Okay, let's tackle this question. The patient is middle-aged and has sudden left upper and lower limb motor weakness for 30 minutes. The question is about the best imaging modality to plan treatment.

First, the core concept here is acute stroke. When someone has sudden motor deficits, especially in both upper and lower limbs on one side, it's likely a stroke. The key is to determine if it's ischemic or hemorrhagic because treatment differs. For ischemic stroke, rapid intervention is crucial, like thrombolysis or thrombectomy, while hemorrhagic requires a different approach.

The correct answer should be the imaging modality that can quickly differentiate between these two. CT scan is typically the first choice in the ER because it's fast and widely available. It can show if there's a hemorrhage, which is critical because CT is better at detecting acute bleeding compared to MRI. However, MRI, especially diffusion-weighted imaging (DWI), is more sensitive for early ischemic changes. But in an acute setting where speed is essential, CT is preferred initially. So the answer is likely CT head.

Now, the options: Let's say the options are A. MRI, B. CT, C. Ultrasound, D. X-ray. Then B is correct. The other options are incorrect. MRI is not first-line due to time and availability. Ultrasound isn't suitable for brain imaging. X-ray doesn't show brain pathology. The clinical pearl here is that CT is the initial imaging for acute stroke to rule out hemorrhage before thrombolytic therapy. So the correct answer is B. CT scan.

**Core Concept**
Acute unilateral motor deficits in both upper and lower limbs suggest a stroke, necessitating rapid differentiation between ischemic and hemorrhagic etiologies. Imaging must detect early ischemic changes and exclude intracranial hemorrhage to guide treatment like thrombolysis.

**Why the Correct Answer is Right**
**CT scan (Computed Tomography)** is the first-line imaging modality for acute stroke due to its speed, availability, and ability to detect hemorrhage. While MRI is more sensitive for early ischemia, CT is preferred initially in emergency settings to rule out contraindications (e.g., bleeding) before administering thrombolytics. Non-contrast CT can identify hypodense infarcted tissue and hyperdense arterial thrombi within minutes of symptom onset.

**Why Each Wrong Option is Incorrect**
**Option A: MRI** – Though MRI (especially diffusion-weighted imaging) detects ischemia earlier than CT, it is less accessible in emergencies and cannot distinguish acute bleeding as effectively.
**Option C: Ultrasound** – Cranial ultrasound lacks resolution for cerebral imaging and is not used for stroke assessment.
**Option D: X-ray** – Plain skull X-rays do not visualize brain parenchyma or vascular changes relevant to stroke.

**Clinical Pearl / High-Yield Fact**
Never administer thrombolytics without a CT scan to exclude intracranial hemorrhage. "Time is brain" in stroke: CT is the gold standard for initial evaluation in acute settings.

**Correct Answer: B. CT scan**

✓ Correct Answer: A. CT scan of the head