I thought it would be useful to start with some definitions of few basic terms used during scanning to allow the candidate to improve his or her understanding of the subject and improve technique. This section is not meant to give a comprehensive description of the physics involved. It would be useful to dwell in each heading and get as much information out of it as possible and use it to improve your practice.
Some basic scientific facts to know
Ultrasound denotes sound >20000 cycles / second [>2000 Hz] which is beyond the sonic range
One Hertz is the number of sound wave cycles or pulses / second
Wavelength is the time it takes to complete one cycle
Frequency is the number of cycles in a fixed period of time
The average speed of sound in soft tissue 1540 m/s
Amplitude is the range of vibration measurement from the baseline to the peak
Attenuation is the reduction in the amplitude and intensity of the beam when passing through tissues
Diagnostic ultrasound range is 2-20 Mega Hz
Terminology and Function
Overall gain:
Controls the brightness of the whole image
Dynamic range:
Number of gray shades displayed in the image and helps in tissue identification
Output power:
The amount of pressure the sound is producing at tissue level
TGC:
Time gain compensation varies the gain up or down in certain depths of the 2D image and compensates for attenuation of brightness in the selected area
Distal enhancement:
Entails increased reflection from the distal part of the examined structure
Shadowing:
Entails the reduction of echoes distal to the organ
Resolution
axial resolution
lateral resolution
Indicates the ability to separate separate close objects parallel to the sound beam
To improve axial resolution increase the pulse repetition rate
Indicates the ability to separate separate close objects perpendicular to the sound beam
Multiple focal zones give better lateral resolution but slow the frame rate
Further Terminology
anechoic or sonolucent indicates a tissue devoid of any echoes [simple cyst]
hypoechoic indicates low level echoes like a lymph node
isoechoic means similar to the surrounding tissues
hyperechoic or echogenic means brighter intensity compared to the surrounding
homogeneous indicates smooth gray densities with no focal areas of different echo texture
heterogeneous means mixed densities probably due to different tissue types.
General rules
All organs should be examined for location, shape, size, texture, range of motility, relation to other organs and abnormal pathology
Each organ should be examined in at least two orthogonal planes
Use the gain, power and different setup for different types of tissues and resolution to get the best picture.
Normal and abnormal findings should be labelled and all pictures should include the date, patient's name, date of birth and orientation
A permanent record should be kept in the case not
Safety measures
You must be aware of the guidelines for the safe use of diagnostic ultrasound equipment published by the British Medical Ultrasound Society and any new upgrades when applicable.
Use the lowest power to start with and change the setting as necessary.
Always check the thermal index [TI] and mechanical index [MI] in your machine and keep them to the lowest level possible.
Ultrasound scanning should not be used for social reasons or to create pritty pictures
Make sure that the patient is not allegic to latex or the gel before you start.
The term ALARA should be in the back of your mind at all times to keep the power level and exposure time as low as reasonably achievable.
Objectives of gynaecological scanning
Identify normal position, size, shape and texture of pelvic organs
Recognise the physiological changes that occur in them during the cycle
Recognise and describe any changes in these normal characteristics
Relate any change to the various known gynaecological conditions
Use the technique to extend the clinical judgment necessary for patients care.
Indications for gynaecological scanning
The most common indications for gynaecological scanning are:
abnormal uterine bleeding
acute and chronic pelvic pain
ovarian cyst / pelvic mass
fertility scanning including monitoring ovulation and testing the fallopian tubes
early pregnancy dating and monitoring of complications
