Diagnostic technology and planning

CT or MRI? Differences, uses and Italian requirements

CT and MRI are neither competitors nor interchangeable examinations: they answer different questions. This overview explains how they work, when each is commonly selected and what Italian rules actually require when a facility installs whole-body MRI.

By Spinergy Medical 07 September 2026 17 min read

CT and magnetic resonance imaging can both show structures inside the body, often as cross-sectional images and three-dimensional reconstructions. The scanners may even look similar from outside. However, the way they create an image, the tissues they represent best, acquisition time, safety precautions and infrastructure are fundamentally different.

The useful question is not “which scanner is better?” but which modality best answers this clinical question for this person at this time. In an emergency, CT speed may be decisive. In another setting, MRI may provide much more informative soft-tissue contrast. One examination may remove the need for the other, while complex pathways may use them as complementary sources of information.

There is also a separate question for organisations planning or expanding an imaging centre: does an Italian facility have to have a CT scanner when it installs a whole-body MRI? In short, CT availability is the standard national requirement for non-dedicated MRI systems up to 4 tesla, but the rules allow each Region to regulate an exemption based on integration with nearby facilities. This does not always amount to a requirement to buy and own a CT scanner in the same centre.

Do CT and CAT mean the same thing?

In English, CT means Computed Tomography. The older expression CAT, Computed Axial Tomography, is still understood, just as TAC remains common in Italian. CT is now the more precise term because modern systems acquire volumetric information that is not limited to the axial plane.

This article uses CT for the scanner and examination, MRI for magnetic resonance imaging, and RM when reproducing terminology used in Italian legislation.

CT and MRI use different physical principles

Aspect	CT	Magnetic resonance imaging
Energy used	X-rays	Static magnetic field, gradients and radiofrequency
Ionising radiation	Yes	No
Image formation	Multiple X-ray projections are processed into slices and volumes	The system detects signals from nuclei, mainly hydrogen, following radiofrequency excitation
Frequent strengths	Speed, lung, bone, calcification, trauma and acute bleeding	Soft-tissue contrast, nervous system, joints, muscles and many organ-characterisation tasks
Sensitivity to motion	Generally lower because acquisition is rapid	Generally higher because many sequences require stillness and cooperation
Main precautions	Radiation justification and dose optimisation; possible iodinated contrast	Screening of people, implants and objects; noise, heating and possible gadolinium contrast

This table describes broad patterns, not an imaging prescription. Technology, protocols and applications evolve, and selection always depends on the clinical question.

How CT produces an image

A CT scanner rotates an X-ray tube around the patient. Detectors measure how the beam is attenuated as it passes through different tissues. A computer processes numerous projections and reconstructs slices, different planes and three-dimensional volumes.

The National Institute of Biomedical Imaging and Bioengineering description of CT explains this distinction: CT is not one conventional radiograph, but a set of measurements acquired around the body and reconstructed mathematically.

Speed is one of CT’s major advantages. In many applications, the data are acquired in seconds. This matters when a patient cannot remain still, when a breath-hold must be short or when an urgent condition needs a rapid answer.

How MRI produces an image

MRI does not use X-rays. A strong magnetic field aligns some of the hydrogen nuclei in tissue; radiofrequency pulses temporarily change their state and gradients provide spatial encoding. As the nuclei return towards equilibrium, the system detects signals that vary with tissue properties and sequence design.

The result is not a “magnetic photograph”. It is a reconstruction of physical signals that can be weighted in many ways. This flexibility explains why MRI often distinguishes water, fat, muscle, ligaments, white and grey matter, marrow and other soft tissues in considerable detail. NIBIB describes MRI physics and its main applications.

Ionising radiation versus magnetic field

The best-known distinction is correct: CT uses ionising radiation and MRI does not. That statement alone cannot determine which examination is more appropriate or safer for a particular person.

CT uses ionising radiation

X-rays have enough energy to ionise matter. Medical exposure must therefore be justified by its diagnostic benefit and optimised: the necessary information should be obtained with a dose that is reasonably as low as possible while preserving the required image quality.

In Italy these principles are established by Legislative Decree 31 July 2020, no. 101. Articles 157 and 158 prohibit unjustified exposure and require dose to be kept as low as reasonably achievable while remaining compatible with the diagnostic information needed.

A CT dose is not one fixed number. It varies with body region, protocol, coverage, number of phases, body size, age and scanner technology. Comparing examinations using only the word “CT” is therefore not meaningful. A targeted, optimised protocol is not equivalent to an extended or multiphase study.

Radiation does not make CT an examination to refuse when it is clinically indicated. The FDA explains that the benefit of an appropriate X-ray examination generally outweighs the small radiation risk. The objective is to avoid unnecessary exposure, duplicate studies and unsuitable protocols, not to lose information that may alter diagnosis or treatment.

MRI does not use ionising radiation, but it still requires safety controls

Saying that MRI “has no radiation” is an oversimplification. More precisely, it uses no ionising radiation. It employs a static magnetic field, time-varying gradient fields and radiofrequency energy. These do not create the same radiation risk as X-rays, but they introduce different hazards and precautions.

The field may attract ferromagnetic objects. Devices and implants can experience force, heating or malfunction. Gradients produce intense acoustic noise and may cause stimulation, while radiofrequency deposits energy in tissue. People, trolleys, cylinders, accessories and devices therefore require screening before they enter controlled areas.

An implant does not automatically exclude MRI. Its manufacturer, model and conditions of use must be identified. An MR Conditional device can be scanned only when every stated condition is met. An object or device of unknown status must not be assumed compatible. The FDA summarises MRI-specific benefits and risks.

When is CT commonly selected?

CT is often selected when speed and the representation of particular structures are priorities. Frequent examples include:

initial assessment of many major traumas;
investigation of acute bleeding, depending on region and presentation;
lung and chest imaging;
complex fractures, cortical bone and calcification;
stones in selected organ systems;
rapid assessment of chest, abdomen and pelvis in many acute conditions;
CT angiography of vessels and the aorta when indicated;
planning or guidance of selected procedures.

CT can cover large body regions rapidly and is less vulnerable to some types of motion. It is also often easier to manage when an implanted device’s MRI status has not yet been established. This does not make it the automatic first choice for every pain, trauma or suspected diagnosis.

When is MRI commonly selected?

MRI is often preferred when soft-tissue contrast is central or when sequences need to describe different properties of the same tissue. Common applications include:

brain, spinal cord and nerves;
menisci, cartilage, ligaments, tendons and muscles;
bone marrow and many joint conditions;
characterisation of selected findings in the liver, pancreas, biliary system, pelvis and other organs;
specialist cardiac and vascular imaging;
oncological or functional assessments where MRI sequences add information;
repeated follow-up when MRI is clinically suitable and a new ionising exposure can be avoided.

MRI normally takes longer and is more sensitive to movement. Claustrophobia, pain, breathing difficulty or an inability to hold position may influence feasibility and quality. Some patients may require additional management, which introduces its own resources and risks.

CT or MRI: examples by clinical area

General scenario	Why CT may be selected	Why MRI may be selected
Trauma and emergency	Rapid answer, broad coverage, bone, chest and bleeding assessment	Further assessment of cord, ligaments, soft tissue or unresolved lesions when time and stability allow
Brain	Often an urgent first assessment, particularly to exclude certain haemorrhages	Greater detail for many tissue abnormalities, ischaemia in selected settings and selected follow-up
Spine	Bone and vertebral trauma	Spinal cord, discs, roots, ligaments and soft tissue
Chest and lung	Principal modality for many lung-parenchyma assessments	Selected applications involving mediastinum, heart, vessels or specific questions
Bone and joints	Complex fractures, cortex and calcification	Marrow, cartilage, menisci, ligaments, tendons and muscles
Abdomen and pelvis	Speed and broad overview, especially in many acute conditions	Tissue characterisation and specialist organ or pelvic protocols
Vessels	Fast CT angiography with high spatial resolution in many applications	MR angiography and functional assessment in selected cases, sometimes without contrast
Oncology	Staging and follow-up in many diseases	Characterisation and local staging of selected organs and tumours

These are orientation examples. The referrer and radiologist choose the modality using guidelines, symptoms, urgency, age, prior imaging, contraindications and availability. The same body region may need different protocols and, in some pathways, both modalities.

Contrast media: iodine for CT and gadolinium for MRI

Neither CT nor MRI always requires contrast. When it is needed, CT generally uses iodinated media and MRI usually uses gadolinium-based agents. They are not interchangeable and have different indications and precautions.

Assessment considers the clinical question, renal function, previous reactions, medicines and individual conditions. Certain thyroid conditions may also matter for iodinated contrast. For gadolinium agents, the type of agent and severe renal impairment require particular attention. “No ionising radiation” does not automatically mean “no contrast” or “no risk”.

Patients should always report previous reactions, renal disease, possible pregnancy and documentation for implants or devices. The professionals responsible for the examination decide whether contrast is required.

Children, pregnancy and implanted devices

Children’s greater radiation sensitivity and longer life expectancy make CT optimisation and consideration of suitable alternatives particularly important. MRI avoids ionising radiation, but young children may find it difficult to remain still and can occasionally require sedation or anaesthesia. That also forms part of the overall risk-benefit assessment.

The imaging facility must be told about a possible or confirmed pregnancy before the examination. CT may still be performed when clinically necessary, using the required justification and optimisation. MRI also needs medical assessment of the indication, stage of pregnancy and possible contrast even though it does not use ionising radiation.

Pacemakers, neurostimulators, cochlear implants, pumps, clips, prostheses and other devices should not be described generically as “MRI compatible”. Exact identification and comparison with the manufacturer’s stated conditions are required.

“Whole-body MRI” does not necessarily mean a head-to-toe examination

In equipment terminology, a whole-body MRI scanner is a system that is not restricted to a small anatomical region and can examine multiple body areas using suitable coils and protocols. It does not mean that every patient receives a single head-to-toe scan.

A whole-body examination is a specific clinical protocol with its own indications, limitations and duration. The fact that a scanner is whole-body describes its class and versatility; it does not justify general screening or replace targeted examinations.

This distinction matters in Italian regulation as well. The additional-equipment requirement applies to non-dedicated MRI equipment, not to whether an individual patient receives a whole-body examination.

Is CT mandatory when an Italian facility installs whole-body MRI?

The short answer

For Italian clinical installations of non-dedicated MRI with a static field up to 4 T, a CT scanner is part of the standard equipment required at the authorised healthcare facility. However, national rules allow each Region to waive the presence of CT when regulated integration with nearby diagnostic-imaging facilities is in place.

Therefore:

it is inaccurate to say that anyone buying MRI must always buy CT as well;
it is equally inaccurate to say that CT is not a requirement;
the competent Region’s implementation of the equipment requirement and any exemption must be checked before investment.

What the Italian Ministerial Decree of 14 January 2021 says

Section A of the annex to the Ministerial Decree of 14 January 2021 in the Italian Official Gazette states that MRI equipment, excluding dedicated systems, may be installed in public or private facilities authorised under regional requirements and equipped with:

a computed-tomography scanner;
conventional radiography equipment;
an ultrasound scanner.

The annex then allows Regions to waive the need for the presence of CT where integration with nearby diagnostic-imaging facilities is established and regulated.

The exemption is not automatic and cannot be created by an informal understanding. Distance, effective patient management, documentation, authorisations and the form of the link depend on applicable regional measures. Regions may establish more specific or restrictive conditions for particular field strengths and types of facility.

“Having CT” does not necessarily mean owning the asset

The decree refers to a facility being equipped and to its authorisation requirements. It does not make civil ownership of the scanner the only issue, nor does it use the expression “in the same building”: the relevant facility perimeter is the one recognised through the authorisation process. Purchase, lease, rental, service or another form of availability cannot, however, be assumed equivalent: title, location, operating authorisation and continuity of availability must comply with regional rules.

Where an exemption is used, the question is not who owns the CT scanner, but whether integration with the nearby facility is expressly permitted, regulated, formalised and suitable for patient management.

The facility requirement does not mean every MRI patient must also undergo CT

Technology availability and clinical appropriateness are separate issues. A CT scanner in the centre, or a formal link to another centre, does not mean that CT must be performed before or after every MRI. Every ionising exposure requires its own clinical justification.

The organisational requirement recognises that the modalities are complementary and that an imaging centre must manage questions, contraindications and pathways that MRI alone does not cover. It does not create a mandatory examination sequence for patients.

Dedicated MRI systems are a different case

The January 2021 decree defines a category of new-generation dedicated MRI systems that are not subject to the same authorisation when the stated conditions are all met, including a field no greater than 0.5 T, a non-superconducting magnet and the uses specified by the decree.

A scanner does not enter this exception merely because marketing calls it “open” or “dedicated”. Configuration, field, technology and intended use must be compared with the decree and regional rules.

Why a facility may need both modalities

CT and MRI are not duplicate investments. They provide different information and respond to different constraints:

CT can rapidly support emergency, lung, bone and many vascular or abdominal pathways;
MRI can add soft-tissue, nervous-system, joint and advanced characterisation;
an MRI contraindication may require another modality;
the first modality may identify a finding that the second characterises more fully;
availability, timing and the patient’s condition may alter the pathway.

For a healthcare organisation, this complementarity affects catchment area, staffing, reporting, operational continuity and investment sustainability. Installing MRI is not only a choice of tesla, bore and gradients; it means integrating it within an authorised and organised imaging centre.

What to verify before buying or installing MRI in Italy

Before committing the budget or finalising a layout, the organisation should verify at least:

the exact equipment classification: dedicated, non-dedicated, fixed or mobile;
magnetic-field strength and the corresponding authorisation pathway;
regional health planning and requirements;
the facility’s existing diagnostic-imaging authorisations;
presence and authorisation of CT, conventional radiography and ultrasound;
whether the Region permits a CT exemption and under which integration conditions;
rooms, routes, shielding, systems, controlled zones and emergency management;
staffing, safety appointments, quality controls and organisational model;
installation, maintenance, energy, cryogenic and continuity costs;
documentation required before and after installation.

The Italian Ministry of Health summarises the authorisation framework for MRI equipment and the role of Regions and Autonomous Provinces for systems up to 4 T. Early confirmation with the competent authority avoids designing a technically sound site that does not fit the local authorisation pathway.

Common myths about CT and MRI

“MRI is always better than CT”

No. It often provides greater soft-tissue contrast, but may be less suitable for lung, calcification, many emergencies or patients unable to remain still. “More detail” only makes sense for a defined tissue and clinical question.

“CT is dangerous because it uses radiation”

An unjustified CT exposure should be avoided. A clinically appropriate and optimised CT may provide a benefit far greater than the radiation risk. The risk should neither be denied nor turned into alarmism.

“MRI is risk-free”

It uses no ionising radiation, but magnetic field, gradients, radiofrequency, devices, ferromagnetic objects and contrast media require specific procedures and expertise.

“If the centre must have CT, every patient needs both scans”

No. The requirement concerns facility equipment and authorisation. The clinical indication for every examination remains individual.

“Whole-body means every scan covers the patient from head to toe”

No. In equipment terminology, it means that the scanner is not limited to a small anatomical region. A whole-body examination is a separate protocol requiring its own indication.

Frequently asked questions about CT and MRI

Which examination is more accurate, CT or MRI?

It depends on the target. CT may be more informative for lung, bone, calcification and many emergencies. MRI may be more informative for the brain, cord, joints and other soft tissues.

Does MRI emit radiation?

It does not use ionising radiation. It does use magnetic fields and radiofrequency energy and requires specific safety controls.

How much radiation does a CT scan deliver?

There is no single value. Dose depends on the body region, protocol, coverage, phases, patient and technology. Any figure must refer to a specific examination.

Can CT and MRI be used in the same pathway?

Yes, when each answers a justified clinical question. They may be alternatives or provide complementary information.

Can a person with a pacemaker undergo MRI?

It depends on the implanted system and its stated conditions. Exact device identification and the facility’s appropriate pathway are required; knowing only that it is “recent” is not sufficient.

Must a facility buy CT before opening whole-body MRI in Italy?

CT is the standard equipment required by the January 2021 decree for non-dedicated MRI up to 4 T. A Region may regulate an exemption where there is formal integration with a nearby facility. Purchase and ownership are therefore not the only possible framework, but advance regional verification is essential.

Does the national exemption apply automatically throughout Italy?

No. The decree gives Regions the power to grant and regulate the exemption. The competent Region’s implementation and documentation requirements must be checked.

Support for selecting, installing and integrating CT and MRI systems

Spinergy Medical can support healthcare organisations and investors with the technical assessment of CT and MRI systems, preliminary site and infrastructure review, installation or deinstallation planning and coordination of specialist activities.

Explore our services for MRI installation planning, CT installation planning and technical consulting. For a new imaging centre, assessment should begin before the scanner is selected: call or email us to define the equipment, site and project pathway.

Medical and legal information notice

Regulatory information: this summary is provided solely for general information, is updated to 7 September 2026 and does not constitute legal, regulatory or authorisation advice or a binding interpretation of Italian law. Laws and administrative measures may change, so the version in force at the date of the project must always be checked. This article does not certify the compliance of an individual site, replace an authorisation decision or confirm that a regional exemption applies. Requirements and procedures also depend on the Region, facility configuration, whether the MRI system is classified as dedicated or non-dedicated, fixed or mobile, its field strength and the applicable authorisation documents. Before purchasing, installing or placing an MRI or CT system into clinical service, the specific case must be reviewed with qualified professionals and the authority or authorities identified by the applicable national and regional rules.

Medical information: the clinical content of this article does not replace a prescription or medical assessment. The appropriate examination must be selected by healthcare professionals according to the individual clinical question and patient circumstances.