Overview

Magnetic Resonance Imaging (MRI) uses powerful magnetic fields and radio waves to generate images of organs and tissues inside the body. Unlike X-rays or CT scans, MRI does not use ionizing radiation. The MRI machine contains a strong magnet that creates a powerful magnetic field, typically ranging from 1.5 to 3 Tesla. This magnetic field aligns the hydrogen nuclei in the body's water molecules. Once the hydrogen nuclei are aligned, the machine sends radiofrequency pulses to temporarily disturb this alignment. When the pulses are turned off, the hydrogen nuclei return to their original state, emitting radiofrequency signals in the process. These emitted signals are detected by the MRI machine and used to construct images of the body's internal structures. MRI provides non invasive high-resolution images of soft tissues, making it particularly useful for imaging the brain, spinal cord, muscles, ligaments, and other soft tissues. In addition, It is possible to use intravenous contrasts agents to obtain higher contrast in specific tissues. (1)

Applications in clinical Dermatology

In dermatology, MRI is used primarily to evaluate skin conditions and diseases that involve deeper tissue structures not visible with other imaging techniques.

MRI in Malignant Skin Tumors (3)

Assessment of Soft Tissue Lesions: While MRI is not typically used for initial diagnosis—often made through biopsy or visual inspection—it helps distinguish between benign and malignant lesions based on their tissue characteristics and extent (Table1).

Preoperative Planning: MRI provides detailed images of a lesion’s size, depth, and local extent, particularly for skin lesions that extend beyond the surface and involve deeper tissues such as subcutaneous fat and muscle. It also illustrates the lesion's relationship to surrounding tissues, including potential invasion of nerves, lymphatics, or blood vessels. This information is crucial for planning complex surgical procedures, especially for large or deep tumors

Monitoring Tumor Response: MRI is used to track how skin tumors respond to treatments such as chemotherapy, radiation, or targeted therapies. It is effective in assessing changes in tumor size and structure over time.

Evaluation of Melanoma: MRI can be used to assess the local extent of melanoma and to identify any regional or distant metastases. It is particularly helpful in evaluating the involvement of lymph nodes and other distant sites and if perineural invasion is suspected.

Evaluation of NMSC (non-melanoma skin cancer): MRI should be considered for locally advanced disease, or if there is suspicion of perineural invasion, nodal or distant metastases.

Table 1 - Characteristic MRI findings of malignant skin tumors (3).

MRI in Assessment of Inflammatory Skin Conditions:

1. Hidradenitis Suppurativa- MRI is used for the detection, characterization, and measurement of tunnels in the perianal region. It supports surgical planning, particularly in patients with perianal involvement. (5)

2. Morphea- valuable diagnostic tool for detecting and monitoring musculoskeletal involvement. It can reveal features such as fascial thickening, articular synovitis, tenosynovitis, and subcutaneous septal thickening. Follow-up imaging with MRI can show treatment effects and disease progression. (2)

MRI in Evaluation of Congenital Anomalies

MRI is helpful in assessing congenital cutaneous malformations and vascular anomalies, such as hemangiomas and vascular malformations. (6)

Advantages and limitations of MRI in skin analysis (4)

• Non-Invasive Technique that allows for distinguishing diseased tissues from surrounding normal tissues.

• Spatial Resolution: While MRI may not offer the highest spatial resolution for evaluating skin compared to other methods, it provides detailed anatomical and biochemical information about the skin. MRI is excellent for assessing deeper structures but might not deliver the fine detail needed for superficial skin lesions, where techniques like dermoscopy or confocal microscopy might be more suitable.

• Resolution Limits: Resolution in MRI is influenced by involuntary patient motion or physiological motion (e.g., blood pulsation, breathing, swallowing, eye movement) which can significantly decrease effective resolution. Avoiding patient motion to achieve resolutions below 0.1 mm is virtually impossible. Consequently, the reasonable MRI resolution for human in vivo imaging is close to 0.1 mm.

• Expensive and may not be as readily available as other imaging modalities, such as ultrasound or CT.

Experimental Applications in Dermatology (1)

• Skin Hydration: MRI allows in vitro examination of water mobility in the skin and transdermal shunts. High-field MRI and in vitro Nuclear Magnetic Resonance (NMR) microscopy are employed to study skin hydration effects, product efficacy, and water mobility in skin layers. Gradient at Right Angles to Field (GARField) MRI provides high spatial resolution for detailed imaging of skin layers and moisture content.

• Biochemical Characterization: MRI aids in analyzing the skin's biochemical profile, including collagen content and hydration levels.

• Drug and Product Penetration: MRI assesses the penetration and distribution of cosmetic products, offering insights into their effectiveness and the interaction between water and lipids in the skin.

• Skin Vascularization: MRI can measure skin vascularization in both normal and pathological conditions.

  
  

References

(1). https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1468-3083.2010.03588.x

(2). https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/srt.13410

(3). https://link.springer.com/article/10.1186/s13244-022-01205-8

(4). https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1468-3083.2010.03588.x

(5). https://pmc.ncbi.nlm.nih.gov/articles/PMC9340234/

(6). https://pmc.ncbi.nlm.nih.gov/articles/PMC6732108/