeglumin hat sich als vorteilhaftes Kontrastmittel für die multiphasische MRA herausgestellt. Höher konzentrierte Gd-Chelate führen unter standardisierter Bildgebung nicht automatisch zu verbesserten Kontrastierungseffekten.AbstractQuestion. The availability of new MR contrast agents having either a protein binding effect or higher concentration leads to the question if they differ from standard compounds in their vascular contrasting properties. Methods. By intraindividual comparison five volunteers were examined (1.5 T MR system) with a multi-phasic MRA of the abdomen each receiving three different contrast agents (gadopentetate dimeglumine 0.5 M; gadobenate dimeglumine 0.5 M, and gadobutrol 1.0 M).The dose (0.15 mmol/kg body weight) and flow rate (3.0 ml/s) were kept identical. All images were quantitatively and qualitatively evaluated by blinded assessment. Results. Significantly higher maximum signal intensity was found in the arteries for the protein interacting gadobenate dimeglumine (p = 0.05). No significant difference in vascular enhancement was demonstrated in the comparison of gadobutrol to gadopentetate dimeglumine. Conclusion. Gadobenate dimeglumine was shown to be a favorable contrast agent for multi-phasic MRA. A higher concentrated Gd-chelate does not automatically lead to improved vascular contrast if standard imaging protocols are used.

Accuracy and Variability of Semiautomatic Centerline Analysis versus Manual Aortic Measurement Techniques for TEVAR

OBJECTIVES This study aims to test whether inter-observer variability and time of diameter measurements for thoracic endovascular aortic repair (TEVAR) are improved by semiautomatic centerline analysis compared to manual assessment. METHODS Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 males) were retrospectively analysed by two blinded experts in vascular radiology. Maximum aortic diameters at three positions relevant to TEVAR were assessed (P1, distal to left common carotid artery; P2, distal to left subclavian artery; and P3, proximal to coeliac trunk) using three measurement techniques: manual axial slices (axial), manual double-oblique multiplanar reformations (MPRs) and semiautomatic centerline analysis. RESULTS Diameter measurements by both centerline analysis and the axial technique did not significantly differ from MPR (p = 0.17 and p = 0.37). Total deviation index for 0.9 was for P1 2.7 mm (axial), 3.7 mm (MPR), 1.8 mm (centerline); for P2 2.0 mm (axial), 3.6 mm (MPR), 1.8 mm (centerline); and for P3 3.0 mm (axial), 3.5 mm (MPR), 2.5 mm (centerline). Measurement time using centerline analysis was significantly shorter than for assessment by MPR. CONCLUSIONS Centerline analysis provides the least variable and fast diameter measurements in TEVAR patients with the same accuracy as the current reference standard MPR.

Reliability of Semiautomatic Centerline Analysis versus Manual Aortic Measurement Techniques for TEVAR among Non-experts

OBJECTIVES The study aimed to test whether reliability and inter-observer variability of preoperative measurements for thoracic endovascular aortic repair (TEVAR) among non-experts are improved by semiautomatic centerline analysis compared with manual assessment. METHODS Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 men) were retrospectively analysed in randomised order by one blinded vascular expert (reference standard) and three blinded non-expert readers. Aortic diameters were measured at four positions relevant to TEVAR using three measurement techniques (manual axial slices, manual multiplanar reformations (MPRs) and semiautomatic centerline analysis). Length measurements were performed using centerline analysis. Reliability was calculated as absolute measurement deviation (AMD) from reference standard and inter-observer variability as coefficient of variance (CV) among non-expert readers. RESULTS For axial, MPR and centerline techniques, mean AMD was 7.3 ± 7.7%, 6.7 ± 4.5% and 4.7 ± 4.8% and mean CV was 5.2 ± 4.2%, 5.8 ± 4.8% and 3.9 ± 5.4%. Both AMD and CV were significantly lower for centerline analysis compared with axial technique (p = 0.001/0.042) and MPR (p = 0.009/0.003). AMD and CV for length measurements by centerline analysis were 3.2 ± 2.8% and 2.6 ± 2.4%, respectively. Centerline analysis was significantly faster than MPR (p < 0.001). CONCLUSIONS Semiautomatic centerline analysis provides the most reliable and least variable diameter and length measurements among non-experts in candidates for TEVAR.

Aktuelle Bildnachverarbeitung der aortalen CTA und MRA

ZusammenfassungDie multiplanare Reformatierung (MPR) der Bilddaten aortaler CTA und MRA ist die wichtigste Rekonstruktionsmethode im Hinblick auf eine differenzierte Therapieentscheidung und die präoperative Therapieplanung sowie die Beschreibung postoperativer Komplikationen. Die gekrümmte MPR wird semiautomatisch bzw. vollständig automatisch als Centerline im Gefäßlumen berechnet und für die Bestimmung des orthogonalen Durchmessers und der Längsausdehnung der Pathologie verwendet. Eine reproduzierbar exakte Ausmessung komplexer Pathologien und Gefäßlängsverläufe erweitert das Spektrum der diagnostischen Radiologie. Die gekrümmte MPR dient der semiautomatischen Berechnung der Gefäßmittellinie. Die heutigen Gerätekonsolen können bereits automatisch Maximum-Intensitätsprojektionen (MIP) und Standard-MPR anfertigen und ins Archiv versenden. Die 3D-Visualisierung kann als Volume-rendering-Technik (VRT) effektiv bei der Patientenselektion, Therapieplanung und Nachsorge behilflich sein und in der interdisziplinären Kommunikation des klinischen Alltags ergänzend zu den Quelldaten eingesetzt werden. Die Segmentierung von Hochkontraststrukturen ist meist semiautomatisch möglich, Weichteilstrukturen müssen jedoch weiterhin manuell segmentiert werden. Zur Bildnachverarbeitung sind isotrope CTA-Daten meist besser geeignet als MR-Datensätze, die häufig noch anisotrop sind. In vielen europäischen Ländern wird die Bildnachverarbeitung noch nicht adäquat vergütet, obwohl die Überweiser die 3D-Visualisierungen und Vermessungen oftmals mit Nachdruck einfordern.AbstractMultiplanar reformation (MPR) is the most relevant tool for patient selection and precise procedural planning and also for analyzing postinterventional complications. Curved MPR is used primarily for semiautomated or completely automated calculation of the centerline of the vascular lumen and to estimate the orthogonal vessel diameter and longitudinal extent. Reproducible and accurate measurement of complex pathologies and courses of vessels extends the range of diagnostic radiology. Contemporary scanner consoles allow automated processing of maximum intensity projections (MIP) and standard MPR and their storage in PACS. To improve patient selection, procedural planning, root-cause analysis postoperatively for assessment of treatment effects and to make better communication of findings to nonradiologists possible, volume rendering techniques (VRT) are a beneficial adjunct to source images. With current algorithms semiautomated segmentation is satisfactory for vessels and bones, but not for low-contrast structures (soft tissues), which still need to be segmented manually. In general, isotropic CT source data are preferable to MR images, which are often anisotropic. In many European countries image postprocessing is still not adequately reimbursed although the doctors making referrals often specifically and emphatically demand 3D visualization and measurements in daily practice.Multiplanar reformation (MPR) is the most relevant tool for patient selection and precise procedural planning and also for analyzing postinterventional complications. Curved MPR is used primarily for semiautomated or completely automated calculation of the centerline of the vascular lumen and to estimate the orthogonal vessel diameter and longitudinal extent. Reproducible and accurate measurement of complex pathologies and courses of vessels extends the range of diagnostic radiology. Contemporary scanner consoles allow automated processing of maximum intensity projections (MIP) and standard MPR and their storage in PACS. To improve patient selection, procedural planning, root-cause analysis postoperatively for assessment of treatment effects and to make better communication of findings to nonradiologists possible, volume rendering techniques (VRT) are a beneficial adjunct to source images. With current algorithms semiautomated segmentation is satisfactory for vessels and bones, but not for low-contrast structures (soft tissues), which still need to be segmented manually. In general, isotropic CT source data are preferable to MR images, which are often anisotropic. In many European countries image postprocessing is still not adequately reimbursed although the doctors making referrals often specifically and emphatically demand 3D visualization and measurements in daily practice.

Benign prostate hyperplasia: evaluation of treatment response with DCE MRI.

Benign prostate hyperplasia (BPH) is a major disease and its non-surgical therapy a major area of interest. The purpose of this study was to establish perfusion parameters in beagles with BPH using dynamic contrast-enhanced (DCE) MRI and to investigate changes due to the effects of finasteride treatment. Twelve male beagles (mean age 4.4±0.9,years) were divided into a control and treatment group that received a daily dose of 1 mg/kg finasteride. DCE MRI was carried out in a clinical scanner using a 3D spoiled gradient echo sequence prior to and during treatment. 0.2 mmol/kg contrast agent (gadoteridol) was administered with an injection rate of 0.2 ml/s followed by a 15 ml flush of saline. Contrast enhancement was evaluated by pharmacokinetic mapping of a two-compartment model with colour overlay images in addition to regional ROI analysis. Quantitative parameters were defined by the amplitude of contrast enhancement A, the exchange rate kep and the time to maximum signal enhancement. Dynamic contrast-enhanced MRI investigations of the prostate revealed two distinct zones, an inner, periurethral zone and an outer, parenchymal zone. The periurethral zone is highly vascularized, whereas the parenchymal zone is moderately vascularized when compared to other parenchymal organs. During treatment, in the parenchymal zone the intensity of enhancement (amplitude A) and the time to maximum signal enhancement increased, while the exchange rate kep decreased. Dynamic contrast-enhanced MRI of BPH reveals distinct differences between individual zones within the prostate. Moreover, changes during successful treatment suggest increased blood volume per volume of tissue and decreased vessel leakiness.