MRI uses two main sequences: T1-weighted and T2-weighted. T1 shows anatomy, T2 detects pathology. T1 uses short TR (400-600ms) and TE (10-20ms). T2 uses long TR (3000-6000ms) and TE (90-110ms)
MRI sequences are radiofrequency pulses creating images with specific appearances. Sequences are categorized by dominant tissue influence: PD, T1, T2, diffusion, flow, and others. Signal intensity describes tissue appearance: white (high), grey (intermediate), black (low)
Sesamoids are embedded in tendons to protect them from injury. Accessory ossicles are supernumerary bones derived from unfused ossification centres. Most common sesamoids are hallucal, lesser metatarsal and interphalangeal joint. Accessory ossicles include os trigonum, os peroneum and os naviculare
CNR measures contrast between tissue of interest and background. SNR measures image signal relative to background noise. Optimal images have reasonable noise level. Quantum noise (mottle) is inherent in x-ray and CT imaging
MRI images are generated using water molecule diffusion patterns. Diffusion is not random but reflects interactions with obstacles. Water molecules move faster along axons and slower perpendicular to them
CT uses X-rays to create detailed images of organs and tissues. MRI employs radio waves and magnets to generate body images. Both methods require patients to lie still in doughnut-shaped devices