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What is city scan: CT scan – Mayo Clinic

Computed Tomography (CT) Scan | Johns Hopkins Medicine

What You Need to Know

  • A CT scan is a diagnostic imaging exam that uses X-ray technology to produce images of the inside of the body.
  • A CT scan can show detailed images of any part of the body, including the bones, muscles, organs and blood vessels.
  • CT scans can also be used for fluid or tissue biopsies, or as part of preparation for surgery or treatment.
  • CT scans are frequently done with and without contrast agent to improve the radiologist’s ability to find any abnormalities.

What is a CT scan?

Computed tomography is commonly referred to as a CT scan. A CT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body. It shows detailed images of any part of the body, including the bones, muscles, fat, organs and blood vessels.

CT scans are more detailed than standard X-rays. In standard X-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle and other tissue. While much information can be obtained from a regular X-ray, a lot of detail about internal organs and other structures is not available.

In CT, the X-ray beam moves in a circle around the body. This allows many different views of the same organ or structure and provides much greater detail. The X-ray information is sent to a computer that interprets the X-ray data and displays it in two-dimensional form on a monitor. Newer technology and computer software makes three-dimensional images possible.

CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. CT can also be used for a tissue or fluid biopsy.

Why are CT scans sometimes ordered with contrast?

CT scans may be done with or without contrast. Contrast refers to a substance taken by mouth or injected into an IV line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure. Your doctor will notify you of this prior to the procedure.

You will need to let your doctor know if you have ever had a reaction to any contrast media and/or any kidney problems. A reported seafood allergy is not considered to be a contraindication for iodinated contrast. If you have any medical conditions or recent illnesses, inform your doctor.

How do I prepare for a CT scan?

If you are having a computed tomography angiography (CTA) or a virtual colonoscopy, you will be given specific instructions when you make your appointment.

PRECAUTIONS: If you are pregnant or think you may be pregnant, please check with your doctor before scheduling the exam.

CLOTHING: You may be asked to change into a patient gown. If so, a gown will be provided for you. Please remove all piercings and leave all jewelry and valuables at home.

CONTRAST MEDIA: Contrast may be indicated for your exam. The contrast media improves the radiologist’s ability to find structures that are abnormal and understand normal anatomy better.

  • Some patients should not have an iodine-based contrast media. If you have problems with your kidney function, please inform your radiologist in advance. We may be able to perform the scan without the contrast media or find an alternate imaging exam.
  • The most common type of CT scan with contrast is the double-contrast study, which will require you to drink a contrast media before your exam begins in addition to the IV contrast. The more contrast you are able to drink, the better the images are for the radiologist to visualize your digestive tract.

ALLERGY: Please inform the access center representative when you schedule your scan if you have had an allergic reaction to any contrast media. IV contrast will not be administered if you have had a severe or anaphylactic reaction to any contrast media in the past. Mild to moderate reactions warrant a plan that includes taking medication prior to the CT examination. These plans will be discussed with you in detail when you schedule your exam. Any known reactions to a contrast media should be discussed with your personal physician.

EAT/DRINK: If your study was ordered without contrast, you can eat, drink and take your prescribed medications prior to your exam.

If your doctor orders a CT scan with contrast, do not eat anything three hours prior to your CT scan. We encourage you to drink clear liquids. You may also take your prescribed medications prior to your exam.

DIABETICS: People with diabetes should eat a light breakfast or lunch three hours prior to the scan time. Depending on your oral medication for diabetes, you may be asked to discontinue use of the medication for 48 hours after the CT examination. Detailed instructions will be given following your examination.

MEDICATION: All patients can take their prescribed medications as usual.

The Newest CT: Faster Than a Heartbeat

A new CT scanner will change the management and outcomes of coronary artery disease. The CT scan captures images of the heart between beats, leading to clearer images to help detect anatomic and functional characteristics of coronary artery disease. This technology can also be used to help replace invasive tests to determine which patients with chest pain need intervention.

Read more

What are the risks of a CT scan?

If you are pregnant or think you may be pregnant, you should notify your health care provider.

The amount of radiation dose used in a CT scan is small. You may want to ask your doctor about the amount of radiation used during the CT procedure and the risks related to your particular situation.

If you are claustrophobic or tend to become anxious easily, tell your doctor ahead of time. You may be prescribed a mild sedative to take before the procedure to make you more comfortable.

What happens during a CT scan?

CT scans may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician’s practices. Generally, CT scans follow this process:

  • You may be asked to change into a patient gown. If so, a gown will be provided for you. A locker will be provided to secure all personal belongings. Please remove all piercings and leave all jewelry and valuables at home.
  • If you are to have a procedure done with contrast, an IV line will be started in the hand or arm for injection of the contrast media. For oral contrast, you will be given a liquid contrast preparation to swallow. In some situations, the contrast may be given rectally.
  • You will lie on a scan table that slides into a large, circular opening of the scanning machine.
  • The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window. Speakers inside the scanner will enable the technologist to communicate with and hear you. You may have a call button so that you can let the technologist know if you have any problems during the procedure. The technologist will be watching you at all times and will be in constant communication.
  • As the scanner begins to rotate around you, X-rays will pass through the body for short amounts of time. You will hear clicking sounds, which are normal.
  • The X-rays absorbed by the body’s tissues will be detected by the scanner and transmitted to the computer. The computer will transform the information into an image to be interpreted by the radiologist.
  • It is important that you remain very still during the procedure. You may be asked to hold your breath at various times during the procedure.
  • If contrast media is used for your procedure, you may feel some effects when the contrast is injected into the IV line. These effects include a flushing sensation, a salty or metallic taste in the mouth, a brief headache, or nausea and/or vomiting. These effects usually last for a few moments.
  • You should notify the technologist if you have any breathing difficulties, sweating, numbness or heart palpitations.
  • When the procedure has been completed, you will be removed from the scanner.
  • If an IV line was inserted for contrast administration, the line will be removed.
  • While the CT procedure itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure, such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

What happens after a CT scan?

  • If contrast media was used during your procedure, you may be monitored for a period of time for any side effects or reactions to the contrast, such as itching, swelling, rash or difficulty breathing.
  • If you notice any pain, redness and/or swelling at the IV site after you return home following your procedure, you should notify your doctor, as this could indicate an infection or other type of reaction.
  • There is typically no special type of care required after a CT scan. You may resume your usual diet and activities unless your doctor advises you differently.
  • Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

What are some of the advances in CT technology?

Advances in CT technology include:

  • High-resolution CT: This type of CT scan uses very thin slices (less than 0. 1 inches), which are effective in providing greater detail in certain conditions, such as lung disease.
  • Helical or spiral CT: During this type of CT scan, both the patient and the X-ray beam move continuously, with the X-ray beam circling the patient. The images are obtained much more quickly than with standard CT scans. The resulting images have greater resolution and contrast, providing more detailed information. Multidetector-row helical CT scanners may be used to obtain information about calcium buildup inside the coronary arteries of the heart.
  • Ultrafast CT (also called electron beam CT): This type of CT scan produces images very rapidly, thus creating a type of “movie” of moving parts of the body, such as the chambers and valves of the heart. This scan may also be used to obtain information about calcium buildup inside the coronary arteries of the heart, but the helical scanners are much more common.
  • Computed tomographic angiography (CTA): Angiography (or arteriography) is an X-ray image of the blood vessels. A CT angiogram uses CT technology rather than standard X-rays or fluoroscopy to obtain images of blood vessels — for example, the coronary arteries of the heart.
  • Combined positron emission tomography and CT (PET/CT): The combination of CT and positron emission tomography technologies into a single machine is referred to as PET/CT. PET/CT combines the ability of CT to provide detailed anatomy with that of PET to show cell function and metabolism in order to offer greater accuracy in the diagnosis and treatment of certain types of diseases, particularly cancer. PET/CT may also be used to evaluate conditions such as epilepsy, Alzheimer’s disease and coronary artery disease.

Purpose, Procedure, Risks, Side-Effects, Results

Written by WebMD Editorial Contributors

  • How Do CT Scans Work?
  • How Are CT Scans Done?
  • What Is It Used For?
  • What Is a CT Scan with Contrast?
  • Are There Any Risks?
  • What Are the Side Effects?
  • More

A computed tomography (CT or CAT) scan allows doctors to see inside your body. It uses a combination of X-rays and a computer to create pictures of your organs, bones, and other tissues. It shows more detail than a regular X-ray.

You can get a CT scan on any part of your body. The procedure doesn’t take very long, and it’s painless.

They use a narrow X-ray beam that circles around one part of your body. This provides a series of images from many different angles. A computer uses this information to create a cross-sectional picture. Like one piece in a loaf of bread, this two-dimensional (2D) scan shows a “slice” of the inside of your body.

This process is repeated to produce a number of slices. The computer stacks these scans one on top of the other to create a detailed image of your organs, bones, or blood vessels. For example, a surgeon may use this type of scan to look at all sides of a tumor to prepare for an operation.

You’d probably get a scan at a hospital or radiology clinic. Your doctor might tell you not to eat or drink for a few hours before the procedure. You may also need to wear a hospital gown and remove any metal objects, such as jewelry.

A radiology technologist will perform the CT scan. During the test, you’ll lie on a table inside a large, doughnut-shaped CT machine. As the table slowly moves through the scanner, the X-rays rotate around your body. It’s normal to hear a whirring or buzzing noise. Movement can blur the image, so you’ll be asked to stay very still. You may need to hold your breath at times.

How long the scan takes will depend on what parts of your body are being scanned. It can take anywhere from a few minutes to a half-hour. In most cases, you’ll go home the same day.

Doctors order CT scans for a long list of reasons:

  • CT scans can detect bone and joint problems, like complex bone fractures and tumors.
  • If you have a condition like cancer, heart disease, emphysema, or liver masses, CT scans can spot it or help doctors see any changes.
  • They show internal injuries and bleeding, such as those caused by a car accident.
  • They can help locate a tumor, blood clot, excess fluid, or infection.
  • Doctors use them to guide treatment plans and procedures, such as biopsies, surgeries, and radiation therapy.
  • Doctors can compare CT scans to find out if certain treatments are working. For example, scans of a tumor over time can show whether it’s responding to chemotherapy or radiation.

In a CT scan, dense substances like bones are easy to see. But soft tissues don’t show up as well. They may look faint in the image. To help them appear clearly, you may need a special dye called a contrast material. They block the X-rays and appear white on the scan, highlighting blood vessels, organs, or other structures.

Contrast materials are usually made of iodine or barium sulfate. You might receive these drugs in one or more of three ways:

  • Injection: The drugs are injected directly into a vein. This is done to help your blood vessels, urinary tract, liver, or gallbladder stand out in the image.
  • Orally: Drinking a liquid with the contrast material can enhance scans of your digestive tract, the pathway of food through your body.
  • Enema: If your intestines are being scanned, the contrast material can be inserted in your rectum.

After the CT scan, you’ll need to drink plenty of fluids to help your kidneys remove the contrast material from your body.

CT scans use X-rays, which produce ionizing radiation. Research shows that this kind of radiation may damage your DNA and lead to cancer. But the risk is still very small — your chances of developing a fatal cancer because of a CT scan are about 1 in 2,000.

But radiation’s effect adds up over your lifetime. So your risk increases with every CT scan you get. Talk to your doctor about the procedure’s potential dangers and benefits, and ask why the CT scan is necessary.

Ionizing radiation may be more harmful in children. That’s because they’re still growing. They also have more years to get exposed to radiation. Before the procedure, you may want to ask the doctor or technician if the CT machine’s settings have been adjusted for a child.

Tell your physician if you’re pregnant. If you need imaging for your stomach area, your doctor may recommend an exam that doesn’t use radiation, such as an ultrasound.

Some people are allergic to the contrast materials. Most of the time, the reaction is mild. It can lead to itchiness or a rash. In very few cases, the dye may trigger a life-threatening reaction. For this reason, your health care provider may want to monitor you for a short period after your CT scan. Tell your doctor about any allergies you have to medications, seafood, or iodine.

Your doctor should know, too, if you have diabetes and are taking the drug metformin. They’ll let you know if you should stop taking your medication before or after your procedure.

Although it’s rare, contrast materials can lead to kidney problems. Let your doctor know if you have any kidney issues before the CT scan.

Top Picks

Laser scanning of buildings: a practical demonstration

3D scanners

Construction and architecture

Experts recommend

Author: Yuri Filtsev

Author: Yuri Filtsev

Equipment set | Preparing to scan | Getting Started with a 3D Scanner | Scanning process | Import and data processing | Results

Measuring a building with a 3D surveying laser scanner is fast, convenient, simple, and much more efficient than traditional survey methods. You will be convinced of this right now: we will show step by step the process of digitizing an object and primary processing of the received data, and dwell on the advantages and individual nuances of using ground-based laser scanning.

Recall that ground-based 3D scanners and specialized software will optimize the solution of the following tasks:

  1. reconstruction and redevelopment of buildings and premises;

  2. restoration of cultural heritage sites;

  3. reverse engineering of large-sized products and equipment;

  4. reconstruction of engineering network models;

  5. geometry deviation control;

  6. BIM modeling.

Want to see if 3D technology can help you solve your problems? Order a test scan and equipment demonstration!

For the scanning demonstration, we chose the Memorial Mosque on Poklonnaya Hill in Moscow, not far from the iQB Technologies office. Our goal is to obtain a digital model of the entire facade of the object.

Standard equipment set:

  • FARO Focus S150 3D scanner in a case;

  • tripod for the scanner;

  • additionally: a set of spheres and tripods for them.

It’s not that spheres are critical for this object – we used them more to show the use of additional accessories.

Preparing for scanning

Installation of 3D scanner and spheres

At the beginning of our survey, we set four spheres, which will be the base ones. We use the remaining five as moving targets, rearranging them along with the scanner. In this case, it is necessary to ensure that the neighboring stations have at least three targets in the scanning area.

This is how the spheres look in the installed form:

Here I show the quick-release fasteners, thanks to which the scanner is easily fixed:

Getting Started with 3D Scanner

Creating a project and setting up

The first thing we do when we start working with a scanner is to create a project and give it a name. A project can be hierarchical, i.e. write data to an existing project or create a new one.

Project Structure Hierarchy:

In this step, we enable additional controls. Since we are working in an open area, we turn on the GPS. Satellite data allows you to position the stations, and their subsequent stitching will be greatly simplified.

The following settings are scanning density, filtering quality, and various camera settings. All this is done quite quickly, easily, and in principle, we are already ready to start scanning.

Then just press the “Start” button.

Scan process

The device makes revolutions around its axis, measures the distance, records angles, takes photographs – all in automatic mode.

Upon completion of the scan, we will be given a panoramic image, on which we can specify additional markers, complete them, or scan any particular area.

This is how the completion of the scanning stage at the station looks like:

If no additional settings are required, click the “Next” button and transfer the scanner to a new point.

At the station, we try not to get into the target of the device, so as not to create unnecessary interference. The gate is a slot in its middle:

In fact, the process of work, if the settings have already been entered, is simply to transfer the scanner, press “Start” and see that the device is not stolen from us. This is fundamentally different from working with a total station. Hands do not freeze (we worked at minus 12-15 degrees and a fairly strong wind). Working with a stylus in such conditions would not be very convenient.

We will later see these data live on the project itself. Here I wanted to show the photorealism of the point cloud that the scanner collects. Here is a fragment of a point cloud with a complex decoration on the facade of a building:

In the next photo, pay attention to the comrades from behind, they actively participated in the process, they created a certain problem for us in our work. On the cloud of points, then we will evaluate the degree of their participation.

The approximate distance between stations is 10-15 meters. The time at the station depends on the settings we choose, i.e. whether we shoot in color, without color, whether we use HDR.

This is probably the only device that I have come across with photographic settings and a choice of color exposure. FARO puts a lot of emphasis on photorealistic images and their visualization.

We are approaching the final – we return to the same point from which we started, thus closing the circle. In total we made 21 stops.

You can follow the work done on scanning the mosque on the video:

Primary data processing

Data import into FARO SCENE

So, we have collected field data, we come to the office, insert the SD card into the computer, and the SCENE program prompts us to import the project. The import procedure starts. The data from the FARO scanner is quite optimized, has a low weight, but nevertheless, this procedure takes some time. Also, processing and directly stitching the point cloud itself takes a significant amount of time.

Specifications of Project PC

Resource-intensive processes are very dependent on the capacity of the computer. Here are my PC specs:

  • i5 processor with a frequency of 3 GHz on four cores,

  • 14nm process technology and 4th generation architectural obsolescence;

  • 16 GB of RAM;

  • HDD with 7200 rpm torque.

Very average system for such tasks.

Importing a 4 GB project and processing took 10 minutes, stitching scans took 25 minutes, since we worked with GPS and spheres.

If the program had to structure non-positioned stations, it would take 30-40 minutes. At the same time, I saw cars that will assemble the same project 5 minutes before the final result. These moments are individual, but FARO allows you to work even on mediocre computers.

The transfer is over, and then we go into our project. I changed the title – image, project name.

Processing settings configuration

Let’s move on to processing. Its settings are quite extensive: coloring, distance filter, clipping filter, various noise reduction filters.

Scan selection (distribution of stations by clusters)

In this project, I shot in two clusters, in different presets, so now I determine which stations I will assign to which cluster.

I create the first and second clusters:

Filter selection per cluster

Next, I drag the stations in the order I need. When processing, I apply my own settings to each cluster.

Be sure to check the “Find Spheres” box, as we worked with them.

Then we repeat the processing procedure for the second group. This is how the process of primary filtering of our data looks like.

We also suggest that you familiarize yourself with the processing stage on the video:

So, let’s see how much time we spent:

  • scanning, taking into account reconnaissance and forced downtime: 2.5 hours;

  • project import and pre-processing: 10 minutes;

  • stitching scans: 25 minutes.

In one of the publications, we plan to take a closer look at the functionality of the FARO SCENE software, which is used to merge scans and form a point cloud.

For further modeling based on terrestrial laser scanning data, you can use the following FARO software products:

  1. As-Built (including plugins for AutoCAD and Revit) – for CAD and BIM design. The software allows you to make dimensional drawings and build BIM models with reference to a point cloud and is designed to expand the functionality of AutoCAD and Revit.

  2. BuildIT Construction – for quality control, that is, for comparing scan data with design documentation.

Article published on 03/24/2022, updated on 01/31/2023

Laser scanning for the preservation of cultural heritage sites and restoration work – Services on vc.ru

There is a huge number of cultural heritage sites. To preserve the appearance of the building, designers and architects must have detailed dimensional drawings of the object, including facades. The absence of a building project and facade drawings is a common situation that needs to be addressed.


Thanks to 3D laser scanning, architectural measurements and modeling are faster, more accurate and more detailed than ever before. We are excited to bring these industry-changing services to today’s architects, led by a team that has extensive experience in laser scanning, modeling and data management.

Fig. 1 Digital 3d models of buildings on the street. Volkova Kazan

There is a practice of laser scanning of historical and cultural heritage sites for the purpose of preserving digital copies.

A major fire at Notre Dame Cathedral in Paris on 15 April 2019 affected people around the world. Notre Dame has been documented inside and out using laser scanning to the nearest millimeter. Architectural historian Andrew Tallon, who died in 2018, scanned the cathedral in 2010. The cathedral has been scanned and over a billion data points have been collected, which are an exact 3d replica of the intact church. This data is used to restore the object.

Vladimir Serkov is a professional surveyor, entrepreneur and expert in the field of laser scanning, engaged in similar activities in Kazan.

“During my career, I voluntarily scanned several buildings in the city for the purpose of preserving digital copies of objects. The obtained data on laser scanning can be transferred to organize the Digital Archive of copies of buildings and for the purposes of teaching how to work with modern data. Further work on laser scanning of objects is planned”

Fig. 2 Digital 3d model of the building Kazan Family Center

Terrestrial laser scanning is a non-contact technology for determining the spatial coordinates of object surface points using a laser scanner. Due to its versatility and a high degree of automation of measurement processes, a laser scanner is not just a geodetic instrument, a laser scanner is a tool for quickly solving a wide range of applied engineering problems. That is why laser scanning has found its application in the construction industry. It is simply impossible to obtain such a volume of qualitative and quantitative information on a construction site by other methods.

Fig.3. Trimble laser scanner in operation Kazan

Fig. 4. Digital 3d models of buildings on the street.