13.07: memory

Introduction to Memory in Ultrasound Systems

  • Overview:

    • The discussion centers around the memory circuits within ultrasound systems and their functions.

    • Memory is critical for storing echo signals and building images in ultrasound diagnostics.

Components of an Ultrasound System

  • Diagram of Ultrasound Components:

    • Previously covered components include:

    • Pulses

    • Power control

    • Transducer

    • Beam former including transmit focusing, receive focusing, apodization

  • Receiver Processes:

    • Involved processes:

    • Amplification

    • Compensation

    • Compression

    • Demodulation

    • Rejection

Function of Memory

  • Importance of Memory:

    • Stores amplitude and location of each echo signal received.

    • Each echo's location is assigned a specific address in memory where its amplitude is stored.

    • Memory facilitates the construction of ultrasound images by combining stored echoes.

  • Memory Structures:

    • Memory Matrix: An arrangement of address locations that store echo data.

    • Think of it like a checkerboard, where each square represents an address location.

    • Address Locations:

    • Store the echo amplitude at respective locations.

    • Each address location corresponds to a pixel in the displayed image.

    • Pixels = Picture Elements.

Types of Memory in Ultrasound

  • Historical Context:

    • Earlier systems referred to memory as scan converters converting vertical into horizontal information.

  • Digital Process:

    • Modern ultrasound systems utilize digital memory rather than analog.

    • Synonymous terms include "memory" and "digital scan converter."

  • Dimensions of Memory Matrix:

    • A matrix can be structured simply (e.g., 10x10) for illustrative purposes but is significantly larger in real applications.

    • Illustrative example: 10x10 = 100 pixels.

Storage of Echo Amplitudes in Memory

  • Example of Echo Storage:

    • For an echo with amplitude of 25 units stored in a specific address based on range.

    • Subsequent echoes (e.g., 37 microvolts, 14 units, and 32 units) follow the same pattern.

    • Illustrates how echoes are stored sequentially across multiple scan lines.

  • Sequential Scanning:

    • Each scan line contributes to building the full image.

    • Images consist of a series of address locations where echo amplitudes are recorded.

Matrix Size and Bit Depth

  • Matrix Size:

    • Essential for determining image resolution.

    • Typical ultrasound matrix sizes:

    • 512x512 (roughly 250,000 total address locations)

    • 1024x1024 (roughly 1 million pixels)

  • Bit Depth:

    • Defines how many values or shades of gray can be represented per pixel.

    • Example for typical ultrasound systems:

    • 8 bits = 256 shades of gray.

    • More bits provide more shades and improve contrast resolution.

Bit Depth Examples

  • Shades of Gray Scenarios:

    • 1 bit: 2 shades (black and white)

    • 2 bits: 4 shades

    • 3 bits: 8 shades

    • 4 bits: 16 shades

    • 5 bits: 32 shades

    • 6 bits: 64 shades

    • 7 bits: 128 shades

    • 8 bits: 256 shades

    • 9 bits: 512 shades

    • 10 bits: 1024 shades

Digital Memory Characteristics

  • Total Bits Calculation:

    • Formula: Total Bits = Number of Pixels × Bit Depth

    • Example: For 1 million pixels and 8 bits per pixel = 8 million bits.

  • Memory Size in Bytes:

    • Conversion: Total Bits / 8 = Total Bytes.

    • Example: 8 million bits = 1 million bytes or 1 megabyte.

Important Digital Terminology

  • Bit:

    • Abbreviation for binary digit (0 or 1).

  • Byte:

    • A collection of 8 bits.

  • Kilobyte (KB):

    • Approx. 1024 bytes.

  • Megabyte (MB):

    • Approx. 1024 KB, or about 1 million bytes.

  • Gigabyte (GB):

    • Approx. 1024 MB, or about 1 billion bytes.

  • Terabyte (TB):

    • Approx. 1024 GB, or about 1 trillion bytes.

  • RAM vs. ROM:

    • RAM: Random Access Memory (Volatile)

    • ROM: Read-Only Memory (Non-volatile)

Practical Application and Implications

  • File Size for Ultrasound Images:

    • Single grayscale ultrasound images estimated to be around 1 MB. Often compressed for storage and retrieval.

  • Quality and Size Correlation:

    • Larger matrix sizes improve resolution but increase file size.

    • Increasing bit depth enhances contrast resolution but also increases file size.