Xenon-133 is a radiopharmaceutical principally used when a performing VQ scan. Inhalation of this gas can also be used to assess cerebral blood flow.
photon energy: 81 KeV
physical half-life: 5.27 days
biological half-life: 30 seconds
normal distribution: lungs
<15% of inhaled gas is absorb...
The xiphisternum (also known as the xiphoid process or simply the xiphoid) is the smallest of the three parts of the sternum (manubrium, body or gladiolus and xiphisternum). It arises from the inferior and posterior margin of the sternal body and projects inferiorly. It is a small cartilaginous ...
There is considerable anatomic variation in the shape of the xiphoid of the sternum:
xiphoid ending is classified as single, double, or triple.
xiphoid size varies (e.g. elongated process)
xiphoid morphology (e.g. ventral or dorsal deviation, hook-like, reverse S-shape).
X-linked adrenoleukodystrophy is an inherited metabolic peroxisomal disorder and one of the more common leukodystrophies in both children and adults. It is characterized by a lack of oxidation of very long chain fatty acids (VLCFAs) that results in severe inflammatory demyelination typically of ...
X-linked Opitz G/BBB syndrome (XLOS) is an x-linked disorder with a spectrum of congenital anomalies. Anomalies that may be seen are:
broad nasal bridge
cleft lip and/or palate
The X-marks-the-spot is a sign of complete bowel volvulus and refers to the crossing loops of the bowel at the site of the transition. It has been reported to improve diagnostic confidence in detecting cecal and sigmoid volvulus. This is in contrast to the split-wall sign which indicates partial...
Artifacts can present in a variety of ways including abnormal shadow noted on a radiograph or degraded image quality and have been produced by artificial means from hardware failure, operator error and software (post-processing) artifacts.
There are common and distinct artifacts for film, comp...
X-ray film displays the radiographic image and consists of emulsion (single or double) of silver halide (silver bromide (AgBr) is most common) which when exposed to light, produces a silver ion (Ag+) and an electron. The electrons get attached to the sensitivity specks and attract the silver ion...
X-rays in the diagnostic range interact with matter primarily via two processes, which are fundamental in understanding how an image is formed in a radiographic exam. These process are the
X-rays are produced due to sudden deceleration of fast-moving electrons when they collide and interact with the target anode. In this process of deceleration, more than 99% of the electron energy is converted into heat and less than 1% of energy is converted into x-rays.
X-rays represent a form of electromagnetic radiation. They are produced by the x-ray tube, using the high voltage to accelerate the electrons produced by the cathode. The produced electrons interact with the anode, thus producing x-rays. The x-rays produced include Bremsstrahlung and the charact...
An x-ray tube functions as a specific energy converter, receiving the electrical energy and converting it into two other forms of energy: x-radiation and heat. Heat is considered the undesirable product of this conversion process; therefore x-radiation is created by taking the energy from the el...
The Yasargil classification is one of the two common systems for classifying vein of Galen malformations that is currently in use at the time of writing (mid 2016).
type I: small pure cisternal fistula between the vein of Galen (voG) and either the pericallosal arteries (anteri...
The yellow nail syndrome (YNS) is a rare disorder principally affecting the lymphatic system.
It is characterized by a clinical triad:
nail discolouration: yellow slow-growing dystrophic nails (scleronychia)
exudative pleural effusions (leas...
The yin-yang sign is a radiologic appearance described in solitary fibrous tumor of the dura on MR.
On T2-weighted images, these tumors have two separate solid components, one that is hyperintense and one that is iso- to hypointense relative to brain parenchyma. Histologically, the former repre...
The yin-yang sign, also known as the Pepsi sign, is a radiological sign described in both true and false aneurysms on various imaging modalities.
On Doppler ultrasound, the yin-yang sign indicates bidirectional flow due to the swirling of blood within the true...
Yolk sac is the first anatomical structure identified within the gestational sac. It plays a critical role in embryonal development by providing nutrients, serving as the site of initial hematopoiesis, providing endocrine, metabolic and immunological functions and contributing to the development...
The Young and Burgess classification is a modification of the Tile classification 1. It is the recommended 5 and most widely used classification system for pelvic ring fractures.
It takes into account force type, severity, and direction, as well as injury instability.
Young's modulus is a relationship between elasticity, strain, and stress:
elasticity x (change in length / original length) = (force / area)
put another way, this is
elasticity x (strain) = stress
elasticity = stress / strain
Elasticity is measured in kilopascals (kPa).
Young syndrome shares similar clinical and radiological findings to primary ciliary dyskinesia and cystic fibrosis, however the underlying pathogenesis yet to be fully elucidated. Obstructive azoopsermia at the level of the epididymis is thought to be the cause of infertility. The commonly refer...
The Y sign refers to a common appearance in lumbar epidural lipomatosis where excess fat in the extradural space compresses the dural sac into the shape of the letter "Y".
Yunis Varón syndrome is a rare skeletal dysplasia. It is thought to be autosomal recessive.
severe neurologic impairment
diastasis of sutures
absent thumbs and distal phalanges of fingers
The Zabramski classification of cerebral cavernomas has been proposed as a way of classifying cerebral cavernous malformations, and although not used in clinical practice it is useful in scientific publications that seek to study cavernous malformations.
The classification was proposed in 1994 ...
The Z deformity is one of the musculoskeletal manifestation of rheumatoid arthritis in hand:
radial deviation at the wrist
ulnar deviation of the digits, and often
palmar subluxation of the proximal phalanges
The zebra sign has been termed to describe the finding of layering of blood in amongst the folia of the cerebellum, particularly in the setting of remote cerebellar hemorrhage.1
This type of hemorrhage is characterized by a streaky pattern, like a zebra's stripes, due to blood spreading in the ...
Zebra spleen, also referred to as psychedelic spleen or more correctly inhomogeneous splenic enhancement, refers to the transient heterogeneous parenchymal enhancement of the spleen during the arterial or early portal venous phases of contrast enhancement in CT, MRI, or ultrasound imaging.
Zebra stripes/artifacts appear as alternating bright and dark bands in a MRI image. The term has been used to describe several different kind of artifacts causing some confusion.
Artifacts that have been described as a zebra artifact include the following:
Moire fringes 1,2
The zebra stripe sign occurs where children with osteogenesis imperfecta have been treated with cyclical bisphosphonate therapy, e.g. pamidronate. When the drug is delivered in cycles, dense bone is formed while treatment is being given. This results in dense stripes across the metaphyses of bon...
Zellweger syndrome (ZS), also known as the cerebrohepatorenal syndrome, is a multisystem metabolic abnormality. As the name implies it primarily affects the central nervous system (CNS), liver and kidneys.
The condition typically presents in neonates with poor feeding and/or seiz...
Zenker diverticulum, also known as a pharyngeal pouch, is a posterior outpouching of the hypopharynx, just proximal to the upper esophageal sphincter through a weakness in the muscle layer called the Killian dehiscence.
More than 50% of the affected patients present in 60-80 years...
Zero fill artifact is one of many MRI artifacts and is due to data in the K-space array missing or set to zero during scanning. The abrupt change from signal to no signal results in artifacts in the images showing alternating bands of shading and darkness, often in an oblique direction.
Zero filling interpolation (ZIP) is the substitution of zeroes for unmeasured data points in order to increase the matrix size of the new data prior to Fourier transformation of MR data. This results in pixels smaller than the actual resolution of the image. The zero filling occurs in the periph...
Zimmerman-Laband syndrome is a rare congenital syndrome, characterized primarily by gingival hypertrophy and skeletal abnormalities.
The molecular basis of the syndrome is currently unknown. An autosomal dominant mutation with high mutation rate and rare instances of germinal mosaic...
Zinc (chemical symbol Zn) is a trace element with a key role as a constituent of enzymes, e.g. carbonic anhydrase, and as part of zinc finger proteins, vital for the correct folding of macromolecules, such as DNA. More recently zinc has been found to act as an important cellular messenger 3.
Zinc toxicity (also rarely known as zincalism) is rare as the body is remarkably efficient at excreting excess zinc. Typically oral zinc poisoning manifests primarily as:
acute GI symptoms: vomiting, diarrhea, abdominal pain
secondary copper deficiency
zinc competes with copper for absorption...
Zinner syndrome is a triad of mesonephric (Wolffian) duct anomalies comprising unilateral renal agenesis, ipsilateral seminal vesicle cyst, and ejaculatory duct obstruction 1.
Patients are typically diagnosed during the 3rd or 4th decade of life and often present with per...
In MR imaging, zipper artifact refers to a type of MRI artefact where one or more spurious bands of electronic noise extend perpendicular to the frequency encode direction and is present in all images of a series.
There are various causes for zipper artifacts in images. Most of them are...
Zollinger-Ellison syndrome (ZES) is a clinical syndrome that occurs secondary to a gastrinoma.
Diagnosis of ZES is often delayed by 5-7 years after the onset of symptoms 2.
Gastrinomas are usually multiple and typically located in the duodenum (more common) ...
The zona orbicularis are circular fibers of the hip joint capsule and form a collar around the femoral neck. Though partly blended with the pubofemoral and ischiofemoral ligaments, these fibers are not directly attached to bone.
Z-scores are a way to translate individual data points into terms of a standard deviation.
Z = (X - Xbar) / σ
X: individual data point
Xbar: the arithmetic mean
σ: the standard deviation
The purpose of the Z-score is to allow comparison between values in different normal distributions. Two...
Zuckerkandl tubercles are the projections of normal thyroid tissue from the posterior or posteromedial margin of the thyroid gland that extend posterior to the tracheoesophageal groove. They are present in most patients and occur more commonly on the right and in the longitudinal center 50% of t...
Zuelzer-Wilson syndrome, also known as total colonic aganglionosis, is a subset of Hirschsprung disease, in which the whole colon is aganglionic.
It is uncommon and accounts for 2-13% of cases of Hirschsprung disease 3,7. Compared with Hirschsprung disease which has a marked male ...
The Zurich pituitary score (ZPS) is a quantitative classification of pituitary adenomas based on coronal T1W magnetic resonance imaging with contrast, although the score can also be obtained with computed tomography.
The ZPS is based on the ratio (R) between horizontal tumor diameter over inter...
The zygoma (also known as zygomatic bone or malar bone) is an important facial bone which forms the prominence of the cheek. It is roughly quadrangular in shape.
Zygoma has three surfaces, five borders, and two processes.
anterolateral surface is convex, pierced at its...
The zygomatic arch is formed by the union of the temporal process of the zygomatic bone and the zygomatic process of the temporal bone at the zygomaticotemporal suture.
Le Fort type 3 fracture
zygomaticomaxillary complex fracture
The zygomatic nerve is a main branch of the maxillary division of the trigeminal nerve. It should not be confused with the zygomatic branch of the facial nerve.
The zygomatic nerve divides off the maxillary division just after emerging from the foramen rotundum to enter the ptery...
The zygomaticofacial foramen is a small foramen in the mid lateral surface of the zygomatic bone that transmits the zygomaticofacial nerve (a branch of the zygomatic nerve from the maxillary division of the trigeminal nerve) and zygomaticofacial vessels.
The zygomaticofacial nerve is the smaller of the two branches of the zygomatic nerve, from the maxillary division of the trigeminal nerve. It is sometimes referred to as the malar branch of the zygomatic nerve. It leaves the inferolateral aspect of the extraconal space of the orbit through the z...
Zygomaticomaxillary complex (ZMC) fractures, also known as tripod, tetrapod, quadripod, malar or trimalar fractures, are seen in the setting of traumatic injury to the face. They comprise fractures of the:
inferior orbital rim, and anterior and posterior maxillary sinus walls
The zygomaticomaxillary suture is between the zygomatic process of the maxilla and the maxillary process of the zygomatic bone. They are often involved in zygomaticomaxillary complex (ZMC) fractures.
The zygomaticotemporal foramen is a small foramen in the anteromediall surface of the zygomatic bone that transmits the zygomaticotemporal nerve (a branch of the zygomatic nerve from the maxillary division of the trigeminal nerve) and zygomaticotemporal vessels.
The zygomaticotemporal nerve is the larger of the two branches of the zygomatic nerve, from the maxillary division of the trigeminal nerve. It is primarily sensory but also relays parasympathetic fibers to the lacrimal nerve from the pterygopalatine ganglion which reach the lacrimal gland. It le...
Zygomaticus major is a member of the buccolabial muscle group of the upper lip1. It joins with the fibers of levator anguli oris, orbicularis oris and the more deeply placed muscular bands to move the side of the mouth upwards and sideways during facial movements such as laughing.
Zygomaticus minor is a member of the buccolabial muscle group. Together with levator labii superioris alaeque nasi and levator labii superioris it is one of the main elevators of the lip, exposing the maxillary teeth 1. Along with its other action of deepening and elevating the nasolabial furro...