D Glossary
title: D Glossary
description: Introduces common terminology
| English Term | Explanation |
|---|---|
| k-space | In MRI, refers to the original frequency domain data matrix collected, through which images are generated by Fourier transform. |
| T1-weighted | A contrast method of MRI sequences, emphasizing longitudinal relaxation characteristics, with clear structure. |
| T2-weighted | Another contrast method of MRI sequences, emphasizing transverse relaxation characteristics, with obvious display of liquid/edema. |
| Windowing (Window Width/Level) | In CT or X-ray image display, used to adjust grayscale range and midpoint to optimize contrast. |
| Flat-field correction | Corrects dark spots or streak artifacts in images caused by detector/illumination non-uniformity or inconsistent response. |
| SENSE (Sensitivity Encoding) | MRI parallel imaging technique that uses multiple coil sensitivity information to achieve scanning acceleration. |
| Parallel Imaging | Uses multiple receiving coils to sample simultaneously to reduce scanning time or improve resolution. |
| Echo Time (TE) | The time interval between RF pulse and signal acquisition start in MRI, affecting image contrast. |
| Repetition Time (TR) | The pulse cycle interval time in MRI, affecting signal recovery and contrast. |
| Flip Angle | The tilt angle of nuclear magnetic resonance caused by MRI radio frequency pulse, affecting signal intensity/contrast. |
| Field of View (FOV) | The anatomical region or volume size covered by imaging, usually expressed in mm. |
| Voxel | 3D pixel, the smallest unit in medical imaging data. |
| Slice Thickness | The thickness of each image in tomographic scanning (CT/MRI), affecting volume reconstruction and partial volume effect. |
| Partial Volume Effect | When a voxel contains multiple tissue types, signal mixing leads to reduced accuracy. |
| Artifact | Non-real tissue structures in images introduced by equipment, patient movement, signal processing, etc. |
| Signal-to-Noise Ratio (SNR) | The ratio of signal intensity to noise intensity in an image, measuring image quality. |
| Contrast-to-Noise Ratio (CNR) | The ratio of signal difference between lesion and background tissue to noise, reflecting recognizability. |
| Reconstruction Kernel | The filter type used during CT reconstruction, which affects sharpness and noise level. |
| Radiomics | Extracting large amounts of quantitative features (texture, shape, intensity, etc.) from images for modeling and analysis. |
| Segmentation | Classifying image pixels/voxels into different structures (such as organs, edema, tumors) for quantitative analysis. |
| Registration | Aligning images from different time points or different modalities to the same space for convenient comparison. |
| Deep Learning | Using deep neural networks (such as CNN, Transformer) to analyze/predict image data. |
| Transfer Learning | Applying a model trained on one task to another related task to reduce training costs. |
| Multimodal Learning | Fusing multiple imaging modalities (such as MRI + PET + genetic data) for joint analysis. |
| Overfitting | The phenomenon where a model performs well on training set but has poor generalization ability on new data. |
| Dice Coefficient | A metric that measures the degree of overlap between predicted and real regions in segmentation tasks. |
| Intersection over Union (IoU) | Used for segmentation evaluation: the ratio of the intersection of prediction and real regions to their union. |
| Sensitivity (Recall) | The proportion of true positives correctly identified in classification tasks. |
| Specificity | The proportion of true negatives correctly identified. |
| ROC Curve | A curve showing the relationship between false positive rate and true positive rate, used for classification evaluation. |
| Hounsfield Unit (HU) | Unit representing tissue density in CT: water is 0, air is approximately -1000. |
| Contrast Agent | Injected or taken before imaging to enhance contrast of certain tissues or blood vessels. |
| Dual-energy CT | Using two different energies of X-rays to contrast and enhance imaging material discrimination capability. |
| Ground-glass Opacity (GGO) | Mildly increased opacity in lung images where vascular texture is still visible. |
| Mass | Larger volume (usually >3 cm) possibly abnormal structure or tumor, requiring observation and differentiation. |
| Nodule | Smaller volume (usually ❤️ cm) structure, requiring follow-up for growth or malignancy. |
| Pleural Effusion | Fluid accumulation in the pleural cavity, appearing as fluid level or blurred boundary in images. |
| Cardiomegaly | Increased cardiothoracic ratio, suggesting cardiac structural abnormalities. |
| Calcification | Calcium deposition in tissues or lesions, visible as high density in CT or X-ray. |
| Infarct | Tissue necrosis caused by interrupted blood supply, with typical imaging manifestations in MRI/CT. |
| Ring Enhancement | In contrast-enhanced images, lesion edge enhancement with low signal/low density center, common in metastatic tumors or brain abscesses. |
| Spiculated Margin | Tumor edge with radiating spiky protrusions, suggesting invasiveness or malignancy. |
| Ghosting | Particularly in the phase encoding direction in MRI images, streaks or duplicate images caused by patient movement, etc. |
| Flip Angle | The tilt angle of nuclear magnetic resonance caused by MRI radio frequency pulse, affecting signal intensity/contrast. |
| Fourier Transform | Mathematical transformation that converts spatial domain signals to frequency domain (such as k-space to image domain). |
| Coil Sensitivity | Response differences of multi-channel MRI receiving coils at different spatial positions, used for parallel imaging. |
| Nyquist Frequency | Half of the lowest necessary sampling frequency in sampling theory, below which aliasing will occur. |
| Aliasing | When sampling is insufficient or FOV is too small, signals outside the image are repeated or overlapped in the image. |