Basic principles of imaging methods

Basic principles of imaging methods

Conventional radiography Although it is over 120 years since the discovery of x-rays by - Roentgen in 1895, conventional radiography continues to play a central role in the diagnostic pathway of many acute orthopaedics. X-rays emitted from an x-ray source are absorbed to vary ing degrees by di ff erent materials and tissues and therefore cause di ff erent degrees of blackening of radiographic film, resulting in a radiographic image. This di ff er ential absorption is dependent partly on the density and the atomic number of di ff erent substances. In general, higher density tissues result in a greater reduction in the number of x-ray photons and reduce the amount of blackening caused by those photons. In terms of conventional radiographs, a large di ff erence in tissue structure and density is required before an appreciable di ff erence is man ifested radiographically . The di ff erent densities visible consist of air, fat, soft tissue, bone and mineralisation, and metal. Dif ferent soft tissues cannot be reliably distinguished as, in broad terms, they possess similar quantities of water ( Figur e 8.1 Manipulation of x-ray systems and x-ray energies, as used in circumstances such as mammography , may allow better dif fer entiation between some soft-tissue structures. Despite this inherent lack of soft-tissue contrast, conventional radiography has many advantages. It is cheap, universally available , easily reproducible and comparable with prior examinations and, in many instances, has a relatively low dose of ionising radiation in contrast to more complex examinations. However, injudi cious repeat radiography , particularly of the abdomen, pelvis and spine, can easily result in doses similar to CT . The lack of soft-tissue contrast allows little assessment of the internal architecture of many abdominal organs. To ob ate this problem, techniques emplo ying the administration of contrast material combined with radiography have long been used. These techniques include intravenous urography (IVU) and barium examinations ( Figur e 8.2 ) . IVU involves a series of radiographs taken before and after contrast injection, but has been largely superseded by CT urog raphy , which is more accurate in detecting and defining pathology ( Figure 8.3 further modification of conventional x-rays uses fluorescent screens to allow real-time monitoring of organs and structures as opposed to the ‘snapshot’ images obtained with radiographs. This is used to follow the passage of barium through the bowel, obtaining dedicated images at specific points of interest only . Motility of the bowel can also be assessed in this way . Fluoros copy is used extensively in interventional radiology , allowing the operator to guide catheters and wires into the patient while monitoring their position in real time. Naturally , with the more sustained use of ionising radia tion, the cumulative doses tend to be greater than when obtain ing a conventional radiograph. Ultrasound Ultrasound is the second most commonly used method of imaging. It relies on high-frequency sound waves generated by a transducer containing piezoelectric material. The generated sound waves are reflected by tissue interfaces and, by ascertain ing the time taken for a pulse to return and the magnitude and direction of a pulse, it is possible to form an image. Medical ultrasound uses frequencies in the range 3–20 /uni00A0 MHz. The higher the frequency of the ultrasound wave, the gr eater the resolution of the image, but the less depth of view from the skin. Consequently , abdominal imaging uses transducers with - - - ) . - - vi - ) . A - - - -

Figure 8.1 Supine abdominal radiograph of a patient with small bowel obstruction demonstrates multiple dilated small bowel loops. The different densities visible are air (within the bowel), bones, soft tissues and fat. The different soft tissues, subcutaneous and intra-abdominal, cannot be differentiated. Figure 8.2 Barium swallow examination showing a malignant stricture (arrow) due to an oesophageal carcinoma.

a frequency of 3–7 /uni00A0 MHz, while higher frequency transducers are used for superficial structures, such as musculoskeletal and breast ultrasound. Dedicated transducers have also been developed for endocavity ultrasound, such as transvaginal scanning and transrectal ultrasound of the prostate, allowing high-frequency scanning of organs by reducing the distance between the probe and the organ of interest ( Figure 8.4 further application of dedicated probes has been in the field of endoscopic ultrasound, allowing exquisite imaging of the wall of a hollow viscus and the adjacent organs such as the biliary tree and pancreas. Reflection of an ultrasound wave from moving objects such as red blood cells causes a change in the frequency of the ultrasound wave. By measuring this frequency change, it is ). A possible to calculate the speed and direction of the movement. This principle forms the basis of Doppler ultrasound, whereby velocities within major vessels, as well as smaller vessels in organs such as the liver and the kidneys, can be measured.

Figure 8.3 Coronal maximum intensity projection image from a computed tomography intravenous urogram shows a transitional cell carcinoma in the left renal pelvis (arrow) with normal excretion of contrast on the right. Figure 8.4 Longitudinal transvaginal ultrasound scan of the uterus demonstrates thickening of the endometrium in a patient during the secretory phase of the menstrual cycle. Figure 8.5 Transverse ultrasound image of the liver in a patient with colorectal cancer shows a solitary liver metastasis. (a) (b) Figure 8.6 Sagittal ultrasound image of the liver (a) in a patient with cirrhosis demonstrates nodularity of the liver surface and extensive ascites. Doppler ultrasound (b) illustrates portal vein /f_l ow with a normal direction.

and venous disease, in which stenotic lesions cause an alter ation in the normal velocity . Furthermore, di ff use parenchymal diseases, such as cirrhosis, may cause an alteration in the nor mal Doppler signal of the blood vessels of the a ff ected organ. The advantages of ultrasound are that it is cheap and easily available. It is the first-line investigation of choice for assessment of the liver, the biliary tr ee and the renal tract ( Figures 8.5 and 8.6 ) . Ultrasound is also the imaging method of choice in obstetric assessment and gynaecological disease. High-frequency transducers have made ultrasound the best imaging technique for the evaluation of thyroid and testicular disorders, in terms of both di ff use disease and focal mass lesions. It is also an invaluable tool for guiding needle placement in interventional procedures such as biopsies and drainages, allowing direct real-time visualisation of the needle during the procedure. Ligament, tendon and muscle injuries are also probably best imaged in the first instance by ultrasound ( Figure 8.7 ). The ability to stress ligaments and to allow tendons to move during the investigation gives an extra dimension, which greatly improves its diagnostic value. T he use of ‘panoramic’ or ‘extended field of view’ ultrasound ( Figure 8.8 ) provides images that are more easily interpreted by an observer not performing the examination, and are of particular assistance to surgeons planning a procedure. Ultrasound will demonstrate most foreign bodies in soft tissues, including those tha t are not radio-opaque. tor dependent, and most of the information is obtained during - the actual process of scanning as opposed to reviewing the static images. Another drawback is that the ultrasound wave - is highly attenuated by air and bone and, thus, little infor ma - tion is gained with regard to tissues beyond bony or air-filled structures; alternative techniques may be required to image these areas. Summary box 8.4 Ultrasound /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

Figure 8.7 Ultrasound of the dorsal surface of the wrist shows the normal /f_i brillar pattern of the extensor tendons. There is increased /f_l uid (arrow) within the tendon sheath in this patient with extensor tenosynovitis. Figure 8.8 Panoramic ultrasound of the calf. The normal muscle /f_i bres and the fascia can be identi /f_i ed over an area measuring approximately 12 cm. Strengths No radiation Inexpensive Allows interaction with patients Superb soft-tissue resolution in the near /f_i eld Dynamic studies can be performed First-line investigation for hepatic, biliary and renal disease Endocavity ultrasound for gynaecological and prostate disorders Excellent resolution for breast, thyroid and testis imaging Good for soft tissue, including tendons and ligaments Excellent for cysts and foreign bodies Doppler studies allow assessment of blood /f_l ow Good real-time imaging to guide interventional biopsies and drainages Weaknesses Interpretation only possible during the examination Visualisation of structures can be hampered by overlying gas and bone, and body habitus may also impact on the scan Long learning curve for some areas of expertise Resolution dependent on the machine available Images cannot be reliably reviewed away from the patient

Basic principles of imaging methods

Conventional radiography Although it is over 120 years since the discovery of x-rays by - Roentgen in 1895, conventional radiography continues to play a central role in the diagnostic pathway of many acute orthopaedics. X-rays emitted from an x-ray source are absorbed to vary ing degrees by di ff erent materials and tissues and therefore cause di ff erent degrees of blackening of radiographic film, resulting in a radiographic image. This di ff er ential absorption is dependent partly on the density and the atomic number of di ff erent substances. In general, higher density tissues result in a greater reduction in the number of x-ray photons and reduce the amount of blackening caused by those photons. In terms of conventional radiographs, a large di ff erence in tissue structure and density is required before an appreciable di ff erence is man ifested radiographically . The di ff erent densities visible consist of air, fat, soft tissue, bone and mineralisation, and metal. Dif ferent soft tissues cannot be reliably distinguished as, in broad terms, they possess similar quantities of water ( Figur e 8.1 Manipulation of x-ray systems and x-ray energies, as used in circumstances such as mammography , may allow better dif fer entiation between some soft-tissue structures. Despite this inherent lack of soft-tissue contrast, conventional radiography has many advantages. It is cheap, universally available , easily reproducible and comparable with prior examinations and, in many instances, has a relatively low dose of ionising radiation in contrast to more complex examinations. However, injudi cious repeat radiography , particularly of the abdomen, pelvis and spine, can easily result in doses similar to CT . The lack of soft-tissue contrast allows little assessment of the internal architecture of many abdominal organs. To ob ate this problem, techniques emplo ying the administration of contrast material combined with radiography have long been used. These techniques include intravenous urography (IVU) and barium examinations ( Figur e 8.2 ) . IVU involves a series of radiographs taken before and after contrast injection, but has been largely superseded by CT urog raphy , which is more accurate in detecting and defining pathology ( Figure 8.3 further modification of conventional x-rays uses fluorescent screens to allow real-time monitoring of organs and structures as opposed to the ‘snapshot’ images obtained with radiographs. This is used to follow the passage of barium through the bowel, obtaining dedicated images at specific points of interest only . Motility of the bowel can also be assessed in this way . Fluoros copy is used extensively in interventional radiology , allowing the operator to guide catheters and wires into the patient while monitoring their position in real time. Naturally , with the more sustained use of ionising radia tion, the cumulative doses tend to be greater than when obtain ing a conventional radiograph. Ultrasound Ultrasound is the second most commonly used method of imaging. It relies on high-frequency sound waves generated by a transducer containing piezoelectric material. The generated sound waves are reflected by tissue interfaces and, by ascertain ing the time taken for a pulse to return and the magnitude and direction of a pulse, it is possible to form an image. Medical ultrasound uses frequencies in the range 3–20 /uni00A0 MHz. The higher the frequency of the ultrasound wave, the gr eater the resolution of the image, but the less depth of view from the skin. Consequently , abdominal imaging uses transducers with - - - ) . - - vi - ) . A - - - -

Figure 8.1 Supine abdominal radiograph of a patient with small bowel obstruction demonstrates multiple dilated small bowel loops. The different densities visible are air (within the bowel), bones, soft tissues and fat. The different soft tissues, subcutaneous and intra-abdominal, cannot be differentiated. Figure 8.2 Barium swallow examination showing a malignant stricture (arrow) due to an oesophageal carcinoma.

a frequency of 3–7 /uni00A0 MHz, while higher frequency transducers are used for superficial structures, such as musculoskeletal and breast ultrasound. Dedicated transducers have also been developed for endocavity ultrasound, such as transvaginal scanning and transrectal ultrasound of the prostate, allowing high-frequency scanning of organs by reducing the distance between the probe and the organ of interest ( Figure 8.4 further application of dedicated probes has been in the field of endoscopic ultrasound, allowing exquisite imaging of the wall of a hollow viscus and the adjacent organs such as the biliary tree and pancreas. Reflection of an ultrasound wave from moving objects such as red blood cells causes a change in the frequency of the ultrasound wave. By measuring this frequency change, it is ). A possible to calculate the speed and direction of the movement. This principle forms the basis of Doppler ultrasound, whereby velocities within major vessels, as well as smaller vessels in organs such as the liver and the kidneys, can be measured.

Figure 8.3 Coronal maximum intensity projection image from a computed tomography intravenous urogram shows a transitional cell carcinoma in the left renal pelvis (arrow) with normal excretion of contrast on the right. Figure 8.4 Longitudinal transvaginal ultrasound scan of the uterus demonstrates thickening of the endometrium in a patient during the secretory phase of the menstrual cycle. Figure 8.5 Transverse ultrasound image of the liver in a patient with colorectal cancer shows a solitary liver metastasis. (a) (b) Figure 8.6 Sagittal ultrasound image of the liver (a) in a patient with cirrhosis demonstrates nodularity of the liver surface and extensive ascites. Doppler ultrasound (b) illustrates portal vein /f_l ow with a normal direction.

and venous disease, in which stenotic lesions cause an alter ation in the normal velocity . Furthermore, di ff use parenchymal diseases, such as cirrhosis, may cause an alteration in the nor mal Doppler signal of the blood vessels of the a ff ected organ. The advantages of ultrasound are that it is cheap and easily available. It is the first-line investigation of choice for assessment of the liver, the biliary tr ee and the renal tract ( Figures 8.5 and 8.6 ) . Ultrasound is also the imaging method of choice in obstetric assessment and gynaecological disease. High-frequency transducers have made ultrasound the best imaging technique for the evaluation of thyroid and testicular disorders, in terms of both di ff use disease and focal mass lesions. It is also an invaluable tool for guiding needle placement in interventional procedures such as biopsies and drainages, allowing direct real-time visualisation of the needle during the procedure. Ligament, tendon and muscle injuries are also probably best imaged in the first instance by ultrasound ( Figure 8.7 ). The ability to stress ligaments and to allow tendons to move during the investigation gives an extra dimension, which greatly improves its diagnostic value. T he use of ‘panoramic’ or ‘extended field of view’ ultrasound ( Figure 8.8 ) provides images that are more easily interpreted by an observer not performing the examination, and are of particular assistance to surgeons planning a procedure. Ultrasound will demonstrate most foreign bodies in soft tissues, including those tha t are not radio-opaque. tor dependent, and most of the information is obtained during - the actual process of scanning as opposed to reviewing the static images. Another drawback is that the ultrasound wave - is highly attenuated by air and bone and, thus, little infor ma - tion is gained with regard to tissues beyond bony or air-filled structures; alternative techniques may be required to image these areas. Summary box 8.4 Ultrasound /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

Figure 8.7 Ultrasound of the dorsal surface of the wrist shows the normal /f_i brillar pattern of the extensor tendons. There is increased /f_l uid (arrow) within the tendon sheath in this patient with extensor tenosynovitis. Figure 8.8 Panoramic ultrasound of the calf. The normal muscle /f_i bres and the fascia can be identi /f_i ed over an area measuring approximately 12 cm. Strengths No radiation Inexpensive Allows interaction with patients Superb soft-tissue resolution in the near /f_i eld Dynamic studies can be performed First-line investigation for hepatic, biliary and renal disease Endocavity ultrasound for gynaecological and prostate disorders Excellent resolution for breast, thyroid and testis imaging Good for soft tissue, including tendons and ligaments Excellent for cysts and foreign bodies Doppler studies allow assessment of blood /f_l ow Good real-time imaging to guide interventional biopsies and drainages Weaknesses Interpretation only possible during the examination Visualisation of structures can be hampered by overlying gas and bone, and body habitus may also impact on the scan Long learning curve for some areas of expertise Resolution dependent on the machine available Images cannot be reliably reviewed away from the patient

Basic principles of imaging methods

Conventional radiography Although it is over 120 years since the discovery of x-rays by - Roentgen in 1895, conventional radiography continues to play a central role in the diagnostic pathway of many acute orthopaedics. X-rays emitted from an x-ray source are absorbed to vary ing degrees by di ff erent materials and tissues and therefore cause di ff erent degrees of blackening of radiographic film, resulting in a radiographic image. This di ff er ential absorption is dependent partly on the density and the atomic number of di ff erent substances. In general, higher density tissues result in a greater reduction in the number of x-ray photons and reduce the amount of blackening caused by those photons. In terms of conventional radiographs, a large di ff erence in tissue structure and density is required before an appreciable di ff erence is man ifested radiographically . The di ff erent densities visible consist of air, fat, soft tissue, bone and mineralisation, and metal. Dif ferent soft tissues cannot be reliably distinguished as, in broad terms, they possess similar quantities of water ( Figur e 8.1 Manipulation of x-ray systems and x-ray energies, as used in circumstances such as mammography , may allow better dif fer entiation between some soft-tissue structures. Despite this inherent lack of soft-tissue contrast, conventional radiography has many advantages. It is cheap, universally available , easily reproducible and comparable with prior examinations and, in many instances, has a relatively low dose of ionising radiation in contrast to more complex examinations. However, injudi cious repeat radiography , particularly of the abdomen, pelvis and spine, can easily result in doses similar to CT . The lack of soft-tissue contrast allows little assessment of the internal architecture of many abdominal organs. To ob ate this problem, techniques emplo ying the administration of contrast material combined with radiography have long been used. These techniques include intravenous urography (IVU) and barium examinations ( Figur e 8.2 ) . IVU involves a series of radiographs taken before and after contrast injection, but has been largely superseded by CT urog raphy , which is more accurate in detecting and defining pathology ( Figure 8.3 further modification of conventional x-rays uses fluorescent screens to allow real-time monitoring of organs and structures as opposed to the ‘snapshot’ images obtained with radiographs. This is used to follow the passage of barium through the bowel, obtaining dedicated images at specific points of interest only . Motility of the bowel can also be assessed in this way . Fluoros copy is used extensively in interventional radiology , allowing the operator to guide catheters and wires into the patient while monitoring their position in real time. Naturally , with the more sustained use of ionising radia tion, the cumulative doses tend to be greater than when obtain ing a conventional radiograph. Ultrasound Ultrasound is the second most commonly used method of imaging. It relies on high-frequency sound waves generated by a transducer containing piezoelectric material. The generated sound waves are reflected by tissue interfaces and, by ascertain ing the time taken for a pulse to return and the magnitude and direction of a pulse, it is possible to form an image. Medical ultrasound uses frequencies in the range 3–20 /uni00A0 MHz. The higher the frequency of the ultrasound wave, the gr eater the resolution of the image, but the less depth of view from the skin. Consequently , abdominal imaging uses transducers with - - - ) . - - vi - ) . A - - - -

Figure 8.1 Supine abdominal radiograph of a patient with small bowel obstruction demonstrates multiple dilated small bowel loops. The different densities visible are air (within the bowel), bones, soft tissues and fat. The different soft tissues, subcutaneous and intra-abdominal, cannot be differentiated. Figure 8.2 Barium swallow examination showing a malignant stricture (arrow) due to an oesophageal carcinoma.

a frequency of 3–7 /uni00A0 MHz, while higher frequency transducers are used for superficial structures, such as musculoskeletal and breast ultrasound. Dedicated transducers have also been developed for endocavity ultrasound, such as transvaginal scanning and transrectal ultrasound of the prostate, allowing high-frequency scanning of organs by reducing the distance between the probe and the organ of interest ( Figure 8.4 further application of dedicated probes has been in the field of endoscopic ultrasound, allowing exquisite imaging of the wall of a hollow viscus and the adjacent organs such as the biliary tree and pancreas. Reflection of an ultrasound wave from moving objects such as red blood cells causes a change in the frequency of the ultrasound wave. By measuring this frequency change, it is ). A possible to calculate the speed and direction of the movement. This principle forms the basis of Doppler ultrasound, whereby velocities within major vessels, as well as smaller vessels in organs such as the liver and the kidneys, can be measured.

Figure 8.3 Coronal maximum intensity projection image from a computed tomography intravenous urogram shows a transitional cell carcinoma in the left renal pelvis (arrow) with normal excretion of contrast on the right. Figure 8.4 Longitudinal transvaginal ultrasound scan of the uterus demonstrates thickening of the endometrium in a patient during the secretory phase of the menstrual cycle. Figure 8.5 Transverse ultrasound image of the liver in a patient with colorectal cancer shows a solitary liver metastasis. (a) (b) Figure 8.6 Sagittal ultrasound image of the liver (a) in a patient with cirrhosis demonstrates nodularity of the liver surface and extensive ascites. Doppler ultrasound (b) illustrates portal vein /f_l ow with a normal direction.

and venous disease, in which stenotic lesions cause an alter ation in the normal velocity . Furthermore, di ff use parenchymal diseases, such as cirrhosis, may cause an alteration in the nor mal Doppler signal of the blood vessels of the a ff ected organ. The advantages of ultrasound are that it is cheap and easily available. It is the first-line investigation of choice for assessment of the liver, the biliary tr ee and the renal tract ( Figures 8.5 and 8.6 ) . Ultrasound is also the imaging method of choice in obstetric assessment and gynaecological disease. High-frequency transducers have made ultrasound the best imaging technique for the evaluation of thyroid and testicular disorders, in terms of both di ff use disease and focal mass lesions. It is also an invaluable tool for guiding needle placement in interventional procedures such as biopsies and drainages, allowing direct real-time visualisation of the needle during the procedure. Ligament, tendon and muscle injuries are also probably best imaged in the first instance by ultrasound ( Figure 8.7 ). The ability to stress ligaments and to allow tendons to move during the investigation gives an extra dimension, which greatly improves its diagnostic value. T he use of ‘panoramic’ or ‘extended field of view’ ultrasound ( Figure 8.8 ) provides images that are more easily interpreted by an observer not performing the examination, and are of particular assistance to surgeons planning a procedure. Ultrasound will demonstrate most foreign bodies in soft tissues, including those tha t are not radio-opaque. tor dependent, and most of the information is obtained during - the actual process of scanning as opposed to reviewing the static images. Another drawback is that the ultrasound wave - is highly attenuated by air and bone and, thus, little infor ma - tion is gained with regard to tissues beyond bony or air-filled structures; alternative techniques may be required to image these areas. Summary box 8.4 Ultrasound /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

Figure 8.7 Ultrasound of the dorsal surface of the wrist shows the normal /f_i brillar pattern of the extensor tendons. There is increased /f_l uid (arrow) within the tendon sheath in this patient with extensor tenosynovitis. Figure 8.8 Panoramic ultrasound of the calf. The normal muscle /f_i bres and the fascia can be identi /f_i ed over an area measuring approximately 12 cm. Strengths No radiation Inexpensive Allows interaction with patients Superb soft-tissue resolution in the near /f_i eld Dynamic studies can be performed First-line investigation for hepatic, biliary and renal disease Endocavity ultrasound for gynaecological and prostate disorders Excellent resolution for breast, thyroid and testis imaging Good for soft tissue, including tendons and ligaments Excellent for cysts and foreign bodies Doppler studies allow assessment of blood /f_l ow Good real-time imaging to guide interventional biopsies and drainages Weaknesses Interpretation only possible during the examination Visualisation of structures can be hampered by overlying gas and bone, and body habitus may also impact on the scan Long learning curve for some areas of expertise Resolution dependent on the machine available Images cannot be reliably reviewed away from the patient