Cooperative Patent Classification


CPC Definition - Subclass A61N

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Last Updated Version: 2017.08
ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B 18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infra-red radiators for heating H05B)
Definition statement

This place covers:

Specially adapted apparatus, instruments, devices, or processes for the following types of therapy:

  • electrotherapy, e.g. iontophoresis;
  • magnetotherapy;
  • radiation therapy;
  • ultrasound therapy.

Components having specialized structural features that limit their use to the apparatus, instruments, or devices for the types of therapy appropriate for this subclass.

Relationships with other classification places

Several subclasses provide for subject matter that is used for therapy. The relationship between these subclasses in regard to the type of therapy covered by each is as follows:

Subclass A61N provides for medical treatment-type therapy by apparatus or methods utilizing forms of energy other than direct mechanical energy when they are not used for surgical purposes and they are intended to either

  • destroy, control, or advance the recovery of sick or abnormal cells within body tissue while minimizing undesirable destruction of adjoining healthy cells, or
  • treat other types of abnormal conditions of the body (e.g., disease, impaired organ, injured limb).

In particular, subclass A61N covers implanted devices, when the implanted device is not a replacement or supplementation of an actual portion of the organ or part, utilizing forms of energy other than direct mechanical energy to stimulate organs or body parts in a manner that facilitates, regulates, or improves their normal functioning.

Subclass A61H provides for massage and physical-type therapy apparatus or methods for the treatment of disease or disability (i.e., an abnormal condition of the body) by utilization of direct mechanical energy. The apparatus or methods appropriate for this subclass do not surgically alter any portion of the bodies during treatment. Usually, the massage and therapy apparatus and methods of this subclass are intended to facilitate the healing of diseases, reduce the impact of injuries, or beneficially influence the condition of disabled body parts by physically moving a part of a body (e.g., devices for exercising a passive body member) solely by direct physical contact with, or stimulation of, external surfaces of the body or naturally occurring cavities in the body. However, stimulation of internal organs or body parts, such as artificial respiration and stimulation of the heart, when it is done by direct mechanical energy is also considered proper for this subclass.

Subclass A61K and Subclass A61P provide for drug-type therapy using chemical compounds or medicinal preparations specially adapted for use in healing, benefiting, or destroying abnormal conditions of the body (e.g., diseases, birth defects) and the specific therapeutic activities that the chemical compounds and medicinal preparations are used for.

Subclass A61B provides for surgery and surgical-type therapy that alters or repairs organs and body parts. It also provides for any surgical or diagnostic apparatus or methods that would otherwise be proper for subclass A61H or A61N when the apparatus or methods are used for both purposes or combined together. In particular, subclass A61B provides for surgical instruments, devices, or methods for transferring non-mechanical forms of energy to or from the body (e.g., electromagnetic radiation surgery) to alter or repair it.

References
Limiting references

This place does not cover:

Apparatus for diagnosis or surgery combined with, or applicable also as, therapy apparatus

Apparatus for radiation diagnosis

Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body (e.g., radiation surgery, electro-surgery)

Instruments, implements, tools, or methods specially adapted so as to limit their use to only animals

Apparatus or methods utilizing direct mechanical energy in therapy intended to treat disease or disability

Percussion or vibration massage apparatus (e.g. using supersonic vibration)

Apparatus or methods for stimulating specific reflex points by heating or cooling within the cell-life limits

Devices for applying radioactive material to the body

Informative references

Attention is drawn to the following places, which may be of interest for search:

Measuring bioelectrical signals of the body or body parts

Surgical accessories

Artificial substitutes or replacements for parts of the body

Heating or cooling appliances for medical or therapeutic treatment

Saunas

Radiopharmaceuticals

Anaesthetic apparatus in general

Artificial hearts and circulatory assistance means intended for implantation

Pressure infusion pumps

Devices or methods to cause a change in the state of consciousness by mechanical, optical or acoustical means, e.g. audiovisual stimuli

Therapeutic chemical compounds or medicinal preparation used to treat sicknesses or abnormal conditions of the body

A61P

Measurement of nuclear X-radiation

Techniques for handling of particles or electromagnetic radiation

Incandescent lamps having general utility

Infrared radiators for heating

Electrotherapy; Circuits therefor (A61N 2/00 takes precedence; irradiation apparatus A61N 5/00)
Definition statement

This place covers:

Details about electric fields which directly provide a therapeutic effect or which render the delivery of therapeutic substances possible; details about (components of) apparatuses which generate these electric fields.

References
Limiting references

This place does not cover:

High frequency currents for surgery instead of therapy (i.e. higher temperatures so as to destroy tissue instead of healing tissue)

Informative references

Attention is drawn to the following places, which may be of interest for search:

Irradiation apparatus

Measuring blood pressure / blood flow

Measuring blood output from heart

Detecting specific parameters of the ECG cycle

Detecting muscle signals

Detecting urogenital signals

Detecting gastrointestinal signals

Measuring electrical impedance of a portion of the human body

Measuring movement of the entire body or parts thereof

Diagnosis using ultrasound in general

Measuring blood pressure by ultrasound

Measuring blood flow by ultrasound

Gastric anti-eating devices using electrical stimulation

Devices implantable in the eye e.g. ocular inserts

Devices for eye surgery

Mechanical stimulation of ear nerves

Heart stimulation by mechanical means

Stimulating specific reflex points using electric currents

Percussion or vibration massage with electrotherapy

Acoustically, mechanically or optically inducing sleep or relaxation

Electrically conditioning the air e.g. by ionising

Applying static electricity for purifying the air

Computer-assisted medical diagnosis or treatment

Recognising signal patterns per se

Deaf aid sets

Special rules of classification

Additional information could be either

  • specific details about components, signals or algorithms which are not related to the invention as such; or
  • less preferred embodiments which are shortly mentioned (e.g. inventive specification of cochlear implants which can be used for retinal implants as well).

Documents with such information should be given an Indexing Code.

Synonyms and Keywords

In patent documents, the following abbreviations are often used:

AAI

single chamber atrial pacemaker with inhibited mode

AED

automatic external defibrillator

AEI

atrial escape interval

AV

atrioventricular

AVD

atrioventricular delay

AVI

atrioventricular interval

BPM

beats per minute

CHD

coronary heart disease

CHF

chronic heart failure

CO

cardiac output

CRT

cardiac resynchronisation therapy

DBS

deep brain stimulation

DDD

biventricular pacemaker e stimulation rate with dual mode

DDDR

DDD pacemaker with pacing rate dependent on sensor output

DDI

biventricular pacemaker with inhibited mode

ECG

electrocardiogram

EKG

electrocardiogram

HR

heart rate

ICD

implantable cardioverter defibrillator

IMD

implantable medical device

IPG

implantable pulse generator

NS

neural stimulation

PAVB

post-atrial ventricular blanking

PESP

postextrasystolic potentiation

PMT

pacemaker mediated tachycardia

SV

stroke volume

SVT

supraventricular tachycardia

VDD

pacemaker that senses the atrium and ventricle and paces the ventricle with dual mode

VF

ventricular fibrillation

VT

ventricular tachycardia

VVI

single chamber ventricular pacemaker with inhibited mode

Electrodes {(electrosurgical electrodes A61B 18/14)}
Definition statement

This place covers:

Details about the electrodes and their associated leads specially adapted for delivering electrical therapeutic stimulation.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Patient's garment with incorporated electrodes for medical monitoring

Electrodes specially adapted for ECG

Electrodes specially adapted for EEG

Electrodes specially adapted for EMG

Electrodes for electrosurgery

Stents and instruments for their placement

Stimulating specific reflex points using electric currents

Anchoring by balloon expansion

Form details about flexible conductors per se

Form details about conductors for implantation in a human body

Special rules of classification

Details about the stimulating device as such, about the therapeutic signal and/or about the stimulating algorithm should be classified in A61N 1/36-A61N 1/3712.

Arrangements or circuits for monitoring, protecting, controlling or indicating {(for external stimulators A61N 1/3603; for implantable neurostimulators A61N 1/36128; for heart stimulators A61N 1/37; for defibrillators A61N 1/3925)}
Definition statement

This place covers:

Protecting the functioning of electrical therapeutic stimulation devices, especially against MRI.

This group only relates to protection (especially against MRI) for electrical therapeutic stimulation devices and not for other types of medical devices such as drug pumps. The purpose of this protection is to protect the functioning of the medical device.

References
Limiting references

This place does not cover:

For external stimulators

For implantable neurostimulators

Monitoring or protecting for heart stimulators

Monitoring or protecting for defibrillators

Informative references

Attention is drawn to the following places, which may be of interest for search:

Neutralising atmospheric radiation

Mattresses for protecting against e.g. static electricity or radiation

Dynamisation and other esoteric therapies using medicinal preparations obtained by wave energy

NMR gyrometers

Measuring electric variables

Instruments for measuring magnetic variables involving magnetic resonance

Provisions within MR facilities for enhancing safety during MR

Control of generator output per se

Screening of apparatus or components against electric or magnetic fields

Special rules of classification

Protecting the functioning of the medical device constitutes the difference with A61N 1/16, which relates to protecting the human body. E.g. pacemaker circuitry protecting the pacemaker from the field of a TV antenna should go to A61N 1/08 whereas as special building arrangement for protecting a person from the same field to A61N 1/16.

Synonyms and Keywords

In patent documents, the following abbreviations are often used:

MR

magnetic resonance

MRI

magnetic resonance imaging

NMR

nuclear magnetic resonance

{Magnetic resonance imaging [MRI] compatible leads}
Definition statement

This place covers:

Leads (both implantable and external) having features that mitigate the effects of unwanted electric currents induced by a Magnetic Resonance Imaging [MRI] device or field.

Screening or neutralising undesirable influences from {or using,} atmospheric or terrestrial radiation or fields {(using atmospheric electricity or earth currents H05F 3/00)}
Definition statement

This place covers:

Screening or neutralising atmospheric or terrestrial radiation or fields with the purpose of protecting the human body. The purpose of this protection is to protect the human body.

References
Limiting references

This place does not cover:

Electrostimulators protected for electromagnetic interference

Informative references

Attention is drawn to the following places, which may be of interest for search:

Measuring magnetic field characteristics of the earth

Carrying-off electrical charges using atmospheric electricity or earth currents

Special rules of classification

Protecting the human body constitutes the difference with A61N 1/08, which relates to protecting the functioning of the medical device. E.g. pacemaker circuitry protecting the pacemaker from the field of a TV antenna should go to A61N 1/08 whereas as special building arrangement for protecting a person from the same field to A61N 1/16. A61N 1/08 takes precedence over A61N 1/16.

for stimulation
Definition statement

This place covers:

Details about the therapeutic signal and/or about the stimulation algorithm, constructional and/or circuitry details, telemetry details.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Details about the electrodes or the leads

Applying constant continuous current

Electromedical belts

Electromedical brushes, combs, massage devices

Inteference currents

Iontophoresis

Promoting growth of cells

Electroporation

Improving skin appearance

{Cancer treatment, e.g. tumour}
Definition statement

This place covers:

Covers devices (both implanted and external to the body) that treat cancer by electrical stimulation.

{Control systems}
Definition statement

This place covers:

Covers features of control systems used by electrical stimulation devices that are external to the body (e.g. switches/buttons used for controlling TENS devices, control displays for pain relief devices, controlling modes of operation for muscle stimulators, algorithms/flow charts for controlling external stimulation devices, etc.).

{using physiological parameters for adjustment}
Definition statement

This place covers:

Device control systems under A61N 1/3603, which adjust therapeutic electrical stimulation based upon at least one sensed physiological parameter.

{specified by the stimulation parameters}
Definition statement

This place covers:

Device control systems under A61N 1/3603, which are characterised by their stimulation parameters (e.g. frequency, amplitude, pulse width, multiphasic, combination of waveforms, etc.).

{of the outer, middle or inner ear}
Definition statement

This place covers:

Covers therapeutic devices that electrically stimulate portions of a patient’s outer, middle, or inner ear.

{Cochlear stimulation}
Definition statement

This place covers:

Devices under A61N 1/36036 that electrically stimulate a patient’s cochlea.

{fitting procedures}
Definition statement

This place covers:

Devices and methods used for fitting a patient with a cochlear stimulation device or setting a cochlea stimulation parameter (as described in A61N 1/36038) (This subgroup is intended for devices having more than a general mention of fitting or stimulation parameters).

{for correcting spinal deformities, e.g. scoliosis}
Definition statement

This place covers:

Electrical stimulation devices used for correcting spinal deformities.

{Spinal stimulation}
Definition statement

This place covers:

Includes implantable neurostimulation devices and associated methods used to perform spinal stimulation (as described in A61N 1/3605).

{based on impedance measurement}
Definition statement

This place covers:

Control systems for implantable neural stimulation devices (under A61N 1/3605) which measure impedance (This subgroup is intended for devices having more than a general mention of impedance).

{in combination with non-electric therapy}
Definition statement

This place covers:

Heart stimulation devices (e.g. pacemakers) under (A61N 1/362) which also include an additional non-electric therapy to the heart or other body area (e.g. drug therapy, nanotherapy, gene therapy, etc.).

{for stimulating the heart at multiple sites of the ventricle or the atrium}
Definition statement

This place covers:

Heart stimulation devices under A61N 1/368, which include dual chamber pacemakers (e.g. pacers using DDD modes of operation) and pacing devices that electrically stimulate multiple sites within the 4 chambers of the heart.

{Multi-site stimulation in the same chamber}
Definition statement

This place covers:

Covers heart stimulation devices under A61N 1/3684 having more than one stimulation site within the same heart chamber (e.g. two stimulation electrodes in the right ventricle that deliver separate and/or different stimulation to each electrode, etc.).

{Bi-ventricular stimulation}
Definition statement

This place covers:

Covers heart stimulation devices which stimulate both the right ventricle [RV] and the left ventricle [LV].

Arrangements in connection with the implantation of stimulators
Definition statement

This place covers:

Specifications going beyond the implantable medical device in isolation, such as communicating with, delivering power to, or testing of the implantable medical device.

Structural details of (parts of) the implantable medical device, e.g. casing or feedthrough.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Details about leads and electrodes

Transmitting measured data to processing apparatus

Transferring electromagnetic energy to implanted prostheses

Transferring data to implanted prostheses

Materials for catheters

Materials for coating of implanted articles

Testing electrical condition of batteries per se

Computer assisted treatment

GUI for local control of medical devices

Telemedicine: remote diagnosis, remote control of instruments

Transmitting signals with a radio link per se

Sealing of leads to lead-through insulators per se

Feedthrough capacitors per se

Batteries per se

Manufacture of small size batteries per se

Electrical connections per se

Electrical connections for medical use

Adapters for connecting two parts per se

Electrical connectors for medicine and surgery

Charging batteries per se

Charging batteries by inductive or capacitive coupling

Near-field (inductive) transmission systems per se

Radio transmission systems per se

Transmission of digital information per se

Transmitting circuits using pulse with modulation or pulse position modulation

{Pacemaker or defibrillator security, e.g. to prevent or inhibit programming alterations by hackers or unauthorised individuals}
Definition statement

This place covers:

Devices and methods used to provide security (both programming and physical) for electrical stimulation devices (in particular pacemakers and defibrillators) to combat hackers and other unauthorised persons from accessing/re-programming electrical stimulation devices.

{Pacemakers}
Definition statement

This place covers:

Covers device features related to the construction of pacemakers (i.e. housings/can details, material, shape, etc.).

{Brain implants}
Definition statement

This place covers:

Covers device features related to the construction of brain implants (i.e. housing or can details, material, shape, etc.).

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Burr Hole Covers

{Intravascular implants}
Definition statement

This place covers:

Covers device features related to the construction of intravascular implants (i.e. housing details, material, shape, etc.).

{Anchoring of the implants, e.g. fixation}
Definition statement

This place covers:

Covers anchoring/fixation details of electrical stimulation devices.

for producing shock effects
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Electrolytic capacitors per se

For producing shock effects per se

Synonyms and Keywords

In patent documents, the following abbreviations are often used:

AF

atrial fibrillation

VF

ventricular fibrillation

{External heart defibrillators [EHD]}
Definition statement

This place covers:

Covers external heart defibrillators (e.g. Automatic External Defibrillators [AEDs], semi-automatic external defibrillators, manual) and methods for constructing and using them.

{in combination with cardiopulmonary resuscitation [CPR] therapy}
Definition statement

This place covers:

External defibrillators and methods for using them for performing or assisting in cardiopulmonary resuscitation [CPR] therapy.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Cardiopulmonary Resuscitation [CPR] therapy

{User protection from shock}
Definition statement

This place covers:

External defibrillators which include features that protect a user or patient from an accidental or unwanted shock.

{in combination with another heart therapy}
Definition statement

This place covers:

Implantable defibrillator which in addition to electrical shock therapy, also provides another form of heart therapy (e.g. drug therapy, gene therapy, nanotherapy, etc.).

{Pacing therapy}
Definition statement

This place covers:

Implantable defibrillators under A61N 1/3962 which apply pacing therapy in addition to defibrillation shocks.

{Pain reduction therapy}
Definition statement

This place covers:

Implantable defibrillators under A61N 1/3962 which apply electrical stimulation therapy for pain reduction.

Applying ionised fluids {(ion generators H01J 37/00)}
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Baths for special therapeutic purposes

Baths for specific parts of the body

Ionised inhalator

Ion generators

Generating ions into the atmosphere

Magnetotherapy
Definition statement

This place covers:

Use of static or dynamic magnetic fields for treating humans or animals, where the magnetic field itself provides the therapeutic effect.

References
Limiting references

This place does not cover:

Using a magnetic field for diagnosis

Medicinal preparations obtained with a magnetic field

Releasing a medicament through the use of a magnetic field

Radiation therapy (ultrasound therapy A61N 7/00; devices or apparatus applicable to both therapy and diagnosis A61B 6/00)
Definition statement

This place covers:

Therapeutic treatment of the human or animal body with electromagnetic or particle radiation.

Therapy implies the curing of a disease or malfunction of the body and includes prophylactic treatment like killing of germs, bacteria in or on the body by means of radiation as well as treatment of symptoms like pain (anaesthesia) by means of radiation.

References
Limiting references

This place does not cover:

Magnetotherapy

Ultrasound therapy

Radiation imaging or diagnosis

Surgery with radiation (cf. special rules below)

Treatment by heat, sauna

Sterilization or disinfection of articles or products by radiation

Lighting

Irradiation devices for articles or products

Lithography with a particle beam

Ion implantation in semiconductors

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Devices or apparatus applicable to both therapy and diagnosis

Informative references

Attention is drawn to the following places, which may be of interest for search:

Radiation measurement devices, dosimeters, beam monitors

Accelerator Technology

X-ray tubes

Beam transport, forming, focussing, filtering

Radiation Shielding

Protection of tissue around treatment site

Site contact feedback, abutting means

Patient positioning

Patient movement or breathing monitoring

Markers

Navigation, image assistance

Sensing at the treatment site

Photosensitizers, radiosensitisers

Radionuclides, radiopharmaceuticals

Radiation sources

Vapour or discharge lamps, tubes

Light guides

Filters

LEDs

Lasers

Psychological treatments

Acupuncture

Teeth whitening by light

Curing resins within the teeth

Medical informatics, patient data management

Devices for implanting pellets or seeds

(Balloon) catheters

Balloons for catheter applicators

Irradiation of blood outside the patient (ex-vivo)

Special rules of classification

The IPC group A61M36/00 is not used: these devices are instead classified in A61N 5/10, since their purpose is therapeutic.

Surgery vs. Therapy

In contrast to the therapeutic applications covered by this group, surgery is characterized by the immediate and direct destruction or transformation of the tissue (ablation, vaporization, coagulation...). For therapy, the effect in the tissue is induced with rather lower intensity and power levels and/or longer pulse durations (photothermal, photochemical reactions, biostimulation...). Thus, for instance, cell destruction by photoactivation of an agent is to be classified in A61N 5/062. Some devices may be used for both applications depending on the operation mode.

Note that A61N 5/1084 covers focussed radiotherapy applications like "gamma knife" and stereotactic radiotherapy which are sometimes also called "radiosurgery", which is not to be confused with surgery in the sense of A61B 18/00.

Light therapy (A61N 5/06)

The scheme in A61N 5/06 contains several independent classification trees covering different aspects of a light therapy apparatus.

The therapeutic application is meant to be classified in A61N 5/0613 and lower hierarchical groups thereof for external treatments or A61N 5/0601 and lower hierarchical groups thereof for internal treatments.

Further aspects are then classified in codes according to the area of treatment (subgroups of A61N 2005/0635), the type of light source used (subgroups of A61N 2005/065), and the wavelength of therapeutic light (subgroups of A61N 2005/0658).

Aspects like coherence of the therapeutic light (A61N 2005/067) and polarisation (A61N 2005/073) are also to be coded.

For some aspects, no suitable code is available and in such cases, sometimes the scheme of a neighbouring field is used: subgroups of A61B 2018/00773 or A61B 2017/00022 (feedback at the treatment site), A61B 2018/2255 (features at the distal end of a light guide, e.g. diffusers).

Note: devices of A61N 5/0614 (tanning) do not need to be classified in A61N 2005/0661 since the ultraviolet light is there by necessity.

Particle and X-ray therapy (A61N 5/10)

In the A61N 5/10 part, there is a similar aspect coded in A61N 2005/1085 (type of particles, e.g. ions, electrons, neutrons, low energy photons etc.). This code is obligatory for the particles specified in the subgroups of A61N 2005/1085. Only normal energy (MeV) photons are not coded in this tree, since it concerns the default situation.

The group A61N 5/01 should not be used for radiotherapy gantries, since a rotating gantry is common and not worth to classify.

Synonyms and Keywords

In patent documents, the following abbreviations are often used:

IMRT

Intensity Modulated Radiation Therapy

IMAT

Intensity Modulated Arc Ttherapy

IGRT

Image Guided Radiation Therapy

MLC

Multileaf Collimator

SAS

Step And Shot

(O)LED

(Organic) Light Emitting Diode

DRR

Digitally Reconstructed Radiograph

SOBP

Spread-Out Bragg Peak

DVH

Dose Volume Histogram

EPI

Electronic Portal Imaging

OAR

Organ At Risk

Ultrasound therapy (lithotripsy A61B 17/22, A61B 17/225; massage using supersonic vibration A61H 23/00{; using ultrasound for introducing media into the body A61M 37/0092})
Definition statement

This place covers:

Ultrasound therapy of the human or animal body. Also included is the thermal destruction of tissue in the focal point of a high intensity ultrasound beam.

References
Limiting references

This place does not cover:

Removal of calculi, thromboses etc. by ultrasound

Extracorporeal shock waves (with mainly mechanical effect, e.g. lithotripters)

Cutting using ultrasonic vibrations, e.g. with vibrating knife

Devices creating a mechanical shock wave by laser light

Apparatus for introducing media into the body using ultrasonic waves, phonophoresis

Informative references

Attention is drawn to the following places, which may be of interest for search:

Ultrasound diagnosis

Accessories for surgery or diagnosis

Ultrasound imaging during surgical procedures

Percussion or vibration massage

Generating mechanical vibrations

Transmitting, conducting and directing sound in general

Special rules of classification

Ultrasound therapy with negligible thermal effect. Treatment area not reduced to a focal point. E.g. devices for bone fracture healing.

The subgroups define various application areas on the body to be treated or therapeutic applications. Headgroup A61N 2007/0004 not to be used for classification.

Localized ultrasound hyperthermia, high intensity focused ultrasound (HIFU). The effect is primary a thermal one of substantially heating tissue above the normal temperature or even above the point of tissue destruction. Mechanical percussion to destroy calculi is to be classified in A61B 17/22004 or A61B 17/225 in case of external shockwaves.

Intracavitary localized hyperthermia. The probe or transducer is located within a body cavity.

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

HIFU

high intensity focused ultrasound

Phased array transducer

transducer consisting of an array of small transducers individually adressable with a time delay to steer the focal point of the beam