[Defect models for the regeneration of articular cartilage in large animals]. / Defektmodelle für die Gelenkknorpelregeneration im Großtier.

BACKGROUND: Several animal models are available for the analysis of regeneration of articular cartilage in large animals, such as sheep, pigs, goats, dogs and horses. The subchondral bone lamella must be considered when ACT and MACT techniques are examined in order to protect the implant against migration of cells from the bone marrow, although recruitment of cells is often desirable in the regeneration of human cartilage. MATERIAL AND METHODS: The defects are mainly positioned at the condyles and the trochlea often bilaterally and spontaneous healing should be excluded. The follow-up period for assessment of the effectiveness of cartilage regeneration is 6-12 months. Shorter observation times up to 12 weeks can be used for pilot studies. Scores based on histological, immunohistological and biochemical staining are mostly used for assessing the regenerated tissue. Biomechanical tests with destructive features need isolated specimens from the animal but modern slice imaging techniques can reflect the progression of the healing processes over the time span of the study in vivo. CONCLUSION: Approaches to standardize the evaluation of the regeneration of articular cartilage have been sporadically described whereas they are required from the point of view of the approval of new concepts for therapy and the protection of animals.

Impact of iterative reconstruction on CNR and SNR in dynamic myocardial perfusion imaging in an animal model.

OBJECTIVES: To evaluate a new iterative reconstruction (IR) algorithm for radiation dose, image quality (IQ), signal-to-noise-ratio (SNR), and contrast-to-noise-ratio (CNR) in multidetector computed tomography (MDCT) dynamic myocardial perfusion imaging (MPI). METHODS: ECG-gated 256-slice MDCT dynamic MPI was performed in six pigs after subtotal balloon occlusion of one artery. Two 100 kVp protocols were compared: high dose (HD): 150 mAs; low dose (LD): 100 mAs. HD images were reconstructed with filtered back projection (FBP), LD images with FBP and different strengths of IR (L1, L4, and L7). IQ (5-point scale), SNR, and CNR (ischemic vs. normal myocardium) values derived from the HD (FBP) images and the different LD images were compared. RESULTS: Mean SNR values for myocardium were 16.3, 11.3, 13.1, 17.1, and 28.9 for the HD, LD (FBP), LD (L1), LD (L4), and LD (L7) reconstructions, respectively. Mean CNR values were 8.9, 6.3, 7.8, 9.3, and 12.8. IQ was scored as 4.6, 3.3, 4.4, 4.7, and 3.4, respectively. A significant loss of IQ was observed for the LD (L7) images compared to the HD (FBP) images (P < 0.05). CONCLUSION: Appropriate levels of iterative reconstruction can improve SNR and CNR, facilitating radiation dose savings in CT-MPI without influencing diagnostic quality. KEY POINTS: Iterative reconstruction (IR) can reduce radiation dose in myocardial perfusion CT. Our study also demonstrated improvements in image quality (noise, SNR, and CNR). Dynamic CT-MPI could help determine the hemodynamic significance of coronary artery disease. With dynamic CT MPI, myocardial blood flow can be determined quantitatively.