US vs CT

US vs CT

Multi-slice CT is increasingly replacing ultrasonography (US) for the evaluation of patients with acute abdominal pain
CT has major advantages over US: it is extremely fast and its time burden is often less than that of a US examination .
CT is not disturbed by gas and bone, while obesity is even an advantage.
Most of all, CT is not operator-dependent and can be reviewed by others, even at a distance.
With all these advantages, it is not surprising that US is losing field in the evaluation of the acute abdomen.
US however has some advantages.

advantages of US:

• US does not require ionizing radiation, which can be important in younger patients and pregnant women.
• The spatial resolution of a high-frequency US image is higher than that of a CT image.
  This is only true if the target organ can be approached closely, which requires either a thin patient or the use of graded compression.

स्थानिय स्रोत परिचालन गरि टिष्टुङ स्वास्थ्य चौकी मकवानपुरमा संचालन हुँदै गरेको "गर्भवती महिलाहरुको लागि नि:शुल्क भिडियो एक्स-रे सेवा कार्यक्रम" अन्तर्गत शिशुको मुटुको धड्कन मोनिटर गर्ने क्रममा ....photo courtesy: Sagar Lama

What is Ultrasound?

What is Ultrasound?

Sound is a physical phenomenon that transfers energy from one point to another. In this respect, it is similar to radiation. It differs from radiation, however, in that sound can pass only through matter and not through a vacuum as radiation can. This is because sound waves are actually vibrations passing through a material. If there is no material, nothing can vibrate and sound cannot exist.

One of the most significant characteristics of sound is its frequency, which is the rate at which the sound source and the material vibrate. The basic unit for specifying frequency is the hertz, which is one vibration, or cycle, per second. Pitch is a term commonly used as a synonym for frequency of sound.

The human ear cannot hear or respond to all sound frequencies. The range of frequencies that can be heard by a normal young adult is from approximately 20 Hz to 20,000 Hz (20 kHz). Ultrasound has a frequency above this range. Frequencies in the range of 2 MHz (million cycles per second) to 20 MHz are used in diagnostic ultrasound. Ultrasound is used as a diagnostic tool because it can be focused into small, well-defined beams that can probe the human body and interact with the tissue structures to form images.

What is Transducer?
The transducer is the component of the ultrasound imaging equipment that is placed in direct contact with the patient's body. It performs several functions as will be described in detail later. It's first function is to produce the ultrasound pulses when electrical pulses are applied to it. A short time later, when echo pulses return to the body surface they are picked up by the transducer and converted back into electrical pulses that are then processed by the system and formed into an image.