Spatial resolution in screen-film mammography is about how finely details can be distinguished, and it is expressed in line pairs per millimeter (lp/mm). In conventional screen-film systems, the practical limit is around 15 lp/mm because the image blur comes from several unavoidable sources: the finite size of the x-ray focal spot creates geometric blur, the screen-film interface adds detail loss, and imperfect contact between screen and film plus processing steps further degrade sharpness. Motion during exposure can worsen this, but the most influential factor is the overall blur built into the system, which caps how much detail can be resolved. So describing resolution with lp/mm and a practical ceiling near 15 lp/mm aligns with how these systems perform in typical practice. Other statements aren’t accurate because resolution is indeed tied to image sharpness, it isn’t realistic for standard equipment to reach 50 lp/mm, and resolution isn’t determined solely by exposure time—many geometric and processing factors set the limit.

In PET imaging with FDG, the amount of glucose the brain uses reflects neuronal activity. During an active seizure, the affected brain region has markedly increased neuronal firing and energy demand, so it shows focal hypermetabolism (increased glucose uptake) on the scan. This is why the sign of an active seizure is increased glucose uptake in the seizured area. Seizure-free or baseline function would not show this ictal hypermetabolism, and decreased uptake would indicate reduced metabolic activity (often seen interictally or after a seizure), not an ongoing ictal event.

Brachytherapy. It uses sealed radioactive sources placed directly into tissues, body cavities, or on the surface of the body. Placing the sources close to the tumor delivers a high radiation dose to the target while the dose falls off quickly with distance, helping spare surrounding healthy tissue. The sources are sealed to prevent leakage, and placement can be interstitial (into tissue), intracavitary (within a body cavity), or surface-based (as molds or applicators). In contrast, external beam approaches deliver radiation from outside the body with machines like linear accelerators, and the Gamma Knife cobalt-60 setup, though using sealed sources, delivers beams from outside rather than implanting sources inside the patient.

RF pulses excite hydrogen nuclei in a strong magnetic field, which is the hallmark of MRI. The pulse tips the net magnetization away from alignment with the main field, depositing energy into the tissue. After the pulse, the protons relax back to their resting state and emit signals that are captured by coils. The rate at which they relax (T1 and T2) varies among tissues, and MRI uses different sequences and gradient fields to convert these relaxation properties into images with contrast. This mechanism—using radiofrequency energy to manipulate and detect hydrogen nuclei—sets MRI apart from other imaging modalities: ultrasound relies on sound waves, CT on X-ray attenuation, and PET on radioactive tracer decay. So the principle described is used by MRI.