A CT scan uses X-rays to produce images, unlike an MRI scan which uses magnetic fields and radio waves. CT perfusion in ischemic stroke has become established in most centers with stroke services as an important adjunct, along with CT angiography (CTA), to conventional unenhanced CT brain imaging. Brain scans also can identify changes in the brain's structure and function that suggest Alzheimer's disease. This is possible as different tissues interact with X-rays in different ways. “Comparison of gray values of cone-beam computed tomography with Hounsfield units of multislice computed tomography: An in vitro study”. A CT image is produced by firing x-rays at a moving object which is then detected by an array of rotating detectors (Figure 1). Communicating hydrocephalus is first evident in dilation of the temporal horns (normally small, slit-like). This article will cover some of the underlying principles of CT head studies, and discuss a method for their interpretation. This builds upon our first article titled "How to interpret an unenhanced CT Brain scan. Licence: [, Aaron G. Filler, MD, PhD, FRCS. Look for abnormal shifts of brain tissue and/or herniation: Hypodensity on a CT head may be due to the presence of air, oedema or fat: Hyperdensity on a CT head may be due to the presence of blood, thrombus or calcification: The radiological features of a tumour will vary depending on the histological diagnosis. Brain CT scans can provide more detailed information about brain tissue and brain structures than standard X-rays of the head… Licence: [. The patient had no recollection of the event (Figures 1-2). A subdural haematoma forms between the dura and the arachnoid mater and typically develops secondary to trauma (as a result of tearing of bridging veins). Cerebral metastases. This problem is negotiated with windowing. Cover the basics of Computed Tomography (CT) Brain imaging. CT Head: Extremely important investigation • CT head is an extremely important investigation used routinely in indoor as well as ER patients. 8. Pneumocephalus. Journal of Digital Imaging 2007;20(4):422-432. The anterior part of the head is at the top of the image. Subscribe to the Health Matters newsletter today. The images produced by a CT scan provide detailed information about brain tissue and brain … The aim of this article is to: 1. Hypoxic brain injury. • To prevent unnecessary irradiation of the orbits, Head CTs are performed at an angle parallel to the base of the skull. Computed tomography (CT) is an imaging technique that employs a rotating x-ray generator and multiple detectors to produce a large number of cross-sectional images on several planes. The majority of cases of extradural haematoma result from trauma to the middle meningeal artery. I think this played a big part in the decision-making of the ER … Subtle areas of low density within the inner table of the skull may represent small locules of air in the soft tissue windows. Some tissues will allow the passage of X-rays without influencing them much, whilst other tissues will exert a more significant effect. Content and images below are taken from his lecture (with his permission). Basic categories of blood in the brain are epidural, subdural, intraparenchymal/intracerebral, intraventricular, and subarachnoid. On a normal CT head scan, the grey and white matter should be clearly differentiated. Look for fractures of the calvarium and skull base. What is a CT scan of the brain? Licence: [, James Heilman, MD. This means that the right side of the brain is on the left side of the viewer. CT scan machine 3. Once the anatomy is known, a systematic review of the images should be performed so as not to miss any abnormal structure… Pathologic processes cause dilation (hydrocephalus) or compression/shift. Each clinical case scenario allows you to work through history taking, investigations, diagnosis and management. How to read a head CT scan. Assess the bones of the skull using the appropriate windowing. SHL 2. In elderly patients who have experienced a fall, the inciting traumatic event may be less obvious. Why am I having a brain CT scan? Head CT technique, normal anatomy and common pathology are presented. Epidural (lens shaped, does not cross suture lines), Subdural (crescent shaped, does cross suture lines), Intraparenchymal /intracerbral hemorrhage (high density bleeds most often in the basal ganglia area if due to HTN), Subarachnoid hemorrhage (due most often to aneurysms, CT sensitivity decreases sharply with time), Two key questions to answer regarding the four key cisterns (Circummesencephalic, Suprasellar, Quadrigeminal and Sylvian). (easiest when patient not rotated in the scanner) Grey-white differentiation - the earliest sign of a CVA on CT scan is the loss of the grey-white interface on CT scan. Before starting this tutorial please read the CT brain … Subdural haemorrhage. open in new tab, Events & Classes The most common types of brain scans are computed tomographic (CT) scans and magnetic resonance imaging (MRI). Windowing (also known as grey-level mapping) is the process of changing the location and width of the available greyscale in order to optimise discrimination between tissues. In short, there will not be enough contrast to reliably discern between structures. A hyperdense middle cerebral artery (MCA) is sometimes noted in total anterior circulation strokes (TACS) and indicates the presence of a large thrombus within the vessel. This may result from cerebral oedema secondary to a mass or an intracranial haemorrhage. Suprasellar cistern: superior to the sella turcica. A collection of anatomy notes covering the key anatomy concepts that medical students need to learn. 3. The meninges are composed of three layers: pia mater (that is in direct contact with grey matter and contains supplying capillaries), arachnoid network (that contains CS… A CT scan is usually one of the first tests done in a stroke evaluation, particularly during an acute stroke in the emergency room. Remember a SAH can extend into the ventricular system so always look at the posterior horns as blood may collect in the dependant portion. A collection of interactive medical and surgical clinical case scenarios to put your diagnostic and management skills to the test. Licence: [, James Heilman, MD. A comprehensive collection of clinical examination OSCE guides that include step-by-step images of key steps, video demonstrations and PDF mark schemes. Fine X-ray beams passed through the subject are absorbed to different degrees by different tissues and the transmitted radiation is measured by … This web site is intended as a self-tutorial for residents and medical students to learn to interpret head CT scans with confidence. Below we can see a greyscale (from white to black) being assigned to the whole range of HU (from air to cortical bone). It is more efficient when an immediate diagnosis is required such as intracranial bleeds, dissection of a blood vessel, or renal stones. Blood Can Be Very Bad is a mnemonic that can be used when faced with interpreting a CT head scan: Think of this approach as a framework for a quick review of a scan – it won’t turn you into an experienced radiologist! Examine the brain for: Symmetry - make sure sulci and gyri appear the same on both sides. Some bleeds may also be very subtle and difficult to spot unless you look closely and this is one of the reasons why windowing is so important. The lateral, IIIrd, and IVth ventricles need to be examined for effacement, shift, and blood. The cranium, enclosing the brain, forms a fixed space comprising three components: blood, cerebrospinal fluid, and brain tissue. Compare side to side. NYP Professionals Emergency Medicine Education How to read a head CT, NYP Professionals Emergency Medicine Education, NYP Professionals Emergency Medicine Education How to Read Emergency Images. Ambient cistern: surrounding the midbrain. Case 1. These values are frequently expressed as Hounsfield units (HU). obstructive). A new kind of brain scan, called a DaT scan, does show changes in persons with Parkinsons disease and may someday become an important tool in diagnosing Parkinsons. It can be broadly divided into communicating (i.e. Benefits of the Scan. Still, CTP interpretation … This is possible as different tissues interact with X-rays in different ways. The mnemonic used by Dr. Andrew Perron who lectures on this topic frequently is: "Blood Can Be Very Bad". A collection of free medical student quizzes to put your medical and surgical knowledge to the test! CT scans have an advantage over x-rays however because the large amount of data a CT scan provides, allows doctors to be able to manipulate the data into different views … You achieve the best contrast in an image has 0 HU, whereas air the! Can rise rapidly and without prompt evacuation of the temporal horns who interprets the in! 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