Q2-With the help of suitable diagrams explain the generation of action

potential in a cell.
Ans-Certain types of cells within the body, such as nerve and muscle cells
are encased in a semipermeable membrane that-permits some substances
to pass through the membrane while others are kept out. Surrounding the
cells of the body are the body fluids. These fluids are conductive solutions
containing charged atoms known as ions. The principal ions are sodium
(Na+), potassium (K+), and chloride (C-). The membrane of excitable cells
readily permits entry of potassium and chloride ions but effectively blocks
the entry of sodium ions. There are two conditions of penetration of
membrane by sodium ions, first concentration of sodium ions inside the
cell becomes much lower than in the intercellular fluid outside. Since the
sodium ions are positive, this would tend to make the outside of the cell
more positive than the inside. Second, in an attempt to balance the electric
charge, additional potassium ions. Due to charge imbalance there a
potential generate that called resting potential of the cell and this state of
cell is known polarized state. This approx. -60 to -100mv. This movement
of sodium ions into the cell constitutes an ionic current flow that further
reduces the barrier of the membrane to sodium ions outside and at the
same time potassium ions, which were in higher concentration inside the
cell during the resting state, try to leave the cell but are unable to move.as
rapidly as the sodium ions. As a result, the cell has a slightly positive
potential on the inside due to the imbalance of potassium ions This
potential is known as the action potential and is approximately + 20 mV. A
cell that has been excited and that displays an action potential is said to be
depolarized; the process of changing from the resting state to the action
potential is called depolarization.

Q8 Describe the principle of generation of X-Rays and their utilization

for medical applications. Highlight the working of X-rays machine with
a block diagram.
Ans-X rays are generated when fast-moving electrons are suddenly
decelerated by impinging on a target. An X-ray tube is basically a high-
vacuum diode with a heated cathode located opposite a target anode. This
diode is operated in the saturated mode with a fairly low cathode
temperature so that the current through the tube does not depend on the
applied anode voltage. The intensity of X rays depends on the current
through the tube. This current can be varied by varying the heater current,
which in turn controls the cathode temperature. The wavelength of the X
rays depends on the target material and the velocity of the electrons hitting
the target. It can be varied by varying the target voltage of the tube.
Working-There are two part of the circuit-
➢ One is producing high voltage which is applied to the tube’s anode and
cathode.
➢ The current through the tube follows the HT pathway and measured by
an mA meter.
➢ KV selector switch facilitates change in voltage between exposures.
Voltage is measured with the help of KV meter.
➢ Exposure switch control the timer and thus the duration of application
of KV
➢ To compensate the main supply voltage (220) in voltage there a
compensator used in circuit.
➢ The second part of the circuit have control of heating x-ray tube filament

➢ Filament temperature is heated with 6-12 v of ac supply at a current of

3-5 amp.
➢ The filament temperature can control by vary the current hence there a
ma switch selector attached.

Q. What are the desirable characteristics of transducer used in

biomedical application? Also discuss the problem encountered during
measurement of physiological variables.
Ans- •RANGE :The range of an instrument is generally considered to
include all the levels of input amplitude and frequency over which the
device is expected to operate.
•SENSITIVITY: The sensitivity of an instrument determines how small a
variation of a variable or parameter can be reliably measured. This
determines the resolution of the device, which is the minimum variation
that can accurately be read.
•LINEARITY: The degree to which variations in the output of an instrument
follow input variations is referred to as the linearity of the device.
•HYSTERESIS: Hysteresis is a characteristic of some instruments where
by a given value of the measured variable results in a different reading when
reached in ascending direction from that obtained when it is reached in a
descending direction.
•FREQUENCY RESPONSE: The frequency response of an instrument is its
variation in sensitivity over the frequency range of the measurement. An
instrument system should be able to respond rapidly enough to reproduce
all frequency components of the waveform with equal sensitivity.
•ACCURACY: Accuracy is a measure of systemic error.(Error due to
tolerance of electronic component, mechanical error due to meter
movement, error due to poor frequency response)
•SIGNAL TO NOISE RATIO: It's a ratio of signal power to noise power and
it should be as high as possible. In hospital environment, generally power
line noise acts an interference.
•STABILITY: stability is the ability of a system to resume a steady state
condition following a disturbance at the input rather than be driven into
uncontrollable oscillation.
•SIMPLICITY: All systems and instruments should be as simple as possible
to eliminate the chance of component or human error.
problem encountered during measurement of physiological variables:-
1. inaccessibility of variables to measurement
2. variability of data
3. lack knowledge about interrelationships
4. interaction among physiological systems
5. effect of transducer on the measurement
6. Artifacts
7. Energy limitations
8. Safety consideration
Biological effect of ultrasound: - The biological effects of ultrasound refer
to the potential adverse effects the imaging modality has on human tissue.
These are primarily via two main mechanisms: thermal and mechanical.
Thermal effects Due to the law of the conservation of energy, all of the
sound energy attenuated by tissues must be converted to other forms of
energy. The majority of this is turned into heat. As such, it is possible for
ultrasound to raise tissue temperature by up to 1.5°C. For sensitive tissues
(eg. fatal) this rise in temperature may have deleterious effects if present for
an extended period of time. The thermal index (TI), is the ratio of the power
produced by the transducer to the power required to raise a tissue in the
beam by 1°C.
Mechanical effects :the mechanical bioeffect of ultrasound refers to
damage caused by the actual oscillation of the sound wave on tissue. The
most common is referred to as cavitation and is caused by the oscillation
of small gas bubbles within the ultrasound field. In certain circumstances,
these bubbles may grow in size or collapse generating very high energies to
adjacent tissue. This can increase tissue temperature. The mechanical
index (MI) is a value that attempts to quantify the likelihood of cavitation
by an ultrasound beam. This value is readily displayed on the ultrasound
screen and it is recommended that it is kept below 1.9 to remain safe.
MRI: -Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging
technique used to visualize the internal structures of the body, particularly
soft tissues like the brain, muscles, and organs. It uses strong magnetic
fields and radio waves to create detailed images without the need for
ionizing radiation (unlike X-rays or CT scans).
Working: 1. Magnetic Field: The MRI machine generates a strong
magnetic field, usually 1.5 to 3 Tesla (T), which causes the hydrogen atoms
in the body (primarily in water molecules) to align with the magnetic field.
2. Radio Frequency Pulse: The MRI machine sends a brief radio frequency
(RF) pulse into the body. This pulse disturbs the alignment of hydrogen
atoms, causing them to absorb energy and move to a higher energy state.
3. Signal Detection and Image Creation: The MRI sensors (or coils) detect
the RF signals emitted as the hydrogen atoms return to their original state.
The signals are then processed by a computer to construct detailed images
of the internal structures. Different tissues (such as fat, muscle, and fluid)
emit different signals due to their varying hydrogen content and relaxation
times.
4. Image Contrast: MRI images are generated based on differences in the
signals from different tissues, with varying levels of contrast.T1 weighted
images,T2-weighted images.