МЕДИЦИНСКАЯ ВИЗУАЛИЗАЦИЯ МЯГКИХ ТКАНЕЙ С ПОМОЩЬЮ МРТ

Soft tissues (muscles, tendons, ligaments, adipose tissue, fascia) are affected by a wide range of pathological conditions, including malignant and benign tumors, inflammatory and infectious processes, traumatic injuries, and degenerative changes. Magnetic resonance imaging (MRI) is the method of choice for evaluating soft tissue lesions due to its high contrast resolution and capability for multiplanar imaging [1,2]. Soft tissue sarcomas account for approximately 1% of all malignant neoplasms in adults [4]. Infectious soft tissue involvement, including abscesses and complicated inflammatory processes, also requires high-precision imaging for differential diagnosis and treatment planning [5,6].

In clinical practice, MRI is used when sarcoma is suspected, in the assessment of the musculoskeletal system after trauma, in cases of suspected infectious processes, and for monitoring treatment response [1,4]. Compared with computed tomography, MRI provides more accurate differentiation of soft tissue structures and does not involve exposure to ionizing radiation [3]. International guidelines (ACR Appropriateness Criteria) emphasize the appropriateness of MRI as a first-line modality when a soft tissue tumor is suspected [3].

Physical and Technical Foundations of Soft Tissue MRI

The principle of MRI is based on detecting signals from hydrogen nuclei within a strong magnetic field, followed by excitation with radiofrequency pulses. Image quality is determined by magnetic field strength (typically 1.5–3 T), gradient system performance, and the use of multi-channel receiver coils [2,16]. For soft tissue visualization, the key contrast mechanisms are T1 and T2 relaxation. T1-weighted images provide high anatomical detail and clear visualization of fatty tissue, whereas T2-weighted sequences are sensitive to increased fluid content (edema, inflammation, necrosis) [1,2]. Proton density (PD) sequences allow more precise evaluation of ligaments and tendons [2]. Fat-suppressed techniques (STIR, spectral fat-sat) significantly enhance diagnostic sensitivity in inflammatory and tumor processes [6,9]. STIR provides homogeneous fat signal suppression and is widely used in suspected myositis and infiltrative processes.

Functional techniques further expand the diagnostic capabilities of MRI. Diffusion-weighted imaging (DWI) and ADC maps enable assessment of tissue cellularity. Reduced ADC values are characteristic of malignant tumors, whereas abscesses demonstrate marked diffusion restriction [7,8,11]. Dynamic contrast-enhanced MRI (DCE-MRI) allows analysis of tumor microcirculation and quantitative assessment of perfusion parameters, which is important in soft tissue sarcomas [9,12]. Magnetic resonance spectroscopy (MRS) is used to detect metabolic changes, including elevated choline peaks in malignant neoplasms [10,13]. Modern accelerated imaging technologies (Compressed SENSE, accelerated EPI sequences) reduce examination time without substantial loss of diagnostic value [14,15]. In addition, hybrid techniques (PET/MR) and machine learning algorithms for MRI image analysis are actively developing [17,18].

Protocols and Optimization for Clinical Tasks

The standard MRI protocol for soft tissue imaging includes multiplanar T1- and T2-weighted sequences with fat suppression [1,2].

Recommended sequence set for evaluation of soft tissue tumors:

• T1-weighted images (TR 400–700 ms; TE 10–20 ms) – anatomical assessment and identification of fatty components;
• T2-weighted images (TR >2000 ms; TE 60–100 ms) – detection of edema and cystic changes;
• PD or PD-FS sequences – evaluation of tendon and fascial structures;
• STIR or T2-FS – identification of inflammatory changes;
• Contrast-enhanced T1-weighted imaging after gadolinium administration – assessment of tumor vascularity and aggressiveness [4,9,12].

DWI is performed with b-values of 0 and 800–1000 s/mm² for differentiation between tumors and abscesses [7,8]. DCE-MRI is conducted with a temporal resolution of 5–10 seconds for 3–5 minutes following bolus contrast administration [12]. In traumatic injuries, T2/STIR sequences with fat suppression are preferred for detecting tears and edema. Infections and abscesses are characterized by hyperintense signal on T2/STIR images with peripheral contrast enhancement; DWI assists in confirming the diagnosis [5,8].

Table 1.

Recommended MRI protocols for common clinical scenarios

Note: The parameters provided are indicative and require adaptation to the specific MRI scanner (1.5 T or 3 T), clinical task, and anatomical region. To minimize artifacts (motion, metallic implants), the use of respiratory gating, increased slice thickness, or accelerated sequences is recommended when necessary.

Modern Advances and Techniques

In recent years, quantitative and multiparametric approaches have been actively developed in soft tissue imaging. Diffusion-weighted MRI (DWI) has demonstrated the ability to complement standard morphological sequences. The use of apparent diffusion coefficient (ADC) maps enables differentiation between highly cellular malignant tumors and benign lesions. According to reviews and clinical studies, reduced ADC values correlate with increased cellular density in sarcomas [7,11]. Sun et al. showed that DWI can effectively differentiate soft tissue abscesses from tumors, demonstrating statistically significant differences in ADC values [8]. The development of quantitative diffusion analysis, including multicomponent models such as intravoxel incoherent motion (IVIM), allows separation of true diffusion and perfusion components, thereby expanding the potential for noninvasive assessment of vascularity without contrast administration [9].

Dynamic contrast-enhanced MRI (DCE-MRI) is used for parametric evaluation of tumor vascular characteristics. Perfusion curves and quantitative parameters (including K^trans and V_e) enable assessment of microcirculation and vascular permeability, which are relevant for sarcoma grading and prognostic evaluation of tumor aggressiveness [9,12]. Elevated K^trans values are associated with higher malignancy grades in soft tissue tumors [12].

Magnetic resonance spectroscopy (MRS) identifies metabolic features of tissues. An increased choline peak is characteristic of malignant tumors, whereas lipomas demonstrate predominance of lipid signals [10,13]. Although clinical use remains limited, MRS is considered a potential additional biomarker of tumor activity.

Hybrid PET/MR imaging combines metabolic information (FDG-PET) with the anatomical detail of MRI. According to Massaro et al., PET/MR provides more accurate localization of tumor foci and improved evaluation of soft tissue components compared with PET/CT [17].

In recent years, artificial intelligence and deep learning techniques have been increasingly implemented for automated segmentation and classification of soft tissue lesions. The review by Litjens et al. demonstrates high accuracy of deep learning algorithms in medical imaging tasks, including oncologic applications [18].

Table 2.

Contemporary Studies in Soft Tissue MRI

Practical Recommendations and Limitations

When performing soft tissue MRI, both absolute and relative contraindications must be considered, including incompatible implants, uncertified metallic devices, and severe claustrophobia. According to musculoskeletal MRI protocol recommendations, the type of implant and its MRI compatibility should be assessed prior to the examination [16]. Gadolinium-based contrast enhancement is indicated when a tumor or inflammatory process is suspected; however, caution is required in patients with impaired renal function. Assessment of glomerular filtration rate (GFR) is mandatory before contrast administration, particularly in at-risk patients [12]. The literature also discusses the issue of gadolinium deposition in tissues after repeated examinations, necessitating a balanced and justified approach to contrast use [12].

Metallic orthopedic implants may produce significant magnetic susceptibility artifacts. To minimize these effects, dedicated artifact-reduction sequences, frequency adjustments, and distortion-correction techniques are applied [14,16]. Motion artifacts remain one of the main technical challenges in soft tissue MRI. These can be reduced by limb immobilization, respiratory gating, shortened protocols, and accelerated sequences [15,16]. In the evaluation of muscle fatty degeneration, it is essential to differentiate bone marrow signal (hyperintense on T1-weighted images) from pathological fatty infiltration of muscle tissue. In such cases, fat-suppressed sequences (STIR, FS) are mandatory [1,2].

Diagnostic errors may occur when interpreting vascular anomalies, organized hematomas, or post-traumatic changes, which may mimic tumor masses [6]. In doubtful cases, dynamic contrast-enhanced imaging, MR angiography, or follow-up examinations are recommended [9,12]. Fibrotic changes and scar tissue are characterized by low signal intensity on T2-weighted images and minimal or absent contrast enhancement, helping differentiate them from tumor recurrence [4]. To improve diagnostic accuracy, standardized terminology and structured reporting are recommended, including specification of lesion location, size, signal characteristics, contrast enhancement pattern, and signs of invasion [3]. Optimal interpretation is achieved through a multidisciplinary approach involving radiologists, oncologists, and orthopedic specialists, particularly in suspected sarcoma or complex inflammatory conditions [4].

Conclusion

Soft tissue MRI is a versatile and highly informative diagnostic modality, providing both detailed anatomical visualization and functional assessment of pathological processes. The combination of standard T1- and T2-weighted sequences with fat suppression, diffusion-weighted imaging, and dynamic contrast enhancement allows effective differentiation of tumor, inflammatory, and traumatic changes [1,7,12].

Modern technological advances—including high-field scanners, multi-channel coils, accelerated protocols, and artificial intelligence techniques—have significantly expanded the diagnostic capabilities of MRI [14,15,18]. Despite its high sensitivity and specificity, MRI has limitations related to examination duration and susceptibility to artifacts. Rational protocol planning and careful consideration of the clinical context are key factors in maximizing diagnostic value. Thus, the appropriate application of multiparametric MRI, combined with clinical data, ensures accurate diagnosis and contributes to optimization of treatment strategies in patients with soft tissue diseases.