Noura Azzabou

Prior knowledge, random walks and human skeletal muscle segmentation

In this paper, we propose a novel approach for segmenting the skeletal muscles in MRI automatically. In order to deal with the absence of contrast between the different muscle classes, we proposed a principled mathematical formulation that integrates prior knowledge with a random walks graph-based formulation. Prior knowledge is represented using a statistical shape atlas that once coupled with the random walks segmentation leads to an efficient iterative linear optimization system. We reveal the potential of our approach on a challenging set of real clinical data.

Validation of a generic approach to muscle water T2 determination at 3T in fat-infiltrated skeletal muscle

To introduce a novel method for skeletal muscle water T2 determination in fat‐infiltrated tissues, using a tri‐exponential fit of the global muscle signal decay.

Quantitative NMRI and NMRS identify augmented disease progression after loss of ambulation in forearms of boys with Duchenne muscular dystrophy.

Quantitative NMRI and 31P NMRS indices are reported in the forearms of 24 patients with Duchenne muscular dystrophy (DMD) (6–18 years, 14 non‐ambulant) amenable to exon 53 skipping therapy and in 12 age‐matched male controls (CONT). Examinations carried out at 3 T comprised multi‐slice 17‐echo measurements of muscle water T2 and heterogeneity, three‐point Dixon imaging of fat fraction in flexor and extensor muscles (FLEX, EXT), and non‐localised spectroscopy of phosphate metabolites. We studied four imaging indices, eight metabolic ratios combining ATP, phosphocreatine, phosphomonoesters and phosphodiesters, the cytosolic inorganic phosphate (Pia) and an alkaline (Pib) pool present in dystrophic muscle, and average pH. All indices differed between DMD and CONT, except for muscle water T2. Measurements were outside the 95th percentile of age‐matched CONT values in over 65% of cases for percentage fat signal (%F), and in 78–100% of cases for all spectroscopic indices. T2 was elevated in one‐third of FLEX measurements, whereas %pixels > 39 ms and T2 heterogeneity were abnormal in one‐half of the examinations. The FLEX muscles had higher fat infiltration and T2 than EXT muscle groups. All indices, except pH, correlated with patient age, although the correlation was negative for T2. However, in non‐ambulant patients, the correlation with years since loss of ambulation was stronger than the correlation with age, and the slope of evolution per year was steeper after loss of ambulation. All indices except Pi/gATP differed between ambulant and non‐ambulant patients; however, T2 and %pixels > 39 ms were highest in ambulant patients, possibly owing to the greater extent of inflammatory processes earlier in the disease. All other indices were worse in non‐ambulant subjects. Quantitative measurements obtained from patients at different disease stages covered a broad range of abnormalities that evolved with the disease, and metabolic indices were up to 10‐fold above normal from the onset, thus establishing a variety of potential markers for future therapy. Copyright

Manual segmentation of individual muscles of the quadriceps femoris using MRI: A reappraisal

To propose a manual segmentation method for individual quadriceps femoris (QF) muscles and to test its reliability for muscle volume estimation.

Comprehensive longitudinal characterization of canine muscular dystrophy by serial NMR imaging of GRMD dogs

The Golden Retriever Muscular Dystrophy (GRMD) dog is the closest animal counterpart of Duchenne muscular dystrophy in humans and has, for this reason, increasingly been used in preclinical therapeutic trials for this disease. The aim of this study was to describe the abnormalities in canine dystrophic muscle non-invasively, quantitatively, thoroughly and serially by means of NMR imaging. Thoracic and pelvic limbs of five healthy and five GRMD dogs were imaged in a 3T NMR scanner at 2, 4, 6 and 9months of age. Standard and fat-saturated T(1)-, T(2)- and proton-density-weighted images were acquired. A measurement of T(1) and a two-hour kinetic study of muscle enhancement after gadolinium-chelate injection were also performed. Ten out of the 15 indices evaluated differed between healthy and GRMD dogs. The maximal relative enhancement after gadolinium injection and the proton-density-weighted/T(2)-weighted signal ratio were the most discriminating indices. Inter-muscle heterogeneity was found to vary significantly for most of the indices. The body of data that has been acquired here will help in designing and interpreting preclinical trials using dystrophin-deficient dogs.

3D freehand ultrasound reconstruction based on probe trajectory

3D freehand ultrasound imaging is a very attractive technique in medical examinations and intra-operative stage for its cost and field of view capacities. This technique produces a set of non parallel B-scans which are irregularly distributed in the space. Reconstruction amounts to computing a regular lattice volume and is needed to apply conventional computer vision algorithms like registration. In this paper, a new 3D reconstruction method is presented, taking explicitly into account the probe trajectory. Experiments were conducted on different data sets with various probe motion types and indicate that this technique outperforms classical methods, especially on low acquisition frame rate.

Automatic skeletal muscle segmentation through random walks and graph-based seed placement

In this paper we propose a novel skeletal muscle segmentation method driven from discrete optimization. We introduce a graphical model that is able to automatically determine appropriate seed positions with respect to the different muscle classes. This is achieved by taking into account the expected local visual and geometric properties of the seeds through a pair-wise Markov Random Field. The outcome of this optimization process is fed to a powerful graph-based diffusion segmentation method (random walker) that is able to produce very promising results through a fully automated approach. Validation on challenging data sets demonstrates the potentials of our method.

Longitudinal functional and NMR assessment of upper limbs in Duchenne muscular dystrophy.

Objective: To explore the value of nuclear magnetic resonance (NMR) and functional assessments for follow-up of ambulatory and nonambulatory patients with Duchenne muscular dystrophy (DMD). Methods: Twenty-five 53-skippable patients with DMD were included in this study; 15 were nonambulatory at baseline. All patients underwent clinical and functional assessments every 6 months using the Motor Function Measure (MFM), hand grip and key pinch strength, MoviPlate, and NMR spectroscopy and imaging studies. Results: Upper limb distal strength decreased in nonambulatory patients over the period of 1 year; ambulatory patients showed improvement during the same period. The same applied for several NMRS indices, such as phosphocreatine/adenosine triphosphate, which decreased in older patients but increased in younger ambulatory patients. Fat infiltration in the upper limbs increased linearly with age. Almost all NMR and functional assessment results correlated. Conclusions: Our results underscore complementarity of functional and NMR assessments in patients with DMD. Sensitivity to change of various indices may differ according to disease stage.

NMR based biomarkers to study age-related changes in the human quadriceps

Age-related sarcopenia is a major health issue. To improve elderly person quality of life, it is important to characterize age-associated structural changes within the skeletal muscle. NMR imaging offers quantitative tools to monitor these changes. We scanned 93 subjects: 33 young adults aged between 19 and 27 years old and 60 older adults between 69 and 80 years old. Their physical activity was assessed using a tri-axial accelerometer and they were classified either as active or sedentary. A standard multi-slice multi-echo (MSME) sequence was run and water T2 maps were extracted using a tri-exponential fit. Fat fraction was quantified using three-point Dixon technique. Each quadriceps muscle was characterized by: water T2 mean value, water T2 heterogeneity and the mean fat fraction. Statistical analysis (ANOVA) showed that water T2 mean values and its heterogeneity indices as well as fat fraction were significantly higher in the elderly group (p<0.05). Only fat fraction was significantly lower in the active group compared to the sedentary one (p<0.05). Linear regression confirmed the significant impact of age on these NMR parameters whereas physical activity impact was not systematic. NMR imaging provided a comprehensive assessment of the aging process impact on skeletal muscle composition. Water T2 increase might be related to changes in fiber typology while increased T2 heterogeneities might correlate with some degree of tissue disorganization, like the development of interstitial fibrosis. Fat fraction and water T2 heterogeneity increase was partly slowed down by physical activity. These changes were not gender dependent.

Simultaneous muscle water T2 and fat fraction mapping using transverse relaxometry with stimulated echo compensation

Skeletal muscle inflammation/necrosis and fat infiltration are strong indicators of disease activity and progression in many neuromuscular disorders. They can be assessed by muscle T2 relaxometry and water‐fat separation techniques, respectively. In the present work, we exploited differences between water and fat T1 and T2 relaxivities by applying a bi‐component extended phase graph (EPG) fitting approach to simultaneously quantify the muscle water T2 and fat fraction from standard multi‐slice multi‐echo (MSME) acquisitions in the presence of stimulated echoes. Experimental decay curves were adjusted to the theoretical model using either an iterative non‐negative least‐squares (NNLS) procedure or a pattern recognition approach. Twenty‐two patients (age, 49 ± 18 years) were selected to cover a large range of muscle fat infiltration. Four cases of chronic or subchronic juvenile dermatomyositis (age, 8 ± 3 years) were investigated before and 3 months following steroid treatment. For control, five healthy volunteers (age, 25 ± 2 years) were recruited. All subjects underwent the MSME sequence and EPG fitting procedure. The EPG fitting algorithm allowed a precise estimation of water T2 and fat fraction in diseased muscle, even in the presence of large B1+ inhomogeneities. In the whole cohort of patients, there was no overall correlation between water T2 values obtained with the proposed method and the fat fraction estimated inside muscle tissues (R2 = 0.02). In the patients with dermatomyositis, there was a significant decrease in water T2 (‐4.09 ± 3.7 ms) consequent to steroid treatment. The pattern recognition approach resulted in a 20‐fold decrease in processing time relative to the iterative NNLS procedure. The fat fraction derived from the EPG fitting approach correlated well with the fat fraction derived from a standard three‐point Dixon method (≈1.5% bias). The bi‐component EPG fitting analysis is a precise tool to monitor muscle tissue disease activity and is able to handle bias introduced by fat infiltration and B1+ inhomogeneities. Copyright