Nuclear medicine

Nuclear medicine is the branch of medicine concerned with the use of radionuclides to diagnose and treat diseases. These radionuclides, called radiopharmaceuticals, are used for the assessment of organ function, detection of diseases, treatment of some diseases, and monitoring the effects of treatment. Nuclear medicine procedures are able to pinpoint molecular activity within the body, they offer the potential to identify disease in its earliest stages as well as a patient’s immediate response to therapeutic interventions.

For diagnosis, the procedures for nuclear medicine imaging are noninvasive, except intravenous injections. They are usually painless medical tests that help physicians diagnose and evaluate medical conditions. These imaging scans use radiopharmaceuticals or radiotracers.

Depending on the type of nuclear medicine exam, the radiotracer is injected into the body, swallowed or inhaled as a gas and eventually accumulates in the organ or area of the body being examined.

In many centers, nuclear medicine images can be superimposed with computed tomography (CT) or magnetic resonance imaging (MRI) to produce special views, a practice known as image fusion or co-registration. These views allow the information from two different exams to be correlated and interpreted in one image, leading to more precise information and accurate diagnoses. In addition, manufacturers are now making single photon emission tomography/computed tomography (SPECT/CT) and positron emission tomography/computed tomography ({PET/CT) units that are able to perform both imaging exams at the same time.

Nuclear medicine also offers therapeutic procedures, such as radioactive iodine (I-131) therapy that use small amounts of radioactive material to treat cancer and other medical conditions affecting the thyroid gland, as well as treatments for other cancers and medical conditions.

Radioimmunotherapy (RIT) is a personalized cancer treatment that combines radiation therapy with the targeting ability of immunotherapy, a treatment that mimics cellular activity in the body’s immune system.


Radiopharmacy is concerned with the pharmaceutical, chemical, physical, biochemical, and biological aspects of radiopharmaceuticals. It requires an understanding of the design, preparation, quality control, management, storage, dispensing, and proper use of radiopharmaceuticals.

A radiopharmaceutical is a radioactive compound used for the diagnosis and therapeutic treatment of human diseases. In nuclear medicine, nearly 95% of the radiopharmaceuticals are used for diagnostic purposes, while the rest are used for therapeutic treatment. Radiopharmaceuticals usually have minimal pharmacologic effect, because in most cases they are used in tracer quantities (Saha, 2004). There is no dose-response relationship in this case, which thus differs significantly from conventional drugs.

A radiopharmaceutical can be a radioactive element such as 133Xe, a simple salt such as 131I-NaI, or a labeled compound such as 131I-iodinated proteins and 99mTc-labeled compounds.

Typically, radiopharmaceuticals contain at least two major components:


Chemical compound (non-radioactive component)

Defines the physical parameters such as physical half-life (phyT1/2) and type of radiation for diagnosis or therapy

Determine the in vivo distribution and physiological behavior of the radiopharmaceutical.

The utility of a radiopharmaceutical is dictated by the characteristics of these two components.

Radioactive Decay

Radionuclides are unstable nuclei to varying degrees, and become stable upon radioactive decay. The more unstable a radionuclide is, the faster it decays. Approximately 3000 nuclides have been discovered so far; most of these are unstable, but only about 30 of these are routinely used in nuclear medicine.

When a radionuclide goes through decay, it emits different forms of ionizing radiation: alpha (α), beta (β), or gamma (γ) radiation. Depending on the radiation property of the radionuclide, the radiopharmaceutical is used either for diagnosis or for therapy. Diagnostic radiopharmaceuticals decay by gamma emission or positron emission, while therapeutic radiopharmaceuticals, these shdecay by particulate decay (alpha or beta) since the intended effect is in fact radiation damage to specific cells.

Alpha decay is characterized by the emission of an alpha particle from the nucleus. This particle is a helium ion containing two protons and two neutrons. Alpha particles are unable to penetrate the outer layer of dead skin cells, but are capable, if an alpha emitting substance is ingested in food or air, of causing serious cell damage. Smoke detectors work by alpha decay, they contain an ionization chamber which consists of a positive and negative electrode along with a very small amount of radioisotope Americium-241. When smoke particles enter the detector, the alpha particles released by the americium atoms in alpha decay are caught by smoke particles, which triggers the detector’s alarm system.

Beta radiation takes the form of either an electron or a positron (a particle with the size and mass of an electron, but with a positive charge) being emitted from an atom.  It can penetrate skin a few centimeters, posing somewhat of an external health risk. However, the main threat is still primarily from internal emission from ingested material.  Beta emitting radioisotopes can be used to monitor the thickness (gauge) of a sheet of material. Radionuclide therapy (RNT) or radiotherapy is a cancer treatment that works by utilizing beta decay using the radioisotopes Lutetium-177 or Yttrium-90. These radioisotopes are attached to a molecule and ingested. As the radioactive atoms decay, they release beta particles and kill the nearby cancer cells.

Gamma (γ) radiation is characterized as electromagnetic radiation. When used in diagnostic radiopharmaceuticals, the finally produced gamma rays is powerful enough to be detected outside the body of the patient. Unlike alpha or beta, gamma radiation does not consist of any particles, instead, it consist of a photon on energy emitted from an unstable nucleus.

Formulation and Production of Radiopharmaceuticals

The potential hazard of the product to the patient and to the professional responsible for production should be in mind when designing a radiopharmaceutical. The goal must be to have a maximum amount of photons with a minimum radiation exposure of the patient.


For conventional radiopharmaceuticals used in diagnosis, it is favorable to use products with short half-lives. Radionuclide generators are widely used for the supply of short-lived radionuclides/ radiopharmaceuticals. Several generator systems are available and routinely in use within nuclear medicine. Because of the short half-life, the coupling of the radionuclide to the carrier molecule must be done immediately before administration. Hence there is a need to have a constant supply of carrier molecules that can be labeled efficiently on site. For this purpose, several preparation kits have been developed. The function of the carrier molecule in a radiopharmaceutical is to carry the radioactivity to the target organ, and to make sure the radioactivity stays there. The uptake of radioactivity should be as specific as possible, in order to minimize irradiation of other organs and parts of the body. This is particularly important when using radiopharmaceuticals for therapy. For diagnostics, it is desirable that the radiopharmaceutical is localized preferentially in the organ under study since the activity from non-target areas can obscure the structural details of the pictures of the target organ. It is therefore important to know the specific uptake in an organ for a potential chemical carrier, and also the rate of leaking out of the organ/organ system. Thus, the target-to-background activity ratio should be large.

The manufacture of radiopharmaceuticals is potentially hazardous regardless if it is small-scale or large-scale. The operations must take place on premises that is designed, constructed, and maintained for the specific type of product. The radionuclides must only be used in specially designed and approved “radioisotope laboratories”, as stipulated by the regulations on radiation protection. National regulations with regard to the design and classification of radioisotope laboratories must be strictly followed. Such laboratories are normally classified according to the amount of the various radionuclides to be handled at any time, and the radiotoxicity grading given to each radionuclide. (EANM, 2008)

Premises must be designed with two important aspects in mind according to the basic principle of Good Radiopharmaceutical Practice (GRP):

  • The product should not be contaminated by the operator.
  • The operator and the environment should be protected from contamination by the radioactive product.

Preparation and Dispensing or Radiopharmaceuticals

Prior to starting the preparation and dispensing of radiopharmaceuticals, all of the materials required should be assembled and placed in or close to the contained workstation/laminar flow cabinet (LAFC). All vials containing radioactive materials must be shielded while handling; and vials should only be removed from their shields for assay, inspection or disposal. All syringes containing radioactive liquids must be shielded while handling, except during an assay. Unshielded vials or syringes should not be handled directly. Long handled tongs should be used to place and remove unshielded materials in the dose calibrator.

Work procedures should be designed so as to minimize exposure from external radiation and contamination. Care must be taken to prevent spillage from occurring. All manipulation for dispensing radioactive materials should be carried out over a drip tray, in order to minimize the spread of contamination due to breakages or spills. Should a spill occur then it should be cleaned up before proceeding any further. All items that might be contaminated should be removed from the affected area and stored safely. Care should be taken doing this, in order to minimize the spread of contamination. As with all spills, it is more convenient to allow natural decay to take care of the contamination, if the items are not required immediately. For those items that are needed, they should be cleaned with alcohol swabs taking care not to spread the contamination. Using multiple swabs which are then disposed is the most effective way to remove contamination.

Pharmaceuticals kits have specific instructions for reconstitution provided by the manufacturer. These instructions should be followed strictly, especially in terms of the activity and volume to be added to the kit. Recommended incubation times also vary and must be adhered to. Some radiopharmaceuticals must be refrigerated after preparation. Therefore, consideration should be given to the provision of suitably shielded refrigeration facilities. Most radiopharmaceuticals are reconstituted with Technetium-99m (99mTc). Protective caps should be removed from the pharmaceutical vials; and the vials should be placed in the appropriate labelled vial shields. The rubber septum of each pharmaceutical vial should be swabbed with alcohol, and the alcohol should be allowed to evaporate.

Radiopharmaceuticals are generally expected to conform to specifications under the following criteria:

  • Radionuclide concentration
  • Radiochemical purity
  • Chemical purity
  • Sterility
  • Apyrogenicity
  • Absence of foreign particulate matter
  • Particle size (if appropriate)
  • pH
  • Biological distribution

Blood cell labelling

Radiolabeled blood cells have played an important role as diagnostic radiopharmaceuticals for many decades. They are the drug of choice for cardiac blood pool imaging, which has resulted in an evolution of different methods of labelling.

Several blood cellular elements can be radiolabelled with different radionuclides and radiolabelling approaches for various clinical applications. Regardless of the nature of the blood cells, of the radionuclide used or of the clinical application, it is necessary to maintain both cell viability and sterility and to avoid the operator’s exposure to biological and radiation hazard during cell manipulation and radiolabelling. Strict aseptic conditions and the guidelines on current Good Radiopharmacy Practice (cGRP) in the Preparation of Radiopharmaceuticals should be followed in the manipulation and procedures of radiolabelling.  An open or closed vial system on a laboratory workbench cannot be used as an alternative to a controlled sterile environment. Cross contamination or mix-up of blood should be prevented at all times. Preparation of radiolabelled cells must be performed successively or by different people in different locations. All surfaces should be properly cleaned, decontaminated and disinfected prior to use, after all procedures are completed, and whenever surfaces are overtly contaminated. (EANM, 2008)

During radiolabelling, approved written procedures should be followed at all times. All materials used should be identified and certified for human use. Whenever possible radiochemical purity should be checked and radiolabelling efficiency (percentage of radiolabelling of cells) calculated. Before release, radiolabelled blood should be checked for aggregation of clumping of cells and for presence of particulate contamination. At regular intervals, the integrity of the cells should be ascertained by use of suitable procedures i.e. using trypan blue. Prior to administration, control of patient identity should be performed.

Clinical Applications of Radiolabelled cells and Radiolabelling approach (EANM, 2008)

Clinical application

Blood cellular element

Radionuclide/ radiolabel

Radiolabelling approach

Cardiac and vascular imaging

Red cells


In vivo

In vivo/in vitro

Gastrointestinal bleeding

Red cells


In vivo

In vivo/in vitro

Spleen imaging

Denaturated red cells


In vivo

In vivo/in vitro

Blood volume and red cell volume

Red cells

99mTc-pertechnetate 51Cr-chromate

In vitro

Red cell survival

Red cells


In vitro

Site of red blood cell destruction

Red cells


In vitro

Infection and inflammation

White blood cells




In vitro

Abnormal platelet deposition





In vitro

Radiolabelling with 99mTc

The general steps in radiolabeling blood cells with technetium are:

  1. Treatment of blood cells with stannous ion

Stannous ions are most commonly employed for the reduction of technetium to a lower oxidation state for it to firmly bind to hemoglobin. Stannous chloride, as a stannous pyrophosphate complex, is preferred.

  1. Removal of excess extracellular stannous ion

The presence of stannous ion in the serum can result in the undesirable reduction of 99mTc pertechnetate prior to its entry into the red blood cell. Only the oxidized form of 99mTc can be transported by the erythrocyte membrane.

  1. Addition of pertechnetate

Actual red blood cell labeling with 99mTc occurs whenever 99mTc pertechnetate is brought into contact with RBCs that have been previously treated with stannous ions. This can be accomplished by either the in vivo or in vitro addition of 99mTc pertechnetate to RBCs that have been pretreated with stannous ions.

 Blood Cell Labelling Isolator

There are three different approaches in radiolabeling with 99mTc, it may be by in vitro, in vivo, and combined in vivo/in vitro.

In vitro radiolabelling

In vitro radiolabelling of RBCs gives by far the highest labelling efficiency and the most stable labelling over time. It greatly simplified the labeling procedure. One major advantage was that reagents could be prepared in advance and stored while quality control testing was undertaken. This approach may be used for the determination of red cell and blood volume, and may also be employed in patients who are taking drugs which may interfere or inhibit stannous ion transport through the cell membrane such as heparin or hydralazine, resulting in lower labelling efficiency.

A small volume of anticoagulated blood, heparin or anticoagulant citrate dextrose (ACD) is incubated with an aliquot of a reconstituted stannous agent. Any excess of Sn2+ is oxidized by addition of 0.1% sodium hypochlorite and may be removed by centrifugation. The cells are separated and incubated with 99mTc-pertechnetate for 5-20 minutes with occasional mixing. After incubation, unbound activity is washed away by addition of a few milliliters of saline and centrifugation. The cells are separated and re-suspended in saline before re-injection. (EANM, 2008)

In vivo radiolabeling

This is the simplest and least time consuming radiolabelling technique. An injection of a reconstituted solution of stannous agent is followed by injection of 99mTc-pertechnetate 20-30 min later. The major disadvantage of this radiolabelling approach is a generally lower and more variable labelling efficiency. This may be due to insufficient Sn2+ incorporation into the cells which results in reduction of 99mTc-pertechnetate outside the RBC. Reduced 99mTc is then not able to diffuse across the red cell membrane, resulting in a high background activity. Low labelling yields may also be a consequence of low hemoglobin concentration and/or low hematocrit.

In vivo/in vitro radiolabeling

More variations of the in vivo/in vitro radiolabelling approach are in use. In all approaches, the intravenous administration of a stannous agent is followed by withdrawal of an aliquot 36 of pre-tinned blood 15-30 min after application. The excess of Sn2+ not incorporated into cells may be removed by centrifugation before 99mTc-pertechnetate is added to the cells. Alternatively blood may be taken into a shielded syringe containing an anticoagulant and the required amount of 99mTc-pertechnetate.The blood is then mixed with the 99mTc-pertechnetate and allowed to incubate for 5-20 min at room temperature with occasional mixing. The unbound activity is washed away by centrifugation before reinjection. Radiolabelled blood may alternatively also be re-injected without removal of unbound activity. With the later approach in which no washing step is involved one can expect lower radiolabelling efficiency and higher background activity, depending on the complexity (number of washing steps avoided) of the procedure.

 Technetium Dispensing Isolator

Radiolabelling with 51Cr

Radiolabelling of RBCs with 51Cr is carried out in vitro: 51Cr in the form of sodium chromate is incubated with whole blood containing anticoagulant citrate dextrose (ACD) for approximately 10 -15 min. Chromate ion freely diffuses into the RBCs, where it is reduced to chromic ion (Cr3+). Chromic ion bound to beta globin chain of the hemoglobin molecule is retained in the cell. The labelling process is stopped by adding ascorbic acid which reduces the chromate outside the cells to chromic ion. Alternatively, free chromate is washed away by centrifugation.

Waste management

Non-radioactive waste should be separated from radioactive waste to minimize storage requirements; and it should be disposed of as normal hospital waste. Shielded waste bins should be lined with plastic liners that can be easily removed when full. Technetium-99m is the main isotope in use in the radiopharmacy: the duration of storage will be determined by its half-life of 6.02 hours. Longer lived waste should be stored separately. Radioactive waste generated daily within the radiopharmacy includes syringes, elution vials, pharmaceutical vials, needles and swabs. Waste arising from the preparation and dispensing of radiopharmaceuticals should be primarily disposed in the waste bin built into the contained workstation/LAFC. Some bulky items such as paper waste and gloves may be disposed in a shielded waste bin in the pharmacy, as long as there is no risk of contaminating the room by removing them from the cabinet. Radioactive waste contaminated by blood (e.g. syringes following cell labelling procedures) should not be left in the workstation but removed to a shielded bin.

The waste container in the workstation should not be allowed to overflow and should be emptied regularly. The bin is best emptied before starting work in the cabinet, when the waste in the bin has decayed overnight. Segregation of waste according to half-life is good practice and can reduce the length of time that waste arising from shorter lived isotopes has to be stored.

All radioactive waste - sharps bins, paper waste, and ventilation kits - should be securely stored and monitored regularly. Waste should be checked by using a suitable meter in a low background environment and should be disposed of, once it has decayed to background level. Any items above background should be retained for a further period of decay in storage. All radioactive warning labels should be removed from waste, prior to disposal in hospital waste. The hospital waste disposal policy should be adhered to. (EANM, 2008)

Radiopharmacy facility


It is of importance to have a distinct separation between radiopharmaceutical preparation (aseptic processing) and blood cell labelling. This is to minimize the risk of cross-contamination in the facility. Restricted access is imperative from both a radiation security and pharmaceutical manufacturing point of view. The design of a radiopharmacy should take into account daily operational protocols, proper utilization of available space, and provisions for future growth. For radioprotection, the production area should be at negative pressure relative to the outside area (containment of gaseous or aerosol discharge), while pharmaceutical aseptic units are at positive pressure to minimize ingress of microbes. The compromise is a negative pressure isolator within a positive pressure room. From a pharmaceutical point of view, there should be a minimum number of trained staff, whereas for radioprotection there should be a rotation of staff to share the radiation dose.

The clean areas should be lined (floor, walls, and ceiling) with a smooth, continuous, impervious, non-absorbent, cleanable material such as welded sheet vinyl. Corners should be coved (curved) to minimize dirt collection. Light fixtures should be recessed and flush with the surface. Benches must be made of impervious material (solid is preferred over laminate) and may require additional support for lead shielding.

There should be transfer hatches with reliable interlocking doors so supplies can be sanitized and passed into the next room without allowing direct contact to maintain the integrity of products and processes.

Cleanroom Transfer Hatch

 Entry/change rooms should have interlocking doors and a physical barrier, or at least a line on the floor, to demarcate the two sides. Changing on entry will involve, at a minimum: clean low-lint lab coat, shoe covers, hair cover, and gloves.




LAF unit for "Tcm and 113Inm generators

LAF unit for blood cell labelling

Glove box or fume hood for handling 131I for therapy


Oven to dry and sterilize glassware

Autoclave (small but with program for liquids, if automated)

Lead bricks for shielding generators

Lead pots

Lead shielding for syringes

Lead-glass for use when inspecting products


Water bath (small - up to 100°C)

Semi-micro balance

Trays for handling radioactivity


Membrane filter

Laboratory glassware

Equipment for thin-layer chromatography

Equipment for sterility testing

Contamination monitor

Temperature recording device

Dose calibrator or similar ionization chamber type instrument

Well gamma counter

This equipment should be dedicated to use in the radiopharmacy and not shared with outside users.

Aseptic manipulations should be performed either in a pharmaceutical isolator or a laminar airflow hood.


There must be sufficient personnel at all levels who are qualified by professional training and experience to carry out the various jobs required. Staff qualifications should not only be sufficient but should be compatible with the type and amount of work.

Nuclear medicine centers have several ways of obtaining and preparing radiopharmaceuticals, ranging from the supply of unit doses by an outside provider, to preparing radiopharmaceuticals using commercial kits, to a full on-site service with manufacturing and blood cell labelling. Within a nuclear medicine center the person responsible for radiopharmaceuticals needs to develop systems for the:

• Procurement of radionuclides/radiopharmaceuticals;

• Storage and waste management of radionuclides/radiopharmaceuticals;

• Development of safe procedures and practices for the preparation and manipulation of radiopharmaceuticals, in consultation with relevant staff; and

• Implementation of a quality assurance program for radiopharmaceuticals.


In many institutions the procurement, storage, reconstitution of ‘cold kits’, dispensing of patient radiopharmaceutical doses, and cell labelling may be performed by a nuclear medicine technologist, or a medical physicist. More complex radiopharmaceutical preparation requires the expertise of a radiopharmacist/radiochemist.

All staff must wear a personal dosimeter (TLD, film badge, electronic dosimeter). In addition to their regular whole body dosimeter, staff preparing and handling radioactive materials should wear a finger thermoluminescent dosimeter (TLD) to monitor extremity dose. Prior to each use, the TLD should be wiped, using an alcohol wipe, and worn inside the glove. Upon leaving the preparation area, the finger TLD should be removed and appropriately stored.

Staff should ensure that they wash their hands thoroughly prior to working in the radiopharmacy. Before a person enters an area where radioactive substances are handled, any cut or break in the skin should be covered. Dressings should incorporate a waterproof adhesive strapping. Protective coats or gowns should be worn for preparation and dispensing of radiopharmaceuticals. Disposable gowns offer benefits in terms of maintaining sterility. Gloves worn in the laminar flow cabinet (LAFC) or contained workstation must be powder free in order to prevent clogging of the air filters within the cabinet. Alcohol rub should be rubbed onto gloves and allowed to evaporate before entering the LAFC. After handling radioactive materials, gloves must always be removed and disposed of as radioactive waste before handling/touching any other materials/surfaces within the radiopharmacy. Hands should be washed again after removal of gloves. Upon leaving the radiopharmacy, disposable gowns should be removed. Prior to disposal, they should be stored as radioactive waste until monitoring confirms that they are at background radiation levels.


The use of protective equipment, when handling radioactive materials, can have a significant impact on reducing staff dose. Laboratories and other work areas for manipulation of unsealed radioactive substances should be provided with equipment kept specifically for this purpose, and should include the following:

  1. Tools for maximizing the distance from the source, e.g. tongs and forceps
  2. Syringe shields
  3. Vial shields
  4. Drip trays for minimizing the spread of contamination in the case of spillage
  5. Shielded syringe carriers
  6. Decontamination kit

Unshielded syringes or vials should never be used during manipulation of radiopharmaceuticals. Equipment should be stored outside the laminar flow cabinet when not in use and should be cleaned regularly in accordance with local recommendations.

Principles of Radiation Protection

International Commission on Radiological Protection (ICRP) proposed a system of radiation protection. The general principles of radiation protection are:

  • Justification: All procedures involving radioactive material must be justified.
  • Optimization: The radiation exposure to any individual should be as low as reasonably achievable. This principle is the widely known ALARA concept (As Low As Reasonably Achievable).
  • Limitation: The radiation dose received by the personnel handling radioactive material will never exceed the legally established dose limits.

ICRP revised its recommendations and extended its philosophy to a system of radiological protection while keeping the fundamental principles of protection.

When planning facilities and procedures for handling of radioactive materials according to the ALARA principle, it is important to keep in mind the basic principles for reduction of radiation doses:

  • Time: The shorter the time of exposure to radiation, the lower the dose to the operator.
  • Distance: The radiation dose decreases with a factor equal to the square root of the distance from the radiation source. The operator’s distance from the source can be increased by using forceps, tongs, or manipulators in handling the radioactive material.
  • Shielding: The radiation dose can be reduced by placing shielding material between the source and the operator. For protection against gamma radiation, walls made of heavy concrete or lead bricks are used. For transport containers, material such as tungsten may be used for higher energy gamma irradiation radionuclides, giving a higher shielding per weight unit when compared to lead.

Categories of Exposure

  1. Occupational exposure

Occupational exposure is defined as all radiation exposure of workers incurred as a result of their work. ICRP limits its use of ‘occupational exposures’ to radiation exposures incurred at work as a result of situations that can reasonably be regarded as being the responsibility of the operating management. The employer has the main responsibility for the protection of workers.

  1. Public exposure

Public exposure encompasses all exposures of the public other than occupational exposures and medical exposures of patients. It is incurred as a result of a range of radiation sources. The component of public exposure due to natural sources is by far the largest, but this provides no justification for reducing the attention paid to smaller, but more readily controllable, exposures to man-made sources. Exposures of the embryo and fetus of pregnant workers are considered and regulated as public exposures.

  1. Medical exposure of patients

Radiation exposures of patients occur in diagnostic, interventional, and therapeutic procedures. There are several features of radiological practices in medicine that require an approach that differs from the radiological protection in other planned exposure situations. The exposure is intentional and for the direct benefit of the patient. The application of these Recommendations to the medical uses of radiation therefore requires separate guidance.



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  6. European Association of Nuclear Medicine (EANM) Technologists Committee, 2008. The Radiopharmacy: A Technologist’s Guide.
  7. International Atomic Energy Agency, 1979. Technical Report Series No. 194: Preparation and Control of Radiopharmaceuticals in Hospitals. Vienna, Austria.