The MANCHESTER handbook of ppt

The MANCHESTER handbook of ULTRASOUND TECHNIQUES THE MANCHESTER HANDBOOK OF ULTRASOUND TECHNIQUES ‘The most important part of a stethoscope is the bit between the ear-pieces.’ - Samuel Oram, consultant cardiologist and describer of Holt-Oram syndrome A beginner’s guide and vade-mecum for first and second year specialist registrars in diagnostic radiology. Written and edited by: Brennan Wilson, Consultant Paediatric Radiologist, Manchester Children’s Hospitals Hari Mamtora, Consultant Radiologist, Hope Hospital, Salford Jane Hawnaur, Senior Lecturer and Consultant Radiologist, Manchester Royal Infirmary Note to readers, wherever you are: This booklet is a joint effort. We want it to be as good as possible. We expect to have to make several revisions of the book, and all constructive comments, drawing our attention to inaccuracies and omissions etc., will be gratefully received. Brennan Wilson Department of Radiology Royal Manchester Children’s Hospital Pendlebury Manchester M27 4HA Tel: (0161) 794 4696 (switch) (0161) 727 2204 (direct) (0161) 727 2460 (fax) email: Brennan.Wilson@man.ac.uk Introduction This handbook is designed for first and second year specialist registrars in radiology . It assumes a basic understanding of ultrasound physics and technology, and the rudiments of cross-sectional anatomy, and is designed to help you from that background towards the practical business of working an ultrasound machine. You will find a summary of the main controls of an ultrasound machine, and points of anatomy where these are directly relevant to orientating yourself within a given image. Pathology is mentioned where it is relevant to how an image is taken. However, this is not meant to replace a textbook of any of these subjects. So far, the booklet reflects the collected experience of the three editors with valued comments from some colleagues and current SpRs (notably Ralph Jackson). However, it is admittedly still experimental and would obviously benefit from as many constructive comments as possible. We do not know of another such handbook being available, and we realise that we may have committed omissions and errors of fact, and we have also almost certainly failed to realise some of the things that SpRs find difficult to grasp at first. With that in mind: • It is printed on one side of the paper only, in order to encourage you to add your own notes. We would very much like to collect as many of the booklets as possible at the end of the year, in order to be able to use these comments to re-edit the book. We will be glad to make arrangements to give the originals back to you if you like. • Please feel free to send any comments you have to me - anonymously if you like - or to the electronic comment board for the registrars at www.smuht.man.ac.uk/radio. We honestly want to use the readers of this book as a resource for improving it year by year. Remember, the success of the teaching for the junior SpRs depends on you yourselves! BW Contents 1 Principles of ultrasound scanning 2 Gynaecology and obstetrics 3 Hepatobiliary imaging 4 Renal tract 5 Lower limb venous duplex imaging and colour Doppler of the neck 6 Small parts Chapter 1: Principles of ultrasound scanning Approach to the patient The same professional courtesy is expected in the ultrasound examination room as anywhere else in medicine. • Greet your patient by name, introduce yourself, shake hands, smile, and make eye contact. • Most patients will understand what ultrasound is but you should be ready to explain it to patients with poor understanding (e.g. children) or if you are going to perform a more complicated procedure, e.g. an ultrasound-guided interventional procedure. • Protect the patient’s clothing with paper and warn them about the cold US gel. Respect the patient’s modesty and be alert to any signs of tenderness as you apply the transducer. • Avoid discussing one patient in front of another. • You may make a serious diagnosis in the patient’s presence in the ultrasound room. Ensure that you understand local and national guidelines on communicating bad news to patients, and be honest, courteous and sympathetic. Approach to the ultrasound machine • Stand or sit comfortably in front of the machine so that you can reach the patient without bending sideways unnecessarily. • Check that the appropriate transducer is connected and that the system is set up for the type of examination you wish to perform, e.g. 3.5 MHz sector probe and abdominal protocol. • Use sufficient acoustic coupling gel, especially in hairy patients. • Hold the transducer with the tips of your right thumb and fingers. This is important as it allows you to roll the probe around its long axis. • Arrange the transducer wire so that its weight does not drag on the hand holding the probe. You may want to untangle it or loop it around the back of your neck. • If necessary, rest your right forearm or elbow on the patient’s couch or a convenient part of his body. Ask his permission first. General principles of ultrasound imaging • Make sure you are familiar with the machine before you start. • Unlike the situation with plain radiography, in ultrasound there is no-one else to adjust the settings of the machine to produce an excellent image. The machine settings should be adjusted to suit you . • Each ultrasound image should be optimised to illustrate a particular clinical sign. Don’t try to show too much on a single image - take two if each will show one particular finding more clearly. • Remember that what you see is a tomogram. If you are examining any organ with a definite volume, you need to sweep across the plane of the scan all the way from one side of the organ to the other to make sure you have missed nothing. Then you need to repeat the sweep in at least one other plane. You find the other planes by rotating the probe or approaching the organ from another angle. • Get into the habit of sweeping smoothly through an organ at a steady rate. Then tubular structures within the organ such as blood vessels will appear to move steadily along their courses, whereas rounded structures such as masses will be easy to notice as they flash into view and out again. • Label and hard-copy standard views of normal organs examined. Obtain views in several planes, labelled and annotated with measurements if appropriate. Take extra views to show any abnormal findings. Your colleagues may have to use these images for future comparisons, so try to include as much visual information as you can on the hard copy record of your examination. • Many abdominal organs may be obscured by bowel gas. One way round this problem is to press firmly against the bowel for a few minutes, and literally squeeze the bowel out of the way (the graded compression technique ). Ask your patient’s permission before you do it, and desist if you are requested. Ultrasound machine settings and their meanings The parameters preset on the machine will enable you to start scanning but use the following information to help you understand the controls and modify settings to obtain the best diagnostic image in individual patients. Images are viewed from the patient’s right for longitudinal scans, and from the patient’s feet for transaxial scans. • Transducer frequency is the frequency of the signal emitted. On some modern machines this can be selected electronically from a range within the same transducer: however, nowadays most transducers are still single-frequency only and you will have to toggle between transducers or plug a new one in to the socket on the front or side of the machine. High frequency probes have a better longitudinal resolution but less penetrating power through tissues, and are typically used for children and small organs or ones close to the transducer face. Low frequency probes can be used to penetrate deep into large areas such as adult abdomens but at the cost of a somewhat lower resolution. • Transmit power is the level of power delivered into the body, given on a logarithmic scale. Use the lowest transmit power necessary for diagnosis. If you need to increase the transmit power to see far into the image, consider choosing a transducer at a lower frequency instead. • Gain is the amplification applied to the returning signal. It needs to be set so that the signals in the area of interest are all contained within the grey scale on the screen. Common mistakes here are to allow the back of the image to become too dark, e.g. when examining the back of a large liver, or to allow structures seen behind a fluid cavity (for example, the adnexae behind the urinary bladder) to become too bright in the acoustic enhancement. • Receive gain is the overall amplification applied, and has the effect of changing the brightness of the whole image. • Time gain compensation (gain curve, swept gain) : This compensates for acoustic loss in the deeper tissues from absorption, scatter and reflection of the US beam. The aim is to show structures of the same acoustic strength as echoes of equal amplitude, whatever their depth. On most modern machines, the control is presented as a column of slides, each of which governs the amplification (gain) at a specific depth within the image, starting from the transducer face at the top. A good deal of swept gain compensation is built into the machine so it is often convenient to start with the slides in a vertical stack, but be ready to adjust them as necessary. • Transmit zone (focal depth) : This is the depth at which the ultrasound beam is at its narrowest after passing through the near zone and before fanning out into the far zone . Thus, the lateral resolution of the image is greatest here. Position it at or just behind the area of interest. Multiple focal zones are applicable to large static structures, but may cause a drop in frame rate, which can make any movement while scanning appear intrusive. • RES (regional expansion selection) : This facility is available on Acuson machines and produces a magnified image in a selected area of interest with increased frame rate and spatial resolution. Keep the RES box in proportion to the sector: e.g., a long and narrow box gives a larger expanded image. You can alter the transmit zone on the expanded image, but not the depth. • Log compression ( dynamic range) : This is the range in acoustic power (in decibels) between the faintest and the strongest signals that can be displayed on the screen. Many machines have a default setting of 48-55 dB. Increasing the dynamic range produces a greyer, flatter image. Decreasing it increases the apparent ‘contrast’ in the image and emphasises small changes in signal strength - this can be helpful where abnormalities are very close to the same shade of grey as the surrounding tissue, for example metastases in the liver or masses in the testis. However, it also increases the visual ‘noise’ on the image. Controls best left alone to start with • Preprocessing is the computer enhancement applied to the returning raw data before it is reformatted into an image. • Persistence (frame averaging) : The number of frames which are mathematically added to produce each image. Higher persistence tends to suppress noise but can cause motion artefacts. • Postprocessing is computer enhancement applied to the reformatted image, for example by compressing some parts of the grey-scale selectively. Unlike the gain and dynamic range controls, it does not affect the overall quantity of information on the image. Common artefacts • Reverberation . Echoes are transmitted to and fro between the transducer and an interface in the patient, e.g. in the fat of the anterior abdominal wall, or gas filled bowel. This produces a ‘ghost’ of the interface responsible at twice the depth, and may be mistaken for pathology. Try looking from a different angle to see what happens to the suspicious echo. • Acoustic shadowing . A user-friendly artefact which allows identification of calculi as strongly reflective structures which do not allow passage of ultrasound energy beyond them. A dark shadow is seen behind a strong echo. Gas in bowel or lung generally produces a less intense acoustic shadowing, or bright ‘comet-tail’ artefacts. • Acoustic enhancement . Passage of ultrasound through a tissue which is less attenuating than usual produces a relative increase in echo amplitude distal to the area, a so called ‘bright-up’. This can help to differentiate fluid-containing cysts from other hyporeflective but solid masses. Remember to adjust the gain if you are looking at structures behind a fluid collection, e.g. behind the bladder. Troubleshooting If your image is poor, a list of possible causes to check through might include: • Machine-related causes: poorly adjusted settings of the depth or overall gain, focusing, transducer transmission frequency, etc. • Technique-related causes: poor contact against the skin, inappropriate acoustic window chosen, etc. • Patient-related causes: image degradation by interposition of obesity, bowel gas, bone, ectopic calcification etc. Try reducing the frequency of the transducer, perhaps as far as 2.5 MHz, to penetrate obesity; reduce the dynamic range, increase persistence to reduce the noise. Some very modern machines offer harmonic imaging which may help to overcome poor signal quality. • Do the best you can, but recommend alternative imaging, e.g. CT, if appropriate. Chapter 2: Transabdominal pelvic ultrasound for gynaecology and obstetrics GYNAECOLOGICAL APPLICATIONS Indications • Pelvic pain or swelling • disturbance of the bladder or bowel function • Change in menstrual pattern (dysmenorrhoea, menorrhagia, abnormal bleeding) • Amenorrhoea or infertility Preparation • Ask the patient to drink two pints (one litre) of fluid one hour before her appointment, to fill her bladder. • Ask about relevant symptoms, the patient’s menstrual cycle, date of her last period, prior pregnancies, contraceptive use, and use of hormone replacement therapy, as appropriate. • With the patient supine, expose the entire abdomen from the xiphisternum to the symphysis pubis. Protect the patient’s clothing with paper. • For a patient of average build, a 3.5-4 MHz phased array transducer is appropriate. Other patients may require a lower frequency, e.g. 2.5 MHz. • Check the adequacy of bladder filling - the bladder fundus should extend to the fundus of the uterus. An overdistended bladder is unpleasant for the patient and displaces structures away from the US probe. Ask the patient to void a little to reduce overdistension. ROUTINE EXAMINATION: Sagittal and parasagittal views of uterus, cervix and vagina. • Sweep through the full length of the uterine body, cervix and vagina from side to side. The normal uterus has a fairly homogeneous medium reflectivity, with brighter echoes from the endometrium and endometrial cavity. • Image a midline sagittal view of the uterus and measure length from fundus to external os. • Approximate uterine lengths are: • Premenarchal girls vary with age, usually less than 2.5 cm, with the cervix the widest part. • Women of reproductive age 6-8 cm with corpus length twice that of the cervix. Uterine size is 1-2cm larger in multiparous compared with nulliparous women and 1-2cm smaller in post-menopausal women. • The uterus can be tilted in any direction so angle the probe if the uterus lies oblique to the midline of the patient. A uterus may be anteflexed (anteverted) (fundus pointing towards anterior abdominal wall)or retroflexed retroverted (pointing towards sacrum). It may have to be measured in two portions. • Image a zoomed sagittal view of the uterus showing the bright central echoes representing the endometrium plus any tissue in the endometrial cavity. The double layer thickness of bright echoes in the AP direction may measure up to 15 mm during the menstrual cycle, but should not exceed 5mm after the menopause. • Intrauterine contraceptive devices produce strong acoustic reflections and acoustic shadowing from within the uterine cavity. Transverse views of uterus, cervix, parametrium and vaginal vault • Sweep through the uterine body, cervix and upper vagina from top to bottom. Image a cross- section of the uterine fundus. Note the orientation of the fundus on the sagittal view and angle your transducer accordingly to obtain a section at right angles to the long axis, anteverted or retroverted. • Measure AP and transverse diameters (approximately 4 cm AP x 5 cm transverse in reproductive years). Transverse and longitudinal views of adnexae • Scan right and left adnexae carefully from the uterus out to the pelvic walls. • Assess the size, shape and position of the ovaries . These usually lie on the pelvic wall, at or above the level of the uterine fundus, on the back of the broad ligament. They are normally ovoid in shape, with mid-level reflectivity and small cystic areas representing developing follicles (in the reproductive age group). If you have difficulty finding the ovaries, use the internal iliac vessels as a guide, the ovaries usually lying medial to the vein. Other favourite hiding places are the pouch of Douglas, behind or above the uterine fundus or adjacent to the cervix. You may need to angle obliquely through the bladder from the far side to obtain clear views of the ovaries. • The dominant (ovum-producing) follicle may measure up to 25mm in diameter, but should regress in the luteal phase of the menstrual cycle. • Ovarian volumes : Volume is estimated by multiplying the anteroposterior, transverse and longitudinal diameters and dividing by 2. • In childhood , size varies with age. Follicles may be seen up to age four from maternal transplacental ovarian stimulation; premenarchal follicles may start to appear from age 8. • In the reproductive years , volumes vary from 6-14 cm 3 . • In post-menopausal women, volumes vary from 1-4 cm 3 . They have no obvious follicles and may be more difficult to see. They should not exceed about 8 cm 3 in volume and obvious asymmetry in size should be considered abnormal. • The broad ligament also contains the fallopian tubes (normally invisible) , uterine and ovarian vessels and supporting ligaments . • The important objective in this circumstance is to exclude ovarian enlargement or an adnexal mass , e.g. hydrosalpinx, cysts, free fluid, remembering to check for masses displaced up out of the pelvis. • Image longitudinal views of the right and left kidneys (q.v.) to exclude renal tract abnormality, such as hydronephrosis or congenital anomaly. Review the retroperitoneum, liver, and peritoneal spaces if appropriate. ENDOVAGINAL ULTRASOUND In endovaginal US the transducer is closer to the organs of interest, allowing higher frequency (5-7.5 MHz) transducers to be used, and higher spatial resolution images to be obtained. The disadvantage is the small range of the probe, so that endovaginal US does not give the same wide view of the pelvis, renal tracts and retroperitoneal regions as transabdominal US; the two techniques are complementary. EVUS overcomes the difficulty of scanning obese women or those who cannot achieve adequate bladder filling for transabdominal US. The technique may be inappropriate for young girls or elderly women with vaginal stenosis. • Explain the technique to the patient (can be likened to a vaginal speculum examination / smear test) and obtain her verbal consent to perform the examination. • Male radiologists should have an escort in the room. Technique: • The patient should empty her bladder immediately prior to the endovaginal scan. • While she is doing so, connect the transducer, and recall the endovaginal scanning set up. • Cover the transducer face with US gel, cover the transducer with a condom secured with tape, exclude air from the end and apply KY gel to the outside. • Cover the patient's thighs with paper and ensure that no-one can come into the room unexpectedly. • Show the patient the transducer. The patient lies supine with her bottom raised on pillows and her knees bent • Ask her to relax while you insert the transducer gently. Manoeuvre the transducer to visualise the organs in the anterior part of the pelvis. ROUTINE EXAMINATION 1. Sagittal and parasagittal views : (Sagittal / oblique relative to uterus) The orientation differs from that of a transabdominal ultrasound scan. In a transabdominal scan, the central ultrasound pulse travels in an antero-posterior direction through the bladder and the cephalic end of the uterus appears on the left of the image. In transvaginal scanning, the incident beam travels in a cephalocaudal direction and the cervix appears at the top of the image, with the corpus of the uterus below it. In a true sagittal scan, the (empty) bladder can be seen on the ventral (anterior) side. • With the transducer tip at the external os of the cervix, sweep through the uterus from side to side in a sagittal plane. Orientate the probe along the long axis of the uterus and examine the endometrium (hyperintense to myometrium). Measure the AP thickness. 2. Trans-pelvic views: (Coronal /oblique relative to uterus) • Orientation : Turn the marker on the transducer head to the patient’s right. The cervix still appears at the top of the image, with the body of the uterus below it. However, now the lateral relations of the uterus come into view instead of the bladder. • Sweep up and down and side to side, examining the uterus. • Relocate the tip of the endovaginal probe in the vaginal fornix and examine the right and left adnexae in AP-pelvic and trans-pelvic planes. OBSTETRIC SCANNING. The following guidelines apply to transabdominal scanning in patients undergoing routine examination during pregnancy. Record the first day of the patient's last menstrual period (LMP), and ask about previous pregnancies. First trimester: • The patient will need to have a full bladder as for gynaecological pelvic US. • Scan the uterus and locate the gestation sac: • Signs of early pregnancy include bulkiness of the uterus, loss of the midline echo, and the presence of a small gestation sac. A gestation sac is not normally visible until 5-6 weeks after the first day of the last menstrual period (LMP). Measure mean sac diameter and state whether the yolk sac is visible to provide an estimate of gestation if no fetus is seen. • Identify fetus : • A fetal pole , and fetal heart motion become visible at 7-8 weeks. • From 8-9 weeks, measure the crown-rump length (head to buttocks) from which gestational age can be estimated. • The head and body becomes distinguishable at about 10 weeks. • The biparietal diameter (BPD) measurement of the fetal cranium is used to assess gestational age from about 12 weeks. • Document the number of embryos seen and if there are twins, determine whether monochorionic or dichorionic. • Record the presence or absence of fetal heart activity • Review the uterus and adnexae for abnormality. Second and third trimester • To measure the BPD , the fetal cranium must be scanned transversely, at right angles to the midline. The measurement should be taken at the widest axis of the cranium, usually at the level of the thalami, below the level of the lateral ventricles. Signs that the correct position has been achieved include: • Visualisation of the thalami (paired triangles / diamond), • Visualisation of the third ventricle (between thalami) or cavum septum pellucidum (parallel anterior parasagittal echoes). • The cranium and cerebral hemispheres should be of equal size and shape on either side of the midline, producing a symmetrical ovoid cross-section. • Measure from the leading edge of the proximal skull echoes to the leading edge of the distal skull echoes, perpendicular to the midline echo. • Use of the BPD for estimation of fetal age is appropriate up to 28 weeks. Head circumference , measured at the same level, is an alternative method which can be used if the head shape is abnormal, for example in breech presentation when the head is frequently dolichocephalic. • If the fetal head cannot be assessed, the femoral length is an alternative method for estimating fetal age. After about 24 weeks, the abdominal circumference can be used to assess fetal growth, and is more sensitive to intrauterine growth retardation than the BPD. [...]... can see the lateral edge of the acetabulum, the labrum and the broad echogenic anterior band of the iliofemoral ligament Note that the front of the femur appears flat from this perspective, as the angle at the femoral neck does not come into the image • In a good subject, you should be able to see all the layers in front of the femoral neck forming the anterior pouch of the joint space • Measure the anteroposterior... emerging into the thigh as the femoral vessels HIPS Detection of effusions of the hip joint Ultrasound is the technique of choice Remember that the iliofemoral ligament forms part of the joint capsule and inserts into the linea aspera on the front of the femoral neck, but the thinner, less echogenic synovial membrane underneath it is reflected back up the femoral neck to attach at the margins of the articular... spiral valve of Heister at the top end Portal tract • With the probe turned sagittally, sweep along the right lobe of the liver till you see part of the portal vein as it runs in from the inferior surface To see the length of the main part of the portal vein within the liver, you rotate the probe anti-clockwise from the sagittal so that the plane of • • • • • insonation points roughly at the right shoulder,... internal organ) Then sweep steadily towards the left until you reach the far edge of the left lobe of the liver This may be as far away as the left mid-clavicular line • Now sweep vertically through the liver Place the probe orientated axially under the right-hand side of the ribs, angle it upwards, and check that you can see the top of the liver Now sweep all the way down to the bottom, including the Riedel’s... ventricle as they pass over it (unless there is absence of the corpus callosum) The fluid-filled viscus separating the two medial walls of the anterior horns of the lateral ventricles above the third ventricle is the cavum septi pellucidi, which is a constant finding for the first few months of life The strip of choroid plexus in each lateral ventricle passes down through the foramen of Monroe into the third... the foramina is where the choroid plexus disappears from the lateral ventricles as you sweep forward Measure the ventricular diameters if there is any question of hydrocephalus These are taken at the level of the foramina of Monroe on a true coronal image They are defined as the greatest horizontal distance from the midline to the tip of the lateral ventricle on each side Just behind the foramina of. .. passing through the middle of it • You now need to tilt the probe one way and then the other to see each side of the brain in turn However, you have to be careful to rock the probe using its own point as a fulcrum, rather than sweeping the point of the probe across the surface, as you will lose the image if the probe head • • • • • • • wanders away from the acoustic window formed by the fontanelle This... winding from the temporal horns round to the foramina of Monroe, and should be symmetrical Check the periventricular area lateral to each lateral ventricle Now turn the probe into the coronal plane and look for the foramina of Monroe connecting the underside of the lateral ventricles to the superomedial corners of the third ventricle Note that the whole of the lateral ventricles lie superior to the third... walls If there is not too much bowel gas, you should be able to follow the CBD carefully down through the head of the pancreas to where it turns towards the medial side of the duodenum If you can see two tubes running inferiorly through the right-hand side of the head of the pancreas, the more posterior one is usually the pancreatico-duodenal artery The hepatic artery lies more medial to the portal... and then tilt it to face medially towards the aorta In most people this works when the probe is touching the skin in the mid-clavicular line With a little practice, you will learn to put the probe straight down on the patient to show the length of the portal vein Follow the portal vein down to its origin at the junction of the splenic and superior mesenteric veins, where there is a slight bulge Of the . The MANCHESTER handbook of ULTRASOUND TECHNIQUES THE MANCHESTER HANDBOOK OF ULTRASOUND TECHNIQUES The most important part of a stethoscope is the. along the right lobe of the liver till you see part of the portal vein as it runs in from the inferior surface. To see the length of the main part of the