The intent of this paper is to discuss the evolving role of the myofascial trigger point (MTrP) in myofascial pain syndrome (MPS) from both a historical and scientific perspective. MTrPs are hard, discrete, palpable nodules in a taut band of skeletal muscle that may be spontaneously painful (i.e. active), or painful only on compression (i.e. latent). MPS is a term used to describe a pain condition which can be acute or, more commonly, chronic and involves the muscle and its surrounding connective tissue (e.g. fascia). According to Travell and Simons, MTrPs are central to the syndrome—but are they necessary? Although the clinical study of muscle pain and MTrPs has proliferated over the past two centuries, the scientific literature often seems disjointed and confusing. Unfortunately, much of the terminology, theories, concepts, and diagnostic criteria are inconsistent, incomplete, or controversial. In order to address these deficiencies, investigators have recently applied clinical, imaging (of skeletal muscle and brain), and biochemical analyses to systematically and objectively study the MTrP and its role in MPS. Data suggest that the soft tissue milieu around the MTrP, neurogenic inflammation, sensitization, and limbic system dysfunction may all play a role in the initiation, amplification, and perpetuation of MPS. The authors will chronicle the advances that have led to the current understanding of MTrP pathophysiology and its relationship to MPS, and review the contributions of clinicians and researchers who have influenced and expanded our contemporary level of clinical knowledge and practice.

Objective-Apply ultrasound (US) imaging techniques to better describe the characteristics of myofascial trigger points (MTrPs) and the immediately adjacent soft tissue.Design-Descriptive (exploratory) study. Setting-Biomedical research center.Participants-9 subjects meeting Travell and Simons's criteria for MTrPs in a taut band in the upper trapezius. Interventions-(None)Main Outcome Measures-MTrPs were evaluated by 1) physical examination, 2) pressure algometry, and 3) three types of ultrasound imaging including grayscale (2D US), vibration sonoelastography (VSE), and Doppler.Methods-Four sites in each patient were labeled based on physical examination as either active MTrP (spontaneously-painful, A-MTrP), latent MTrP (non-painful, L-MTrP), or normal myofascial tissue. US examination was performed on each subject by a team blinded to the physical findings. A 12-5 MHz US transducer was used. VSE was performed by color Doppler variance imaging while simultaneously inducing vibrations (~92Hz) with a handheld massage vibrator. Each site was assigned a tissue imaging score (TIS) as follows: 0 = uniform echogenicity and stiffness; 1 = focal hypoechoic region with stiff nodule; 2 = multiple hypoechoic regions with stiff nodules. Blood flow in the neighborhood of MTrPs was assessed using Doppler imaging. Each site was assigned a blood flow waveform score (BFS) as follows: 0 = normal arterial flow in muscle; 1 = elevated diastolic flow; 2 = high-resistance flow waveform with retrograde diastolic flow.Results-MTrPs appeared as focal, hypoechoic regions on 2D US, indicating local changes in tissue echogenicity, and as focal regions of reduced vibration amplitude on VSE, indicating a localized stiff nodule. MTrPs were elliptical in shape, with a size of 0.16 ± 0.11 cm 2 . There were no significant differences in size between A-MTrPs and L-MTrPs. Sites containing MTrPs were more likely to have higher TIS compared to normal myofascial tissue (p<0.002). Small arteries (or enlarged

Photoacoustic imaging is an emerging imaging modality that is based upon the photoacoustic effect. In photoacoustic tomography (PAT), the induced acoustic pressure waves are measured by an array of detectors and used to reconstruct an image of the initial pressure distribution. A common challenge faced in PAT is that the measured acoustic waves can only be sparsely sampled. Reconstructing sparsely sampled data using standard methods results in severe artifacts that obscure information within the image. We propose a modified convolutional neural network (CNN) architecture termed Fully Dense UNet (FD-UNet) for removing artifacts from 2D PAT images reconstructed from sparse data and compare the proposed CNN with the standard UNet in terms of reconstructed image quality.

Objectives The purpose of this study was to determine whether the physical properties and vascular environment of active myofascial trigger points associated with acute spontaneous cervical pain, asymptomatic latent trigger points, and palpably normal muscle differ in terms of the trigger point area, pulsatility index, and resistivity index, as measured by sonoelastography and Doppler imaging. Methods Sonoelastography was performed with an external 92-Hz vibration in the upper trapezius muscles in patients with acute cervical pain and at least 1 palpable trigger point (n = 44). The area of reduced vibration amplitude was measured as an estimate of the size of the stiff myofascial trigger points. Patients also underwent triplex Doppler imaging of the same region to analyze blood flow waveforms and calculate the pulsatility index of blood flow in vessels at or near the trigger points. Results On sonoelastography, active sites (spontaneously painful with palpable myofascial trigger points) had larger trigger points (mean ± SD, 0.57 ± 0.20 cm2) compared to latent sites (palpable trigger points painful on palpation; 0.36 ± 0.16 cm2) and palpably normal sites (0.17 ± 0.22 cm2; P < .01). Analysis of receiver operating characteristic curves showed that area measurements could robustly distinguish between active, latent, and normal sites (areas under the curve, 0.9 for active versus latent, 0.8 for active versus normal, and 0.8 for latent versus normal, respectively). Doppler spectral waveform data showed that vessels near active sites had a significantly higher pulsatility index (median, 8.3) compared to normal sites (median, 3.0; P < .05). Conclusions The results presented in this study show that myofascial trigger points may be classified by area using sonoelastography. Furthermore, monitoring the trigger point area and pulsatility index may be useful in evaluating the natural history of myofascial pain syndrome.