Delayed contrast‐enhanced MRI of cartilage (dGEMRIC) is a noninvasive technique to study cartilage glycosaminoglycan (GAG) content in vivo. This study evaluates dGEMRIC in patients with preradiographic degenerative cartilage changes. Seventeen knees in 15 patients (age 35–70) with arthroscopically verified cartilage changes (softening and fibrillations) in the medial or lateral femoral compartment, knee pain, and normal weight‐bearing radiography were included. MRI (1.5 T) was performed precontrast and at 1.5 and 3 hr after an intravenous injection of Gd‐DTPA²⁻at 0.3 mmol/kg body weight.T₁measurements were made in regions of interest in medial and lateral femoral cartilage using sets of five turbo inversion recovery images. Precontrast,R₁(R₁= 1/T₁, 1/s) was slightly lower in diseased compared to reference compartment, indicating increased hydration (P= 0.01). Postcontrast,R₁was higher in diseased than in reference compartment at 1.5 hr, 3.45 ± 0.90 and 2.64 ± 0.58 (mean ± SD), respectively (P< 0.01), as well as at 3 hr, 2.94 ± 0.60 and 2.50 ± 0.37, respectively (P= 0.01). The washout of the contrast medium was faster in diseased cartilage as shown by a higherR₁at 1.5 than at 3 hr in the diseased but not in the reference compartment. In conclusion, dGEMRIC can identify GAG loss in early stage cartilage disease with a higher sensitivity at 1.5 than 3 hr. Magn Reson Med 49:488–492, 2003.

MRI provides unsurpassed soft tissue contrast, but the inherent low sensitivity of this modality has limited the clinical use to imaging of water protons. With hyperpolarization techniques, the signal from a given number of nuclear spins can be raised more than 100 000 times. The strong signal enhancement enables imaging of nuclei other than protons, e.g. 13C and 15N, and their molecular distribution in vivo can be visualized in a clinically relevant time window. This article reviews different hyperpolarization techniques and some of the many application areas. As an example, experiments are presented where hyperpolarized 13C nuclei have been injected into rabbits, followed by rapid 13C MRI with high spatial resolution (scan time <1 s and 1.0 mm in-plane resolution). The high degree of polarization thus enabled mapping of the molecular distribution within various organs, a few seconds after injection. The hyperpolarized 13C MRI technique allows a selective identification of the molecules that give rise to the MR signal, offering direct molecular imaging.

Purpose: We describe a public dataset with MR and CT images of patients performed in the same position with both multiobserver and expert consensus delineations of relevant organs in the male pelvic region. The purpose was to provide means for training and validation of segmentation algorithms and methods to convert MR to CT like data, i.e., so called synthetic CT (sCT).Acquisition and validation methods: T1‐ and T2‐weighted MR images as well as CT data were collected for 19 patients at three different departments. Five experts delineated nine organs for each patient based on the T2‐weighted MR images. An automatic method was used to fuse the delineations. Starting from each fused delineation, a consensus delineation was agreed upon by the five experts for each organ and patient. Segmentation overlap between user delineations with respect to the consensus delineations was measured to describe the spread of the collected data. Finally, an open‐source software was used to create deformation vector fields describing the relation between MR and CT images to further increase the usability of the dataset.Data format and usage notes: The dataset has been made publically available to be used for academic purposes, and can be accessed from https://zenodo.org/record/583096.Potential applications: The dataset provides a useful source for training and validation of segmentation algorithms as well as methods to convert MR to CT‐like data (sCT). To give some examples: The T2‐weighted MR images with their consensus delineations can directly be used as a template in an existing atlas‐based segmentation engine; the expert delineations are useful to validate the performance of a segmentation algorithm as they provide a way to measure variability among users which can be compared with the result of an automatic segmentation; and the pairwise deformably registered MR and CT images can be a source for an atlas‐based sCT algorithm or for validation of sCT algorithm.

A ¹³C‐enriched water‐soluble compound (bis‐1,1‐(hydroxymethyl)‐1‐¹³C‐cyclopropane‐D₈), with a ¹³C‐concentration of approximately 200 mM, was hyperpolarized to ∼15% using dynamic nuclear polarization, and then used as a contrast medium (CM) for contrast‐enhanced magnetic resonance angiography (CE‐MRA). The long relaxation times (in vitro: T₁ ≈ 82 s, T₂ ≈ 18 s; in vivo: T₁ ≈ 38 s, T₂ ≈ 1.3 s) are ideal for steady‐state free precession (SSFP) imaging with a true fast imaging and steady precession (trueFISP) pulse sequence. It was shown both theoretically and experimentally that the optimal flip angle was 180°. CE‐MRA was performed in four anesthetized live rats after intravenous injection of 3 ml CM. The angiograms covered the thoracic/abdominal region in two of the animals, and the head‐neck region in the other two. Fifteen consecutive images were acquired in each experiment, with a flip‐back pulse at the end of each image acquisition. In the angiograms, the vena cava (SNR ≈ 240), aorta, renal arteries, carotid arteries (SNR ≈ 75), jugular veins, and several other vessels were visible. The SNR in the cardiac region was 500. Magnetization was preserved from one image acquisition to the next using the flip‐back technique (SNR_cardiac ≈ 10 in the 15th image). Magn Reson Med 50:256–262, 2003.

Objective: To examine the glycosaminoglycan (GAG) content in cartilage and that in synovial fluid and determine whether they are associated, in patients with an acute anterior cruciate ligament (ACL) injury.Methods: Twenty‐four patients (14 of whom were male) with a mean age of 27 years (range 17–40 years) were assessed with delayed gadolinium‐enhanced magnetic resonance imaging (MRI) of cartilage an average of 3 weeks after an ACL rupture and compared with 24 healthy volunteers. Two hours after an intravenous injection of Gd‐DTPA²⁻ (0.3 mmoles/kg body weight), quantitative measurements of the T1 relaxation time (T1_Gd [T1 relaxation time in the presence of Gd‐DTPA]) were made in lateral and medial femoral weight‐bearing cartilage. In the patients, synovial fluid was aspirated immediately before the MRI, and GAG was analyzed using dye precipitation with Alcian blue.Results: Fifteen of the 24 patients had an isolated bone bruise in the lateral femoral condyle, where the cartilage T1_Gd was shorter than that in the controls (mean ± SD 385 ± 83 msec and 445 ± 41 msec, respectively; P = 0.004), consistent with decreased GAG content. However, the T1_Gd was also decreased in the medial femoral cartilage, where bone bruises were rare (376 ± 76 msec in patients versus 428 ± 38 msec in controls; P = 0.006). The mean ± SD synovial fluid GAG concentration in patients was 157 ± 86 μg/ml and showed a positive correlation with the T1_Gd (r = 0.49, P = 0.02).Conclusion: This study indicates that an ACL injury causes posttraumatic edema of the lateral femoral cartilage but initializes a generalized biochemical change within the knee that leads to GAG loss from both lateral and medial femoral cartilage. In cartilage with a high GAG content (long T1_Gd), more GAG is released into the synovial fluid, suggesting that cartilage quality is a factor to consider when interpreting cartilage biomarkers of metabolism.